WIP: completedyndep

26 files changed, 2537 insertions, 1197 deletions

diff --git a/libbuild2/adhoc-rule-buildscript.cxx b/libbuild2/adhoc-rule-buildscript.cxx
index aa320e2..78f87ae 100644
--- a/libbuild2/adhoc-rule-buildscript.cxx
+++ b/libbuild2/adhoc-rule-buildscript.cxx
@@ -8,8 +8,8 @@
 #include <libbuild2/depdb.hxx>
 #include <libbuild2/scope.hxx>
 #include <libbuild2/target.hxx>
+#include <libbuild2/dyndep.hxx>
 #include <libbuild2/context.hxx>
-#include <libbuild2/dynamic.hxx>
 #include <libbuild2/algorithm.hxx>
 #include <libbuild2/filesystem.hxx>  // path_perms(), auto_rmfile
 #include <libbuild2/diagnostics.hxx>
@@ -226,9 +226,10 @@ namespace build2
     build::script::environment env;
     build::script::default_runner run;
 
+    path dd;
     const scope* bs;
     timestamp mt;
-    path dd;
+    bool deferred_failure;
   };
 
   bool adhoc_buildscript_rule::
@@ -329,16 +330,16 @@ namespace build2
 
     // See if this is the simple case with only static dependencies.
     //
-    if (!script.depdb_pre_dynamic)
+    if (!script.depdb_dyndep)
     {
       return [this] (action a, const target& t)
       {
-        return perform_update_file_static (a, t);
+        return perform_update_file (a, t);
       };
     }
 
     // This is a perform update on a file target with extraction of dynamic
-    // dependency information in the depdb preamble (depdb-pre-dynamic).
+    // dependency information in the depdb preamble (depdb-dyndep).
     //
     // This means we may need to add additional prerequisites (or even target
     // group members). We also have to save any such additional prerequisites
@@ -355,7 +356,7 @@ namespace build2
     //
     context& ctx (xt.ctx);
 
-    const file& t (xt.as<file> ());
+    file& t (xt.as<file> ());
     const path& tp (t.path ());
 
     if (dir != nullptr)
@@ -369,12 +370,12 @@ namespace build2
     auto& pts (t.prerequisite_targets[a]);
     for (prerequisite_target& p: pts)
     {
+      // Note that fsdir{} injected above is adhoc.
+      //
       if (p.target != nullptr && p.adhoc)
       {
-        // Blank out injected fsdir{} for good.
-        //
-        if (p.target != dir)
-          p.data = reinterpret_cast<uintptr_t> (p.target);
+        p.data = reinterpret_cast<uintptr_t> (p.target);
+        p.target = nullptr;
       }
     }
 
@@ -444,11 +445,11 @@ namespace build2
 
     run.enter (env, script.start_loc);
 
-    // Run the first half of the preamble (before depdb-pre-dynamic).
+    // Run the first half of the preamble (before depdb-dyndep).
     //
     {
       build::script::parser p (ctx);
-      p.execute_depdb_preamble (bs, env, script, run, dd);
+      p.execute_depdb_preamble (a, bs, t, env, script, run, dd);
     }
 
     // Determine if we need to do an update based on the above checks.
@@ -470,7 +471,7 @@ namespace build2
       mt = timestamp_nonexistent;
 
     // Update our prerequisite targets. While strictly speaking we only need
-    // to update those that are referenced by depdb-pre-dynamic, communicating
+    // to update those that are referenced by depdb-dyndep, communicating
     // this is both tedious and error-prone. So we update them all.
     //
     for (const prerequisite_target& p: pts)
@@ -484,14 +485,21 @@ namespace build2
       }
     }
 
-    // Run the second half of the preamble (depdb-pre-dynamic commands) to
-    // extract dynamic dependencies.
+    // Run the second half of the preamble (depdb-dyndep commands) to extract
+    // dynamic dependencies.
     //
     // Note that this should be the last update to depdb (the invalidation
     // order semantics).
+    //
+    bool deferred_failure (false);
     {
       build::script::parser p (ctx);
-      p.execute_depdb_preamble_dynamic (bs, env, script, run, dd, update, mt);
+      p.execute_depdb_preamble_dyndep (a, bs, t,
+                                       env, script, run,
+                                       dd,
+                                       update,
+                                       deferred_failure,
+                                       mt);
     }
 
     if (update && dd.reading () && !ctx.dry_run)
@@ -504,13 +512,14 @@ namespace build2
     //
     md->bs = &bs;
     md->mt = update ? timestamp_nonexistent : mt;
+    md->deferred_failure = deferred_failure;
 
     // @@ TMP: re-enable once recipe becomes move_only_function.
     //
 #if 0
     return [this, md = move (md)] (action a, const target& t) mutable
     {
-      auto r (perform_update_file_dynamic (a, t, *md));
+      auto r (perform_update_file_dyndep (a, t, *md));
       md.reset (); // @@ TMP: is this really necessary (+mutable)?
       return r;
     };
@@ -519,16 +528,15 @@ namespace build2
     return recipe ([this] (action a, const target& t) mutable
     {
       auto md (move (t.data<unique_ptr<match_data>> ()));
-      return perform_update_file_dynamic (a, t, *md);
+      return perform_update_file_dyndep (a, t, *md);
     });
 #endif
   }
 
   target_state adhoc_buildscript_rule::
-  perform_update_file_dynamic (action a, const target& xt,
-                               match_data& md) const
+  perform_update_file_dyndep (action a, const target& xt, match_data& md) const
   {
-    tracer trace ("adhoc_buildscript_rule::perform_update_file_dynamic");
+    tracer trace ("adhoc_buildscript_rule::perform_update_file_dyndep");
 
     context& ctx (xt.ctx);
 
@@ -544,7 +552,7 @@ namespace build2
           (p.target != nullptr ? p.target :
            p.data   != 0       ? reinterpret_cast<target*> (p.data) : nullptr))
       {
-        target_state ts (execute (a, *pt));
+        target_state ts (execute_wait (a, *pt));
         assert (ts == target_state::unchanged || ts == target_state::changed);
       }
     }
@@ -552,7 +560,9 @@ namespace build2
     build::script::environment& env (md.env);
     build::script::default_runner& run (md.run);
 
-    if (md.mt != timestamp_nonexistent)
+    // Force update in case of a deferred failure even if nothing changed.
+    //
+    if (md.mt != timestamp_nonexistent && !md.deferred_failure)
     {
       run.leave (env, script.end_loc);
       return target_state::unchanged;
@@ -566,7 +576,7 @@ namespace build2
 
     if (!ctx.dry_run || verb != 0)
     {
-      if (execute_update_file (*md.bs, a, t, env, run))
+      if (execute_update_file (*md.bs, a, t, env, run, md.deferred_failure))
         ;
       else
         run.leave (env, script.end_loc);
@@ -584,9 +594,9 @@ namespace build2
   }
 
   target_state adhoc_buildscript_rule::
-  perform_update_file_static (action a, const target& xt) const
+  perform_update_file (action a, const target& xt) const
   {
-    tracer trace ("adhoc_buildscript_rule::perform_update_file_static");
+    tracer trace ("adhoc_buildscript_rule::perform_update_file");
 
     context& ctx (xt.ctx);
 
@@ -671,8 +681,6 @@ namespace build2
         // As part of this loop calculate checksums that need to include ad
         // hoc prerequisites (unless the script tracks changes itself).
         //
-        // @@ TODO: skip fsdir{}?
-        //
         if (!script.depdb_clear)
           hash_prerequisite_target (prq_cs, exe_cs, env_cs, pt, storage);
       }
@@ -805,7 +813,7 @@ namespace build2
       build::script::parser p (ctx);
 
       run.enter (env, script.start_loc);
-      p.execute_depdb_preamble (*bs, env, script, run, dd);
+      p.execute_depdb_preamble (a, *bs, t, env, script, run, dd);
     }
 
     // Update if depdb mismatch.
@@ -855,10 +863,13 @@ namespace build2
   execute_update_file (const scope& bs,
                        action, const file& t,
                        build::script::environment& env,
-                       build::script::default_runner& run) const
+                       build::script::default_runner& run,
+                       bool deferred_failure) const
   {
     context& ctx (t.ctx);
 
+    const scope& rs (*bs.root_scope ());
+
     // Note that it doesn't make much sense to use the temporary directory
     // variable ($~) in the 'diag' builtin call, so we postpone setting it
     // until the script body execution, that can potentially be omitted.
@@ -869,7 +880,7 @@ namespace build2
     {
       if (script.diag_line)
       {
-        text << p.execute_special (bs, env, *script.diag_line);
+        text << p.execute_special (rs, bs, env, *script.diag_line);
       }
       else
       {
@@ -905,10 +916,13 @@ namespace build2
       if (script.body_temp_dir && !script.depdb_preamble_temp_dir)
         env.set_temp_dir_variable ();
 
-      p.execute_body (bs, env, script, run, script.depdb_preamble.empty ());
+      p.execute_body (rs, bs, env, script, run, script.depdb_preamble.empty ());
 
       if (!ctx.dry_run)
       {
+        if (deferred_failure)
+          fail << "expected error exit status from recipe body";
+
         // If this is an executable, let's be helpful to the user and set
         // the executable bit on POSIX.
         //
@@ -952,6 +966,7 @@ namespace build2
     if (!ctx.dry_run || verb != 0)
     {
       const scope& bs (t.base_scope ());
+      const scope& rs (*bs.root_scope ());
 
       build::script::environment e (a, t, script.body_temp_dir, deadline);
       build::script::parser p (ctx);
@@ -960,7 +975,7 @@ namespace build2
       {
         if (script.diag_line)
         {
-          text << p.execute_special (bs, e, *script.diag_line);
+          text << p.execute_special (rs, bs, e, *script.diag_line);
         }
         else
         {
@@ -973,7 +988,7 @@ namespace build2
       if (!ctx.dry_run || verb >= 2)
       {
         build::script::default_runner r;
-        p.execute_body (bs, e, script, r);
+        p.execute_body (rs, bs, e, script, r);
       }
     }
 
diff --git a/libbuild2/adhoc-rule-buildscript.hxx b/libbuild2/adhoc-rule-buildscript.hxx
index 7ec647b..51d37d4 100644
--- a/libbuild2/adhoc-rule-buildscript.hxx
+++ b/libbuild2/adhoc-rule-buildscript.hxx
@@ -36,18 +36,19 @@ namespace build2
            const optional<timestamp>&) const override;
 
     target_state
-    perform_update_file_static (action, const target&) const;
+    perform_update_file (action, const target&) const;
 
     struct match_data;
 
     target_state
-    perform_update_file_dynamic (action, const target&, match_data&) const;
+    perform_update_file_dyndep (action, const target&, match_data&) const;
 
     bool
     execute_update_file (const scope&,
                          action a, const file&,
                          build::script::environment&,
-                         build::script::default_runner&) const;
+                         build::script::default_runner&,
+                         bool deferred_failure = false) const;
 
     target_state
     default_action (action, const target&, const optional<timestamp>&) const;
diff --git a/libbuild2/build/script/builtin-options.cxx b/libbuild2/build/script/builtin-options.cxx
index dfb8e62..cf99b12 100644
--- a/libbuild2/build/script/builtin-options.cxx
+++ b/libbuild2/build/script/builtin-options.cxx
@@ -6,6 +6,7 @@
 
 // Begin prologue.
 //
+#include <libbuild2/build/script/types-parsers.hxx>
 //
 // End prologue.
 
@@ -404,86 +405,77 @@ namespace build2
       : file_ (),
         file_specified_ (false),
         format_ (),
-        format_specified_ (false)
+        format_specified_ (false),
+        what_ (),
+        what_specified_ (false),
+        include_path_ (),
+        include_path_specified_ (false),
+        default_prereq_type_ (),
+        default_prereq_type_specified_ (false)
       {
       }
 
-      depdb_dep_options::
-      depdb_dep_options (int& argc,
-                         char** argv,
-                         bool erase,
-                         ::build2::build::script::cli::unknown_mode opt,
-                         ::build2::build::script::cli::unknown_mode arg)
-      : file_ (),
-        file_specified_ (false),
-        format_ (),
-        format_specified_ (false)
+      bool depdb_dep_options::
+      parse (int& argc,
+             char** argv,
+             bool erase,
+             ::build2::build::script::cli::unknown_mode opt,
+             ::build2::build::script::cli::unknown_mode arg)
       {
         ::build2::build::script::cli::argv_scanner s (argc, argv, erase);
-        _parse (s, opt, arg);
+        bool r = _parse (s, opt, arg);
+        return r;
       }
 
-      depdb_dep_options::
-      depdb_dep_options (int start,
-                         int& argc,
-                         char** argv,
-                         bool erase,
-                         ::build2::build::script::cli::unknown_mode opt,
-                         ::build2::build::script::cli::unknown_mode arg)
-      : file_ (),
-        file_specified_ (false),
-        format_ (),
-        format_specified_ (false)
+      bool depdb_dep_options::
+      parse (int start,
+             int& argc,
+             char** argv,
+             bool erase,
+             ::build2::build::script::cli::unknown_mode opt,
+             ::build2::build::script::cli::unknown_mode arg)
       {
         ::build2::build::script::cli::argv_scanner s (start, argc, argv, erase);
-        _parse (s, opt, arg);
+        bool r = _parse (s, opt, arg);
+        return r;
       }
 
-      depdb_dep_options::
-      depdb_dep_options (int& argc,
-                         char** argv,
-                         int& end,
-                         bool erase,
-                         ::build2::build::script::cli::unknown_mode opt,
-                         ::build2::build::script::cli::unknown_mode arg)
-      : file_ (),
-        file_specified_ (false),
-        format_ (),
-        format_specified_ (false)
+      bool depdb_dep_options::
+      parse (int& argc,
+             char** argv,
+             int& end,
+             bool erase,
+             ::build2::build::script::cli::unknown_mode opt,
+             ::build2::build::script::cli::unknown_mode arg)
       {
         ::build2::build::script::cli::argv_scanner s (argc, argv, erase);
-        _parse (s, opt, arg);
+        bool r = _parse (s, opt, arg);
         end = s.end ();
+        return r;
       }
 
-      depdb_dep_options::
-      depdb_dep_options (int start,
-                         int& argc,
-                         char** argv,
-                         int& end,
-                         bool erase,
-                         ::build2::build::script::cli::unknown_mode opt,
-                         ::build2::build::script::cli::unknown_mode arg)
-      : file_ (),
-        file_specified_ (false),
-        format_ (),
-        format_specified_ (false)
+      bool depdb_dep_options::
+      parse (int start,
+             int& argc,
+             char** argv,
+             int& end,
+             bool erase,
+             ::build2::build::script::cli::unknown_mode opt,
+             ::build2::build::script::cli::unknown_mode arg)
       {
         ::build2::build::script::cli::argv_scanner s (start, argc, argv, erase);
-        _parse (s, opt, arg);
+        bool r = _parse (s, opt, arg);
         end = s.end ();
+        return r;
       }
 
-      depdb_dep_options::
-      depdb_dep_options (::build2::build::script::cli::scanner& s,
-                         ::build2::build::script::cli::unknown_mode opt,
-                         ::build2::build::script::cli::unknown_mode arg)
-      : file_ (),
-        file_specified_ (false),
-        format_ (),
-        format_specified_ (false)
+      bool depdb_dep_options::
+      parse (::build2::build::script::cli::scanner& s,
+             ::build2::build::script::cli::unknown_mode opt,
+             ::build2::build::script::cli::unknown_mode arg)
       {
-        _parse (s, opt, arg);
+        bool r = _parse (s, opt, arg);
+        return r;
       }
 
       typedef
@@ -497,11 +489,23 @@ namespace build2
         _cli_depdb_dep_options_map_init ()
         {
           _cli_depdb_dep_options_map_["--file"] =
-          &::build2::build::script::cli::thunk< depdb_dep_options, string, &depdb_dep_options::file_,
+          &::build2::build::script::cli::thunk< depdb_dep_options, path, &depdb_dep_options::file_,
             &depdb_dep_options::file_specified_ >;
           _cli_depdb_dep_options_map_["--format"] =
           &::build2::build::script::cli::thunk< depdb_dep_options, string, &depdb_dep_options::format_,
             &depdb_dep_options::format_specified_ >;
+          _cli_depdb_dep_options_map_["--what"] =
+          &::build2::build::script::cli::thunk< depdb_dep_options, string, &depdb_dep_options::what_,
+            &depdb_dep_options::what_specified_ >;
+          _cli_depdb_dep_options_map_["--include-path"] =
+          &::build2::build::script::cli::thunk< depdb_dep_options, dir_paths, &depdb_dep_options::include_path_,
+            &depdb_dep_options::include_path_specified_ >;
+          _cli_depdb_dep_options_map_["-I"] =
+          &::build2::build::script::cli::thunk< depdb_dep_options, dir_paths, &depdb_dep_options::include_path_,
+            &depdb_dep_options::include_path_specified_ >;
+          _cli_depdb_dep_options_map_["--default-prereq-type"] =
+          &::build2::build::script::cli::thunk< depdb_dep_options, string, &depdb_dep_options::default_prereq_type_,
+            &depdb_dep_options::default_prereq_type_specified_ >;
         }
       };
 
diff --git a/libbuild2/build/script/builtin-options.hxx b/libbuild2/build/script/builtin-options.hxx
index ccfd54b..85d67b9 100644
--- a/libbuild2/build/script/builtin-options.hxx
+++ b/libbuild2/build/script/builtin-options.hxx
@@ -302,48 +302,55 @@ namespace build2
         public:
         depdb_dep_options ();
 
-        depdb_dep_options (int& argc,
-                           char** argv,
-                           bool erase = false,
-                           ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
-                           ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
-
-        depdb_dep_options (int start,
-                           int& argc,
-                           char** argv,
-                           bool erase = false,
-                           ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
-                           ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
-
-        depdb_dep_options (int& argc,
-                           char** argv,
-                           int& end,
-                           bool erase = false,
-                           ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
-                           ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
-
-        depdb_dep_options (int start,
-                           int& argc,
-                           char** argv,
-                           int& end,
-                           bool erase = false,
-                           ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
-                           ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
-
-        depdb_dep_options (::build2::build::script::cli::scanner&,
-                           ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
-                           ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
+        // Return true if anything has been parsed.
+        //
+        bool
+        parse (int& argc,
+               char** argv,
+               bool erase = false,
+               ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
+               ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
+
+        bool
+        parse (int start,
+               int& argc,
+               char** argv,
+               bool erase = false,
+               ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
+               ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
+
+        bool
+        parse (int& argc,
+               char** argv,
+               int& end,
+               bool erase = false,
+               ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
+               ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
+
+        bool
+        parse (int start,
+               int& argc,
+               char** argv,
+               int& end,
+               bool erase = false,
+               ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
+               ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
+
+        bool
+        parse (::build2::build::script::cli::scanner&,
+               ::build2::build::script::cli::unknown_mode option = ::build2::build::script::cli::unknown_mode::fail,
+               ::build2::build::script::cli::unknown_mode argument = ::build2::build::script::cli::unknown_mode::stop);
 
         // Option accessors and modifiers.
         //
-        const string&
+        const path&
         file () const;
 
-        string&
+        path&
         file ();
 
         void
-        file (const string&);
+        file (const path&);
 
         bool
         file_specified () const;
@@ -366,6 +373,51 @@ namespace build2
         void
         format_specified (bool);
 
+        const string&
+        what () const;
+
+        string&
+        what ();
+
+        void
+        what (const string&);
+
+        bool
+        what_specified () const;
+
+        void
+        what_specified (bool);
+
+        const dir_paths&
+        include_path () const;
+
+        dir_paths&
+        include_path ();
+
+        void
+        include_path (const dir_paths&);
+
+        bool
+        include_path_specified () const;
+
+        void
+        include_path_specified (bool);
+
+        const string&
+        default_prereq_type () const;
+
+        string&
+        default_prereq_type ();
+
+        void
+        default_prereq_type (const string&);
+
+        bool
+        default_prereq_type_specified () const;
+
+        void
+        default_prereq_type_specified (bool);
+
         // Implementation details.
         //
         protected:
@@ -379,10 +431,16 @@ namespace build2
                 ::build2::build::script::cli::unknown_mode argument);
 
         public:
-        string file_;
+        path file_;
         bool file_specified_;
         string format_;
         bool format_specified_;
+        string what_;
+        bool what_specified_;
+        dir_paths include_path_;
+        bool include_path_specified_;
+        string default_prereq_type_;
+        bool default_prereq_type_specified_;
       };
     }
   }
diff --git a/libbuild2/build/script/builtin-options.ixx b/libbuild2/build/script/builtin-options.ixx
index 3263803..06575c8 100644
--- a/libbuild2/build/script/builtin-options.ixx
+++ b/libbuild2/build/script/builtin-options.ixx
@@ -179,20 +179,20 @@ namespace build2
       // depdb_dep_options
       //
 
-      inline const string& depdb_dep_options::
+      inline const path& depdb_dep_options::
       file () const
       {
         return this->file_;
       }
 
-      inline string& depdb_dep_options::
+      inline path& depdb_dep_options::
       file ()
       {
         return this->file_;
       }
 
       inline void depdb_dep_options::
-      file (const string& x)
+      file (const path& x)
       {
         this->file_ = x;
       }
@@ -238,6 +238,96 @@ namespace build2
       {
         this->format_specified_ = x;
       }
+
+      inline const string& depdb_dep_options::
+      what () const
+      {
+        return this->what_;
+      }
+
+      inline string& depdb_dep_options::
+      what ()
+      {
+        return this->what_;
+      }
+
+      inline void depdb_dep_options::
+      what (const string& x)
+      {
+        this->what_ = x;
+      }
+
+      inline bool depdb_dep_options::
+      what_specified () const
+      {
+        return this->what_specified_;
+      }
+
+      inline void depdb_dep_options::
+      what_specified (bool x)
+      {
+        this->what_specified_ = x;
+      }
+
+      inline const dir_paths& depdb_dep_options::
+      include_path () const
+      {
+        return this->include_path_;
+      }
+
+      inline dir_paths& depdb_dep_options::
+      include_path ()
+      {
+        return this->include_path_;
+      }
+
+      inline void depdb_dep_options::
+      include_path (const dir_paths& x)
+      {
+        this->include_path_ = x;
+      }
+
+      inline bool depdb_dep_options::
+      include_path_specified () const
+      {
+        return this->include_path_specified_;
+      }
+
+      inline void depdb_dep_options::
+      include_path_specified (bool x)
+      {
+        this->include_path_specified_ = x;
+      }
+
+      inline const string& depdb_dep_options::
+      default_prereq_type () const
+      {
+        return this->default_prereq_type_;
+      }
+
+      inline string& depdb_dep_options::
+      default_prereq_type ()
+      {
+        return this->default_prereq_type_;
+      }
+
+      inline void depdb_dep_options::
+      default_prereq_type (const string& x)
+      {
+        this->default_prereq_type_ = x;
+      }
+
+      inline bool depdb_dep_options::
+      default_prereq_type_specified () const
+      {
+        return this->default_prereq_type_specified_;
+      }
+
+      inline void depdb_dep_options::
+      default_prereq_type_specified (bool x)
+      {
+        this->default_prereq_type_specified_ = x;
+      }
     }
   }
 }
diff --git a/libbuild2/build/script/builtin.cli b/libbuild2/build/script/builtin.cli
index 6e66d67..3ed3659 100644
--- a/libbuild2/build/script/builtin.cli
+++ b/libbuild2/build/script/builtin.cli
@@ -17,8 +17,15 @@ namespace build2
       //
       class depdb_dep_options
       {
-        string --file; // @@ TMP path
-        string --format;
+        // Note that --byproduct, if any, must be the first option and is
+        // handled ad hoc, kind of as a sub-command.
+        //
+        path --file;                   // Read from file rather than stdin.
+        string --format;               // Dependency format: make (default).
+        string --what;                 // Dependency kind, e.g., "header".
+        dir_paths --include-path|-I;   // Search paths for generated files.
+        string --default-prereq-type;  // Default prerequisite type to use
+                                       // if none could be derived from ext.
       };
     }
   }
diff --git a/libbuild2/build/script/parser.cxx b/libbuild2/build/script/parser.cxx
index c6d7d49..67dbf69 100644
--- a/libbuild2/build/script/parser.cxx
+++ b/libbuild2/build/script/parser.cxx
@@ -3,11 +3,16 @@
 
 #include <libbuild2/build/script/parser.hxx>
 
+#include <cstring> // strcmp()
+#include <sstream>
+
 #include <libbutl/builtin.hxx>
 
 #include <libbuild2/depdb.hxx>
+#include <libbuild2/dyndep.hxx>
 #include <libbuild2/function.hxx>
 #include <libbuild2/algorithm.hxx>
+#include <libbuild2/make-parser.hxx>
 
 #include <libbuild2/script/run.hxx>
 
@@ -129,8 +134,8 @@ namespace build2
         // Save the custom dependency change tracking lines, if present.
         //
         s.depdb_clear = depdb_clear_.has_value ();
-        if (depdb_pre_dynamic_)
-          s.depdb_pre_dynamic = depdb_pre_dynamic_->second;
+        if (depdb_dyndep_)
+          s.depdb_dyndep = depdb_dyndep_->second;
         s.depdb_preamble = move (depdb_preamble_);
 
         return s;
@@ -497,7 +502,7 @@ namespace build2
                  v != "hash"   &&
                  v != "string" &&
                  v != "env"    &&
-                 v != "pre-dynamic"))
+                 v != "dyndep"))
             {
               fail (get_location (t))
                 << "expected 'depdb' builtin command instead of " << t;
@@ -543,28 +548,31 @@ namespace build2
             }
             else
             {
-              // Verify depdb-pre-dynamic is last.
+              // Verify depdb-dyndep is last.
               //
-              if (v == "pre-dynamic")
+              if (v == "dyndep")
               {
-                // Note that for now we do not allow multiple pre-dynamic
-                // calls. But we may wan to relax this later (though
-                // alternating targets with prerequisites may be tricky --
-                // maybe still only allow additional targets in the first
-                // call).
+                // Note that for now we do not allow multiple dyndep calls.
+                // But we may wan to relax this later (though alternating
+                // targets with prerequisites in depdb may be tricky -- maybe
+                // still only allow additional targets in the first call).
                 //
-                if (!depdb_pre_dynamic_)
-                  depdb_pre_dynamic_ = make_pair (l, depdb_preamble_.size ());
+                if (!depdb_dyndep_)
+                  depdb_dyndep_ = make_pair (l, depdb_preamble_.size ());
                 else
-                  fail (l) << "multiple 'depdb pre-dynamic' calls" <<
-                    info (depdb_pre_dynamic_->first) << "previous call is here";
+                  fail (l) << "multiple 'depdb dyndep' calls" <<
+                    info (depdb_dyndep_->first) << "previous call is here";
+
+#if 0
+                if (peek () == type::word && peeked ().value == "--byproduct")
+                  ;
+#endif
               }
               else
               {
-                if (depdb_pre_dynamic_)
-                  fail (l) << "'depdb " << v << "' after 'depdb pre-dynamic'" <<
-                    info (depdb_pre_dynamic_->first)
-                           << "'depdb pre-dynamic' call is here";
+                if (depdb_dyndep_)
+                  fail (l) << "'depdb " << v << "' after 'depdb dyndep'" <<
+                    info (depdb_dyndep_->first) << "'depdb dyndep' call is here";
               }
 
               // Move the script body to the end of the depdb preamble.
@@ -885,11 +893,11 @@ namespace build2
       }
 
       void parser::
-      execute_body (const scope& bs,
+      execute_body (const scope& rs, const scope& bs,
                     environment& e, const script& s, runner& r,
                     bool enter, bool leave)
       {
-        pre_exec (*bs.root_scope (), bs, e, &s, &r);
+        pre_exec (rs, bs, e, &s, &r);
 
         if (enter)
           runner_->enter (e, s.start_loc);
@@ -919,10 +927,13 @@ namespace build2
       }
 
       void parser::
-      exec_depdb_preamble (const scope& bs,
+      exec_depdb_preamble (action a, const scope& bs, const file& t,
                            environment& e, const script& s, runner& r,
                            lines_iterator begin, lines_iterator end,
-                           depdb& dd, bool* update, optional<timestamp> mt)
+                           depdb& dd,
+                           bool* update,
+                           bool* deferred_failure,
+                           optional<timestamp> mt)
       {
         tracer trace ("exec_depdb_preamble");
 
@@ -938,12 +949,20 @@ namespace build2
         struct
         {
           tracer& trace;
+
+          action a;
+          const scope& bs;
+          const file& t;
+
           environment& env;
           const script& scr;
+
           depdb& dd;
           bool* update;
+          bool* deferred_failure;
           optional<timestamp> mt;
-        } data {trace, e, s, dd, update, mt};
+
+        } data {trace, a, bs, t, e, s, dd, update, deferred_failure, mt};
 
         auto exec_cmd = [this, &data] (token& t,
                                        build2::script::token_type& tt,
@@ -965,14 +984,17 @@ namespace build2
 
             string cmd (move (t.value));
 
-            if (cmd == "pre-dynamic")
+            if (cmd == "dyndep")
             {
-              exec_depdb_pre_dynamic (t, tt,
-                                      li, ll,
-                                      data.env.target,
-                                      data.dd,
-                                      *data.update,
-                                      *data.mt);
+              // Note: cast is safe since this is always executed in apply().
+              //
+              exec_depdb_dyndep (t, tt,
+                                 li, ll,
+                                 data.a, data.bs, const_cast<file&> (data.t),
+                                 data.dd,
+                                 *data.update,
+                                 *data.deferred_failure,
+                                 *data.mt);
             }
             else
             {
@@ -988,7 +1010,7 @@ namespace build2
                   l4 ([&] {
                       data.trace (ll)
                         << "'depdb hash' argument change forcing update of "
-                        << data.env.target;});
+                        << data.t;});
               }
               else if (cmd == "string")
               {
@@ -1006,7 +1028,7 @@ namespace build2
                   l4 ([&] {
                       data.trace (ll)
                         << "'depdb string' argument change forcing update of "
-                        << data.env.target;});
+                        << data.t;});
               }
               else if (cmd == "env")
               {
@@ -1031,7 +1053,7 @@ namespace build2
                   l4 ([&] {
                       data.trace (ll)
                         << "'depdb env' environment change forcing update of "
-                        << data.env.target;});
+                        << data.t;});
               }
               else
                 assert (false);
@@ -1157,15 +1179,12 @@ namespace build2
       }
 
       names parser::
-      execute_special (const scope& bs,
+      execute_special (const scope& rs, const scope& bs,
                        environment& e,
                        const line& ln,
                        bool omit_builtin)
       {
-        pre_exec (*bs.root_scope (), bs,
-                  e,
-                  nullptr /* script */,
-                  nullptr /* runner */);
+        pre_exec (rs, bs, e, nullptr /* script */, nullptr /* runner */);
 
         // Copy the tokens and start playing.
         //
@@ -1182,113 +1201,415 @@ namespace build2
       }
 
       void parser::
-      exec_depdb_pre_dynamic (token& t, build2::script::token_type& tt,
-                              size_t li, const location& ll,
-                              const target& tgt,
-                              depdb& dd,
-                              bool& update,
-                              timestamp /*mt*/)
+      exec_depdb_dyndep (token& lt, build2::script::token_type& ltt,
+                         size_t li, const location& ll,
+                         action a, const scope& bs, file& t,
+                         depdb& dd,
+                         bool& update,
+                         bool& deferred_failure,
+                         timestamp mt)
       {
+        tracer trace ("exec_depdb_dyndep");
+
+        context& ctx (t.ctx);
+
         // Similar approach to parse_env_builtin().
         //
-        next (t, tt); // Skip 'dep' command.
-
-        // Note that an option name and value can belong to different name
-        // chunks. That's why we parse the arguments in the chunking mode into
-        // the list up to the `--` separator and parse this list into options
-        // afterwards. Note that the `--` separator should be omitted if there
-        // is no program (i.e., additional dependency info is being read from
-        // one of the prerequisites).
-        //
-        strings args;
+        depdb_dep_options ops;
         bool prog (false);
-
-        names ns; // Reuse to reduce allocations.
-        while (tt != type::newline && tt != type::eos)
         {
-          if (tt == type::word && t.value == "--")
-          {
-            prog = true;
-            break;
-          }
-
-          location l (get_location (t));
+          auto& t (lt);
+          auto& tt (ltt);
 
-          if (!start_names (tt))
-            fail (l) << "depdb pre-dynamic: expected option or '--' separator "
-                     << "instead of " << t;
+          next (t, tt); // Skip 'dep' command.
 
-          parse_names (t, tt,
-                       ns,
-                       pattern_mode::ignore,
-                       true /* chunk */,
-                       "depdb pre-dynamic builtin argument",
-                       nullptr);
+          // Note that an option name and value can belong to different name
+          // chunks. That's why we parse the arguments in the chunking mode
+          // into the list up to the `--` separator and parse this list into
+          // options afterwards. Note that the `--` separator should be
+          // omitted if there is no program (i.e., additional dependency info
+          // is being read from one of the prerequisites).
+          //
+          strings args;
 
-          for (name& n: ns)
+          names ns; // Reuse to reduce allocations.
+          while (tt != type::newline && tt != type::eos)
           {
-            try
+            if (tt == type::word && t.value == "--")
             {
-              args.push_back (convert<string> (move (n)));
+              prog = true;
+              break;
             }
-            catch (const invalid_argument&)
+
+            location l (get_location (t));
+
+            if (!start_names (tt))
+              fail (l) << "depdb dyndep: expected option or '--' separator "
+                       << "instead of " << t;
+
+            parse_names (t, tt,
+                         ns,
+                         pattern_mode::ignore,
+                         true /* chunk */,
+                         "depdb dyndep builtin argument",
+                         nullptr);
+
+            for (name& n: ns)
             {
-              diag_record dr (fail (l));
-              dr << "invalid string value ";
-              to_stream (dr.os, n, true /* quote */);
+              try
+              {
+                args.push_back (convert<string> (move (n)));
+              }
+              catch (const invalid_argument&)
+              {
+                diag_record dr (fail (l));
+                dr << "invalid string value ";
+                to_stream (dr.os, n, true /* quote */);
+              }
             }
+
+            ns.clear ();
           }
 
-          ns.clear ();
-        }
+          if (prog)
+          {
+            next (t, tt); // Skip '--'.
 
-        if (prog)
-        {
-          next (t, tt); // Skip '--'.
+            if (tt == type::newline || tt == type::eos)
+              fail (t) << "depdb dyndep: expected program name instead of "
+                       << t;
+          }
 
-          if (tt == type::newline || tt == type::eos)
-            fail (t) << "depdb pre-dynamic: expected program name instead of "
-                     << t;
+          // Parse the options.
+          //
+          // We would like to support both -I <dir> as well as -I<dir> forms
+          // for better compatibility. The latter requires manual parsing.
+          //
+          try
+          {
+            for (cli::vector_scanner scan (args); scan.more (); )
+            {
+              if (ops.parse (scan, cli::unknown_mode::stop) && !scan.more ())
+                break;
+
+              const char* a (scan.peek ());
+
+              // Handle -I<dir>
+              //
+              if (a[0] == '-' && a[1] == 'I')
+              {
+                try
+                {
+                  ops.include_path ().push_back (dir_path (a + 2));
+                }
+                catch (const invalid_path&)
+                {
+                  throw cli::invalid_value ("-I", a + 2);
+                }
+
+                scan.next ();
+                continue;
+              }
+
+#if 0
+              // Handle --byproduct in the wrong place.
+              //
+              if (strcmp (a, "--byproduct") == 0)
+                fail (ll) << "depdb dyndep: --byproduct must be first option";
+#endif
+
+              // Handle unknown option.
+              //
+              if (a[0] == '-')
+                throw cli::unknown_option (a);
+
+              // Handle unexpected argument.
+              //
+              fail (ll) << "depdb dyndep: unexpected argument '" << a << "'";
+            }
+          }
+          catch (const cli::exception& e)
+          {
+            fail (ll) << "depdb dyndep: " << e;
+          }
         }
 
-        // Parse the options.
+        // Get the default prerequisite type falling back to file{} if not
+        // specified.
         //
-        depdb_dep_options ops;
-        try
+        // The reason one would want to specify it is to make sure different
+        // rules "resolve" the same dynamic prerequisites to the same targets.
+        // For example, a rule that implements custom C compilation for some
+        // translation unit would want to make sure it resolves extracted
+        // system headers to h{} targets analogous to the c module's rule.
+        //
+        const target_type* def_pt;
+        if (ops.default_prereq_type_specified ())
         {
-          cli::vector_scanner scan (args);
-          ops = depdb_dep_options (scan);
+          const string& t (ops.default_prereq_type ());
 
-          if (scan.more ())
-            fail (ll) << "depdb pre-dynamic: unexpected argument '"
-                      << scan.next () << "'";
-        }
-        catch (const cli::exception& e)
-        {
-          fail (ll) << "depdb pre-dynamic: " << e;
+          def_pt = bs.find_target_type (t);
+          if (def_pt == nullptr)
+            fail (ll) << "unknown target type '" << t << "'";
         }
+        else
+          def_pt = &file::static_type;
 
         // This code is based on the prior work in the cc module (specifically
         // extract_headers()) where you can often find more detailed rationale
         // for some of the steps performed.
 
+        using dyndep = dyndep_rule;
+
+        // Build the maps lazily, only if/when needed.
+        //
+        using prefix_map = dyndep::prefix_map;
+        using srcout_map = dyndep::srcout_map;
+
+        function<dyndep::map_extension_func> map_ext (
+          [] (const scope& bs, const string& n, const string& e)
+          {
+            // @@ TODO: allow specifying base target types.
+            //
+            // Feels like the only reason one would want to specify base types
+            // is to tighten things up (as opposed to making some setup work)
+            // since it essentially restricts the set of registered target
+            // types that we will consider.
+            //
+            // Note also that these would be this project's target types while
+            // the file could be from another project.
+            //
+            return dyndep::map_extension (bs, n, e, nullptr);
+
+            // @@ TODO: should we return something as fallback (file{},
+            //    def_pt)? Note: not the same semantics as enter_file()'s
+            //    fallback. Feels like it could conceivably be different
+            //    (e.g., h{} for fallback and hxx{} for some "unmappable" gen
+            //    header). It looks like the "best" way currently is to define
+            //    a custom target types for it (see moc{} in libQt5Core).
+            //
+            //    Note also that we should only do this if bs is in our
+            //    project.
+          });
+
+        // Don't we want to insert a "local"/prefixless mapping in case the
+        // user did not specify any -I's?  But then will also need src-out
+        // remapping. So it will be equivalent to -I$out_base -I$src_base? But
+        // then it's not hard to add explicitly...
+        //
+        function<dyndep::prefix_map_func> pfx_map;
+
+        struct
+        {
+          tracer& trace;
+          const location& ll;
+          const depdb_dep_options& ops;
+          optional<prefix_map> map;
+        } pfx_data {trace, ll, ops, nullopt};
+
+        if (!ops.include_path ().empty ())
+        {
+          pfx_map = [this, &pfx_data] (action,
+                                       const scope& bs,
+                                       const target& t) -> const prefix_map&
+          {
+            if (!pfx_data.map)
+            {
+              pfx_data.map = prefix_map ();
+
+              const scope& rs (*bs.root_scope ());
+
+              for (dir_path d: pfx_data.ops.include_path ())
+              {
+                if (d.relative ())
+                  fail (pfx_data.ll) << "depdb dyndep: relative include "
+                                     << "search path " << d;
+
+                if (!d.normalized (false /* canonical dir seperators */))
+                  d.normalize ();
+
+                // If we are not inside our project root, then ignore.
+                //
+                if (d.sub (rs.out_path ()))
+                  dyndep::append_prefix (
+                    pfx_data.trace, *pfx_data.map, t, move (d));
+              }
+            }
+
+            return *pfx_data.map;
+          };
+        }
+
+        optional<path> file;
+        enum class format {make} fmt (format::make);
+        command_expr cmd;
+        srcout_map so_map;
+
+        // Parse the remainder of the command line as a program (which can be
+        // a pipe). If file is absent, then we save the command's stdout to a
+        // pipe. Otherwise, assume the command writes to file and add it to
+        // the cleanups.
+        //
+        // Note that MSVC /showInclude sends its output to stderr (and so
+        // could do other broken tools). However, the user can always merge
+        // stderr to stdout (2>&1).
+        //
+        auto init_run = [this, &ctx,
+                         &lt, &ltt, &ll,
+                         &ops, prog, &file, &cmd, &so_map] ()
+        {
+          // --format
+          //
+          if (ops.format_specified ())
+          {
+            const string& f (ops.format ());
+
+            if (f != "make")
+              fail (ll) << "depdb dyndep: invalid --format option value '"
+                        << f << "'";
+          }
+
+          // --file
+          //
+          if (ops.file_specified ())
+          {
+            file = move (ops.file ());
+
+            if (file->relative ())
+              fail (ll) << "depdb dyndep: relative path specified with --file";
+          }
+
+          // Populate the srcout map with the -I$out_base -I$src_base pairs.
+          //
+          {
+            dyndep::srcout_builder builder (ctx, so_map);
+
+            for (dir_path d: ops.include_path ())
+              builder.next (move (d));
+          }
+
+          if (prog)
+          {
+            cmd = parse_command_line (lt, static_cast<token_type&> (ltt));
+
+            // If the output goes to stdout, then this should be a single
+            // pipeline without any logical operators (&& or ||).
+            //
+            if (!file && cmd.size () != 1)
+              fail (ll) << "depdb dyndep: command with stdout output cannot "
+                        << "contain logical operators";
+
+            // Note that we may need to run this command multiple times. The
+            // two potential issues here are the re-registration of the
+            // clenups and re-use of the special files (stdin, stdout, etc;
+            // they include the line index in their names to avoid clashes
+            // between lines).
+            //
+            // Cleanups are not an issue, they will simply replaced. And
+            // overriding the contents of the special files seems harmless and
+            // consistent with what would happen if the command redirects its
+            // output to a non-special file.
+            //
+            if (file)
+              environment_->clean (
+                {build2::script::cleanup_type::always, *file},
+                true /* implicit */);
+          }
+          else
+          {
+            // Assume file is one of the prerequisites.
+            //
+            if (!file)
+              fail (ll) << "depdb dyndep: program or --file expected";
+          }
+        };
+
+        // Enter as a target, update, and add to the list of prerequisite
+        // targets a file.
+        //
+        const char* what (ops.what_specified ()
+                          ? ops.what ().c_str ()
+                          : "file");
+
+        size_t skip_count (0);
+        auto add = [this, &trace, what,
+                    a, &bs, &t,
+                    &map_ext, def_pt, &pfx_map, &so_map,
+                    &dd, &skip_count] (path fp,
+                                       bool cache,
+                                       timestamp mt) -> optional<bool>
+        {
+          context& ctx (t.ctx);
+
+          // We can only defer the failure if we will be running the recipe
+          // body.
+          //
+          auto fail = [this, what, &ctx] (const auto& f) -> optional<bool>
+          {
+            bool df (!ctx.match_only && !ctx.dry_run_option);
+
+            diag_record dr;
+            dr << error << what << ' ' << f << " not found and no rule to "
+               << "generate it";
+
+            if (df)
+              dr << info << "failure deferred to recipe body diagnostics";
+
+            if (verb < 4)
+              dr << info << "re-run with --verbose=4 for more information";
+
+            if (df)
+              return nullopt;
+            else
+              dr << endf;
+          };
+
+          if (const build2::file* ft = dyndep::enter_file (
+                trace, what,
+                a, bs, t,
+                move (fp), cache, false /* normalize */,
+                map_ext, *def_pt, pfx_map, so_map).first)
+          {
+            if (optional<bool> u = dyndep::inject_file (
+                  trace, what,
+                  a, t,
+                  *ft, mt, false /* fail */))
+            {
+              if (!cache)
+                dd.expect (ft->path ());
+
+              skip_count++;
+              return *u;
+            }
+            else if (cache)
+            {
+              dd.write (); // Invalidate this line.
+              return true;
+            }
+            else
+              return fail (*ft);
+          }
+          else
+            return fail (fp);
+        };
+
         // If things go wrong (and they often do in this area), give the user
         // a bit extra context.
         //
         auto df = make_diag_frame (
-          [this, &tgt](const diag_record& dr)
+          [this, &ll, &t] (const diag_record& dr)
           {
             if (verb != 0)
-              dr << info << "while extracting dynamic dependencies for " << tgt;
+              dr << info (ll) << "while extracting dynamic dependencies for "
+                 << t;
           });
 
         // If nothing so far has invalidated the dependency database, then try
         // the cached data before running the program.
         //
         bool cache (!update);
-        size_t skip_count (0);
 
-        for (bool restart (true); restart; cache = false)
+        for (bool restart (true), first_run (true); restart; cache = false)
         {
           restart = false;
 
@@ -1314,62 +1635,212 @@ namespace build2
 
               if (l->empty ()) // Done, nothing changed.
                 return;
+
+              if (optional<bool> r = add (path (move (*l)), true /*cache*/, mt))
+              {
+                restart = *r;
+
+                if (restart)
+                {
+                  update = true;
+                  l6 ([&]{trace << "restarting (cache)";});
+                  break;
+                }
+              }
+              else
+              {
+                // Trigger rebuild and mark as expected to fail.
+                //
+                update = true;
+                deferred_failure = true;
+                return;
+              }
             }
           }
           else
           {
-          }
-        }
+            if (first_run)
+            {
+              init_run ();
+              first_run = false;
+            }
+            else if (!prog)
+            {
+              fail (ll) << "generated " << what << " without program to retry";
+            }
 
-        optional<path> file;
-        if (ops.file_specified ())
-        {
-          file = path (ops.file ()); // @@ TMP path
+            // Save the timestamp just before we run the command. If we depend
+            // on any file that has been updated since, then we should assume
+            // we have "seen" the old copy and restart.
+            //
+            timestamp rmt (prog ? system_clock::now () : mt);
 
-          // @@ TODO: file must be absolute.
-        }
+            // Run the command if any and reduce outputs to common istream.
+            //
+            // Note that the resulting stream should tolerate partial read.
+            //
+            // While reading the entire stdout into a string is not the most
+            // efficient way to do it, this does simplify things quite a bit,
+            // not least of which is not having to parse the output before
+            // knowing the program exist status.
+            //
+            istringstream iss;
+            if (prog)
+            {
+              string s;
+              build2::script::run (*environment_,
+                                   cmd,
+                                   li,
+                                   ll,
+                                   !file ? &s : nullptr);
+
+              if (!file)
+              {
+                iss.str (move (s));
+                iss.exceptions (istream::badbit);
+              }
+            }
 
-        if (prog)
-        {
-          // Run the remainder of the command line as a program (which can be
-          // a pipe). If file is absent, then redirect the command's stdout to
-          // a pipe. Otherwise, assume the command writes to a file and add it
-          // to the cleanups. @@ TODO: reword
-          //
-          // Note that MSVC /showInclude sends its output to stderr (and so
-          // could do other broken tools). However, the user can always merge
-          // stderr to stdout (2>&1).
-          //
-          command_expr ce (
-            parse_command_line (t, static_cast<token_type&> (tt)));
+            ifdstream ifs (ifdstream::badbit);
+            if (file)
+            try
+            {
+              ifs.open (*file);
+            }
+            catch (const io_error& e)
+            {
+              fail (ll) << "unable to open file " << *file << ": " << e;
+            }
 
-          // If the output goes to stdout, then this should be a single
-          // pipeline without any logical operators (&& or ||).
-          //
-          // @@ TODO: improve diagnostics.
-          //
-          if (!file && ce.size () != 1)
-            fail (ll) << "depdb pre-dynamic: command cannot contain "
-                      << "logical operators";
-
-          string s;
-          build2::script::run (*environment_,
-                               ce,
-                               li,
-                               ll,
-                               !file ? &s : nullptr);
-
-          if (file)
-            environment_->clean ({build2::script::cleanup_type::always, *file},
-                                 true /* implicit */);
-        }
-        else
-        {
-          // Assume file is one of the prerequisites.
-          //
-          if (!file)
-            fail (ll) << "depdb pre-dynamic: program or --file expected";
+            istream& is (file
+                         ? static_cast<istream&> (ifs)
+                         : static_cast<istream&> (iss));
+
+            const path_name& in (file
+                                 ? path_name (*file)
+                                 : path_name ("<stdin>"));
+
+            location il (in, 1);
+
+            // The way we parse things is format-specific.
+            //
+            size_t skip (skip_count);
+
+            switch (fmt)
+            {
+            case format::make:
+              {
+                using make_state = make_parser;
+                using make_type = make_parser::type;
+
+                make_parser make;
+
+                for (string l; !restart; ++il.line) // Reuse the buffer.
+                {
+                  if (eof (getline (is, l)))
+                  {
+                    if (make.state != make_state::end)
+                      fail (il) << "incomplete make dependency declaration";
+
+                    break;
+                  }
+
+                  size_t pos (0);
+                  do
+                  {
+                    pair<make_type, string> r;
+                    {
+                      auto df = make_diag_frame (
+                        [this, &l] (const diag_record& dr)
+                        {
+                          if (verb != 0)
+                            dr << info << "while parsing make dependency "
+                               << "declaration line '" << l << "'";
+                        });
+
+                      r = make.next (l, pos, il, false /* strict */);
+                    }
+
+                    if (r.second.empty ())
+                      continue;
+
+                    // @@ TODO: what should we do about targets?
+                    //
+                    // Note that if we take GCC as an example, things are
+                    // quite messed up: by default it ignores -o and just
+                    // takes the source file name and replaces the extension
+                    // with a platform-appropriate object file extension. One
+                    // can specify a custom target (or even multiple targets)
+                    // with -MT or with -MQ (quoting). Though MinGW GCC still
+                    // does not quote `:` with -MQ. So in this case it's
+                    // definitely easier for the user to ignore the targets
+                    // and just specify everything in the buildfile.
+                    //
+                    // On the other hand, other tools are likely to produce
+                    // more sensible output (except perhaps for quoting).
+                    //
+                    // @@ Maybe in the lax mode we should only recognize `:`
+                    //    if it's separated on at least one side?
+                    //
+                    //    Alternatively, we could detect Windows drives in
+                    //    paths and "handle" them (I believe this is what GNU
+                    //    make does). Maybe we should have three formats:
+                    //    make-lax, make, make-strict?
+                    //
+                    if (r.first == make_type::target)
+                      continue;
+
+                    // Skip until where we left off.
+                    //
+                    if (skip != 0)
+                    {
+                      skip--;
+                      continue;
+                    }
+
+                    if (optional<bool> u = add (path (move (r.second)),
+                                                false /* cache */,
+                                                rmt))
+                    {
+                      restart = *u;
+
+                      if (restart)
+                      {
+                        update = true;
+                        l6 ([&]{trace << "restarting";});
+                        break;
+                      }
+                    }
+                    else
+                    {
+                      // Trigger recompilation, mark as expected to fail, and
+                      // bail out.
+                      //
+                      update = true;
+                      deferred_failure = true;
+                      break;
+                    }
+                  }
+                  while (pos != l.size ());
+
+                  if (make.state == make_state::end || deferred_failure)
+                    break;
+                }
+
+                break;
+              }
+            }
+
+            // Bail out early if we have deferred a failure.
+            //
+            if (deferred_failure)
+              return;
+          }
         }
+
+        // Add the terminating blank line (we are updating depdb).
+        //
+        dd.expect ("");
       }
 
       // When add a special variable don't forget to update lexer::word().
diff --git a/libbuild2/build/script/parser.hxx b/libbuild2/build/script/parser.hxx
index f957f82..da15509 100644
--- a/libbuild2/build/script/parser.hxx
+++ b/libbuild2/build/script/parser.hxx
@@ -81,13 +81,16 @@ namespace build2
         // initialize/clean up the environment before/after the script
         // execution.
         //
+        // Note: having both root and base scopes for testing (where we pass
+        // global scope for both).
+        //
         void
-        execute_body (const scope& base,
+        execute_body (const scope& root, const scope& base,
                       environment&, const script&, runner&,
                       bool enter = true, bool leave = true);
 
 
-        // Execute the first or the second (pre-dynamic) half of the depdb
+        // Execute the first or the second (dyndep) half of the depdb
         // preamble.
         //
         // Note that it's the caller's responsibility to make sure that the
@@ -95,33 +98,33 @@ namespace build2
         // command execution and leave() -- after the last command.
         //
         void
-        execute_depdb_preamble (const scope& base,
+        execute_depdb_preamble (action a, const scope& base, const file& t,
                                 environment& e, const script& s, runner& r,
                                 depdb& dd)
         {
           auto b (s.depdb_preamble.begin ());
           exec_depdb_preamble (
-            base,
+            a, base, t,
             e, s, r,
             b,
-            (s.depdb_pre_dynamic
-             ? b + *s.depdb_pre_dynamic
+            (s.depdb_dyndep
+             ? b + *s.depdb_dyndep
              : s.depdb_preamble.end ()),
             dd);
         }
 
         void
-        execute_depdb_preamble_dynamic (
-          const scope& base,
+        execute_depdb_preamble_dyndep (
+          action a, const scope& base, file& t,
           environment& e, const script& s, runner& r,
-          depdb& dd, bool& update, timestamp mt)
+          depdb& dd, bool& update, bool& deferred_failure, timestamp mt)
         {
           exec_depdb_preamble (
-            base,
+            a, base, t,
             e, s, r,
-            s.depdb_preamble.begin () + *s.depdb_pre_dynamic,
+            s.depdb_preamble.begin () + *s.depdb_dyndep,
             s.depdb_preamble.end (),
-            dd, &update, mt);
+            dd, &update, &deferred_failure, mt);
         }
 
         // Parse a special builtin line into names, performing the variable
@@ -129,7 +132,7 @@ namespace build2
         // builtin name from the result.
         //
         names
-        execute_special (const scope& base,
+        execute_special (const scope& root, const scope& base,
                          environment&,
                          const line&,
                          bool omit_builtin = true);
@@ -157,20 +160,22 @@ namespace build2
         exec_special (token&, build2::script::token_type&, bool skip_first);
 
         void
-        exec_depdb_preamble (const scope& base,
+        exec_depdb_preamble (action, const scope& base, const file&,
                              environment&, const script&, runner&,
                              lines_iterator begin, lines_iterator end,
                              depdb&,
                              bool* update = nullptr,
+                             bool* deferred_failure = nullptr,
                              optional<timestamp> mt = nullopt);
 
         void
-        exec_depdb_pre_dynamic (token&, build2::script::token_type&,
-                                size_t line_index, const location&,
-                                const target&,
-                                depdb&,
-                                bool& update,
-                                timestamp);
+        exec_depdb_dyndep (token&, build2::script::token_type&,
+                           size_t line_index, const location&,
+                           action, const scope& base, file&,
+                           depdb&,
+                           bool& update,
+                           bool& deferred_failure,
+                           timestamp);
 
         // Helpers.
         //
@@ -269,13 +274,13 @@ namespace build2
         // depdb env <var-names> - Track the environment variables change as a
         //                         hash.
         //
-        // depdb pre-dynamic ... - Extract dynamic dependency information.
+        // depdb dyndep ...      - Extract dynamic dependency information.
         //                         Can only be the last depdb builtin call
         //                         in the preamble.
         //
         optional<location> depdb_clear_;    // depdb-clear location.
         optional<pair<location, size_t>>
-          depdb_pre_dynamic_;               // depdb-pre-dynamic location.
+                           depdb_dyndep_;   // depdb-dyndep location/position.
         lines              depdb_preamble_; // Note: excluding depdb-clear.
 
         // If present, the first impure function called in the body of the
diff --git a/libbuild2/build/script/script.hxx b/libbuild2/build/script/script.hxx
index bdfbe51..9d7567c 100644
--- a/libbuild2/build/script/script.hxx
+++ b/libbuild2/build/script/script.hxx
@@ -75,7 +75,7 @@ namespace build2
         // script parser for details).
         //
         bool             depdb_clear;
-        optional<size_t> depdb_pre_dynamic; // Position of first pre-dynamic.
+        optional<size_t> depdb_dyndep;   // Position of first depdb-dyndep.
         lines_type       depdb_preamble;
         bool             depdb_preamble_temp_dir = false; // True if refs $~.
 
diff --git a/libbuild2/build/script/types-parsers.cxx b/libbuild2/build/script/types-parsers.cxx
new file mode 100644
index 0000000..9ecfa13
--- /dev/null
+++ b/libbuild2/build/script/types-parsers.cxx
@@ -0,0 +1,56 @@
+// file      : libbuild2/build/script/types-parsers.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/build/script/types-parsers.hxx>
+
+#include <libbuild2/build/script/builtin-options.hxx> // cli namespace
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      namespace cli
+      {
+        template <typename T>
+        static void
+        parse_path (T& x, scanner& s)
+        {
+          const char* o (s.next ());
+
+          if (!s.more ())
+            throw missing_value (o);
+
+          const char* v (s.next ());
+
+          try
+          {
+            x = T (v);
+
+            if (x.empty ())
+              throw invalid_value (o, v);
+          }
+          catch (const invalid_path&)
+          {
+            throw invalid_value (o, v);
+          }
+        }
+
+        void parser<path>::
+        parse (path& x, bool& xs, scanner& s)
+        {
+          xs = true;
+          parse_path (x, s);
+        }
+
+        void parser<dir_path>::
+        parse (dir_path& x, bool& xs, scanner& s)
+        {
+          xs = true;
+          parse_path (x, s);
+        }
+      }
+    }
+  }
+}
diff --git a/libbuild2/build/script/types-parsers.hxx b/libbuild2/build/script/types-parsers.hxx
new file mode 100644
index 0000000..a42dab7
--- /dev/null
+++ b/libbuild2/build/script/types-parsers.hxx
@@ -0,0 +1,49 @@
+// file      : libbuild2/build/script/types-parsers.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+// CLI parsers, included into the generated source files.
+//
+
+#ifndef LIBBUILD2_BUILD_SCRIPT_TYPES_PARSERS_HXX
+#define LIBBUILD2_BUILD_SCRIPT_TYPES_PARSERS_HXX
+
+#include <libbuild2/types.hxx>
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      namespace cli
+      {
+        class scanner;
+
+        template <typename T>
+        struct parser;
+
+        template <>
+        struct parser<path>
+        {
+          static void
+          parse (path&, bool&, scanner&);
+
+          static void
+          merge (path& b, const path& a) {b = a;}
+        };
+
+        template <>
+        struct parser<dir_path>
+        {
+          static void
+          parse (dir_path&, bool&, scanner&);
+
+          static void
+          merge (dir_path& b, const dir_path& a) {b = a;}
+        };
+      }
+    }
+  }
+}
+
+#endif // LIBBUILD2_BUILD_SCRIPT_TYPES_PARSERS_HXX
diff --git a/libbuild2/buildfile b/libbuild2/buildfile
index 51747fd..f21be7b 100644
--- a/libbuild2/buildfile
+++ b/libbuild2/buildfile
@@ -217,8 +217,9 @@ else
 
 # Generated options parser.
 #
-# @@ Consider generating common cli runtime namespace if adding more
-#    option files.
+# @@ Consider generating common cli runtime namespace if adding more option
+#    files. Plus sommon types-parser.?xx (which could also potentially be
+#    reused by the driver).
 #
 if $cli.configured
 {
@@ -252,7 +253,9 @@ if $cli.configured
   build/script/cli.cxx{builtin-options}: build/script/cli{builtin}
   {
     cli.options += --cli-namespace build2::build::script::cli \
---include-prefix libbuild2/build/script --guard-prefix LIBBUILD2_BUILD_SCRIPT
+--include-prefix libbuild2/build/script --guard-prefix LIBBUILD2_BUILD_SCRIPT \
+--cxx-prologue "#include <libbuild2/build/script/types-parsers.hxx>" \
+--generate-parse
   }
 }
 else
diff --git a/libbuild2/cc/compile-rule.cxx b/libbuild2/cc/compile-rule.cxx
index 5a3ed95..525821f 100644
--- a/libbuild2/cc/compile-rule.cxx
+++ b/libbuild2/cc/compile-rule.cxx
@@ -16,6 +16,7 @@
 #include <libbuild2/algorithm.hxx>
 #include <libbuild2/filesystem.hxx>  // mtime()
 #include <libbuild2/diagnostics.hxx>
+#include <libbuild2/make-parser.hxx>
 
 #include <libbuild2/bin/target.hxx>
 
@@ -707,7 +708,7 @@ namespace build2
     void compile_rule::
     append_library_prefixes (appended_libraries& ls, prefix_map& pm,
                              const scope& bs,
-                             action a, target& t, linfo li) const
+                             action a, const target& t, linfo li) const
     {
       struct data
       {
@@ -730,14 +731,21 @@ namespace build2
         if (find (d.ls.begin (), d.ls.end (), &l) != d.ls.end ())
           return false;
 
-        const variable& var (
-          com
-          ? c_export_poptions
-          : (t == x
-             ? x_export_poptions
-             : l.ctx.var_pool[t + ".export.poptions"]));
-
-        append_prefixes (d.pm, l, var);
+        // If this target does not belong to any project (e.g, an "imported as
+        // installed" library), then it can't possibly generate any headers
+        // for us.
+        //
+        if (const scope* rs = l.base_scope ().root_scope ())
+        {
+          const variable& var (
+            com
+            ? c_export_poptions
+            : (t == x
+               ? x_export_poptions
+               : l.ctx.var_pool[t + ".export.poptions"]));
+
+          append_prefixes (d.pm, *rs, l, var);
+        }
 
         if (com)
           d.ls.push_back (&l);
@@ -1486,77 +1494,13 @@ namespace build2
       }
     }
 
-    // Reverse-lookup target type(s) from extension.
-    //
-    small_vector<const target_type*, 2> compile_rule::
-    map_extension (const scope& bs, const string& n, const string& e) const
-    {
-      // We will just have to try all of the possible ones, in the "most
-      // likely to match" order.
-      //
-      auto test = [&bs, &n, &e] (const target_type& tt) -> bool
-      {
-        // Call the extension derivation function. Here we know that it will
-        // only use the target type and name from the target key so we can
-        // pass bogus values for the rest.
-        //
-        target_key tk {&tt, nullptr, nullptr, &n, nullopt};
-
-        // This is like prerequisite search.
-        //
-        optional<string> de (tt.default_extension (tk, bs, nullptr, true));
-
-        return de && *de == e;
-      };
-
-      small_vector<const target_type*, 2> r;
-
-      for (const target_type* const* p (x_inc); *p != nullptr; ++p)
-        if (test (**p))
-          r.push_back (*p);
-
-      // Next try target types derived from any of the C-source types.
-      //
-      const target_type_map& ttm (bs.root_scope ()->root_extra->target_types);
-
-      for (auto i (ttm.type_begin ()), e (ttm.type_end ()); i != e; ++i)
-      {
-        const target_type& dt (i->second);
-
-        for (const target_type* const* p (x_inc); *p != nullptr; ++p)
-        {
-          const target_type& bt (**p);
-
-          if (dt.is_a (bt))
-          {
-            if (dt != bt && test (dt))
-              r.push_back (&dt);
-
-            break;
-          }
-        }
-      }
-
-      return r;
-    }
-
     void compile_rule::
-    append_prefixes (prefix_map& m, const target& t, const variable& var) const
+    append_prefixes (prefix_map& m,
+                     const scope& rs, const target& t,
+                     const variable& var) const
     {
       tracer trace (x, "compile_rule::append_prefixes");
 
-      // If this target does not belong to any project (e.g, an "imported as
-      // installed" library), then it can't possibly generate any headers for
-      // us.
-      //
-      const scope& bs (t.base_scope ());
-      const scope* rs (bs.root_scope ());
-      if (rs == nullptr)
-        return;
-
-      const dir_path& out_base (t.dir);
-      const dir_path& out_root (rs->out_path ());
-
       if (auto l = t[var])
       {
         const auto& v (cast<strings> (l));
@@ -1614,136 +1558,8 @@ namespace build2
 
           // If we are not inside our project root, then ignore.
           //
-          if (!d.sub (out_root))
-            continue;
-
-          // If the target directory is a sub-directory of the include
-          // directory, then the prefix is the difference between the
-          // two. Otherwise, leave it empty.
-          //
-          // The idea here is to make this "canonical" setup work auto-
-          // magically:
-          //
-          // 1. We include all files with a prefix, e.g., <foo/bar>.
-          // 2. The library target is in the foo/ sub-directory, e.g.,
-          //    /tmp/foo/.
-          // 3. The poptions variable contains -I/tmp.
-          //
-          dir_path p (out_base.sub (d) ? out_base.leaf (d) : dir_path ());
-
-          // We use the target's directory as out_base but that doesn't work
-          // well for targets that are stashed in subdirectories. So as a
-          // heuristics we are going to also enter the outer directories of
-          // the original prefix. It is, however, possible, that another -I
-          // option after this one will produce one of these outer prefixes as
-          // its original prefix in which case we should override it.
-          //
-          // So we are going to assign the original prefix priority value 0
-          // (highest) and then increment it for each outer prefix.
-          //
-          auto enter = [&trace, &m] (dir_path p, dir_path d, size_t prio)
-          {
-            auto j (m.lower_bound (p)), e (m.end ());
-
-            if (j != e && j->first != p)
-              j = e;
-
-            if (j == m.end ())
-            {
-              if (verb >= 4)
-                trace << "new mapping for prefix '" << p << "'\n"
-                      << "  new mapping to      " << d << " priority " << prio;
-
-              m.emplace (move (p), prefix_value {move (d), prio});
-            }
-            else if (p.empty ())
-            {
-              // For prefixless we keep all the entries since for them we have
-              // an extra check (target must be explicitly spelled out in a
-              // buildfile).
-              //
-              if (verb >= 4)
-                trace << "additional mapping for prefix '" << p << "'\n"
-                      << "  new mapping to      " << d << " priority " << prio;
-
-              // Find the position where to insert according to the priority.
-              // For equal priorities we use the insertion order.
-              //
-              do
-              {
-                if (j->second.priority > prio)
-                  break;
-              }
-              while (++j != e && j->first == p);
-
-              m.emplace_hint (j, move (p), prefix_value {move (d), prio});
-            }
-            else
-            {
-              prefix_value& v (j->second);
-
-              // We used to reject duplicates but it seems this can be
-              // reasonably expected to work according to the order of the
-              // -I options.
-              //
-              // Seeing that we normally have more "specific" -I paths first,
-              // (so that we don't pick up installed headers, etc), we ignore
-              // it.
-              //
-              if (v.directory == d)
-              {
-                if (v.priority > prio)
-                  v.priority = prio;
-              }
-              else if (v.priority <= prio)
-              {
-                if (verb >= 4)
-                  trace << "ignoring mapping for prefix '" << p << "'\n"
-                        << "  existing mapping to " << v.directory
-                        << " priority " << v.priority << '\n'
-                        << "  another mapping to  " << d
-                        << " priority " << prio;
-              }
-              else
-              {
-                if (verb >= 4)
-                  trace << "overriding mapping for prefix '" << p << "'\n"
-                        << "  existing mapping to " << v.directory
-                        << " priority " << v.priority << '\n'
-                        << "  new mapping to      " << d
-                        << " priority " << prio;
-
-                v.directory = move (d);
-                v.priority = prio;
-              }
-            }
-          };
-
-#if 1
-          // Enter all outer prefixes, including prefixless.
-          //
-          // The prefixless part is fuzzy but seems to be doing the right
-          // thing ignoring/overriding-wise, at least in cases where one of
-          // the competing -I paths is a subdirectory of another.
-          //
-          for (size_t prio (0);; ++prio)
-          {
-            bool e (p.empty ());
-            enter ((e ? move (p) : p), (e ? move (d) : d), prio);
-            if (e)
-              break;
-            p = p.directory ();
-          }
-#else
-          size_t prio (0);
-          for (bool e (false); !e; ++prio)
-          {
-            dir_path n (p.directory ());
-            e = n.empty ();
-            enter ((e ? move (p) : p), (e ? move (d) : d), prio);
-            p = move (n);
-          }
-#endif
+          if (d.sub (rs.out_path ()))
+            append_prefix (trace, m, t, move (d));
         }
       }
     }
@@ -1751,15 +1567,16 @@ namespace build2
     auto compile_rule::
     build_prefix_map (const scope& bs,
                       action a,
-                      target& t,
+                      const target& t,
                       linfo li) const -> prefix_map
     {
       prefix_map pm;
 
       // First process our own.
       //
-      append_prefixes (pm, t, x_poptions);
-      append_prefixes (pm, t, c_poptions);
+      const scope& rs (*bs.root_scope ());
+      append_prefixes (pm, rs, t, x_poptions);
+      append_prefixes (pm, rs, t, c_poptions);
 
       // Then process the include directories from prerequisite libraries.
       //
@@ -1769,6 +1586,9 @@ namespace build2
       return pm;
     }
 
+    // @@ TMP
+    //
+#if 0
     // Return the next make prerequisite starting from the specified
     // position and update position to point to the start of the
     // following prerequisite or l.size() if there are none left.
@@ -1830,6 +1650,7 @@ namespace build2
 
       return r;
     }
+#endif
 
     // VC /showIncludes output. The first line is the file being compiled
     // (unless clang-cl; handled by our caller). Then we have the list of
@@ -2251,7 +2072,7 @@ namespace build2
                 if (verb > 2)
                 {
                   diag_record dr;
-                  dr << error << "header '" << f << "' not found and no "
+                  dr << error << "header " << f << " not found and no "
                      << "rule to generate it";
 
                   if (verb < 4)
@@ -2970,355 +2791,56 @@ namespace build2
     }
 #endif
 
-    // Enter as a target a header file. Depending on the cache flag, the file
-    // is assumed to either have come from the depdb cache or from the
-    // compiler run.
-    //
-    // Return the header target and an indication of whether it was remapped
-    // or NULL if the header does not exist and cannot be generated. In the
-    // latter case the passed header path is guaranteed to be still valid but
-    // might have been adjusted (e.g., normalized, etc).
-    //
     // Note: this used to be a lambda inside extract_headers() so refer to the
     // body of that function for the overall picture.
     //
     pair<const file*, bool> compile_rule::
     enter_header (action a, const scope& bs, file& t, linfo li,
                   path&& f, bool cache, bool norm,
-                  optional<prefix_map>& pfx_map, srcout_map& so_map) const
+                  optional<prefix_map>& pfx_map,
+                  const srcout_map& so_map) const
     {
       tracer trace (x, "compile_rule::enter_header");
 
-      // Find or maybe insert the target. The directory is only moved from if
-      // insert is true. Note that it must be normalized.
-      //
-      auto find = [&trace, &t, this] (dir_path&& d,
-                                      path&& f,
-                                      bool insert) -> const file*
-      {
-        // Split the file into its name part and extension. Here we can assume
-        // the name part is a valid filesystem name.
-        //
-        // Note that if the file has no extension, we record an empty
-        // extension rather than NULL (which would signify that the default
-        // extension should be added).
-        //
-        string e (f.extension ());
-        string n (move (f).string ());
-
-        if (!e.empty ())
-          n.resize (n.size () - e.size () - 1); // One for the dot.
-
-        // See if this directory is part of any project and if so determine
-        // the target type.
-        //
-        // While at it also determine if this target is from the src or out
-        // tree of said project.
-        //
-        dir_path out;
-
-        // It's possible the extension-to-target type mapping is ambiguous
-        // (usually because both C and X-language headers use the same .h
-        // extension). In this case we will first try to find one that matches
-        // an explicit target (similar logic to when insert is false).
-        //
-        small_vector<const target_type*, 2> tts;
-
-        // Note that the path can be in out or src directory and the latter
-        // can be associated with multiple scopes. So strictly speaking we
-        // need to pick one that is "associated" with us. But that is still a
-        // TODO (see scope_map::find() for details) and so for now we just
-        // pick the first one (it's highly unlikely the source file extension
-        // mapping will differ based on the configuration).
-        //
-        {
-          const scope& bs (**t.ctx.scopes.find (d).first);
-          if (const scope* rs = bs.root_scope ())
-          {
-            tts = map_extension (bs, n, e);
-
-            if (!bs.out_eq_src () && d.sub (bs.src_path ()))
-              out = out_src (d, *rs);
-          }
-        }
-
-        // If it is outside any project, or the project doesn't have such an
-        // extension, assume it is a plain old C header.
-        //
-        if (tts.empty ())
-        {
-          // If the project doesn't "know" this extension then we can't
-          // possibly find an explicit target of this type.
-          //
-          if (!insert)
-          {
-            l6 ([&]{trace << "unknown header " << n << " extension '"
-                          << e << "'";});
-            return nullptr;
-          }
-
-          tts.push_back (&h::static_type);
-        }
-
-        // Find or insert target.
-        //
-        // Note that in case of the target type ambiguity we first try to find
-        // an explicit target that resolves this ambiguity.
-        //
-        const target* r (nullptr);
-
-        if (!insert || tts.size () > 1)
-        {
-          // Note that we skip any target type-specific searches (like for an
-          // existing file) and go straight for the target object since we
-          // need to find the target explicitly spelled out.
-          //
-          // Also, it doesn't feel like we should be able to resolve an
-          // absolute path with a spelled-out extension to multiple targets.
-          //
-          for (const target_type* tt: tts)
-          {
-            if ((r = t.ctx.targets.find (*tt, d, out, n, e, trace)) != nullptr)
-              break;
-            else
-              l6 ([&]{trace << "no targe with target type " << tt->name;});
-          }
-
-          // Note: we can't do this because of the in-source builds where
-          // there won't be explicit targets for non-generated headers.
-          //
-          // This should be harmless, however, since in our world generated
-          // headers are normally spelled-out as explicit targets. And if not,
-          // we will still get an error, just a bit less specific.
-          //
-#if 0
-          if (r == nullptr && insert)
-          {
-            f = d / n;
-            if (!e.empty ())
-            {
-              f += '.';
-              f += e;
-            }
-
-            diag_record dr (fail);
-            dr << "mapping of header " << f << " to target type is ambiguous";
-            for (const target_type* tt: tts)
-              dr << info << "could be " << tt->name << "{}";
-            dr << info << "spell-out its target to resolve this ambiguity";
-          }
-#endif
-        }
-
-        // @@ OPT: move d, out, n
-        //
-        if (r == nullptr && insert)
-          r = &search (t, *tts[0], d, out, n, &e, nullptr);
-
-        return static_cast<const file*> (r);
-      };
-
-      // If it's not absolute then it either does not (yet) exist or is a
-      // relative ""-include (see init_args() for details). Reduce the second
-      // case to absolute.
-      //
-      // Note: we now always use absolute path to the translation unit so this
-      // no longer applies. But let's keep it for posterity.
-      //
-#if 0
-      if (f.relative () && rels.relative ())
-      {
-        // If the relative source path has a directory component, make sure
-        // it matches since ""-include will always start with that (none of
-        // the compilers we support try to normalize this path). Failed that
-        // we may end up searching for a generated header in a random
-        // (working) directory.
-        //
-        const string& fs (f.string ());
-        const string& ss (rels.string ());
-
-        size_t p (path::traits::rfind_separator (ss));
-
-        if (p == string::npos || // No directory.
-            (fs.size () > p + 1 &&
-             path::traits::compare (fs.c_str (), p, ss.c_str (), p) == 0))
-        {
-          path t (work / f); // The rels path is relative to work.
-
-          if (exists (t))
-            f = move (t);
-        }
-      }
-#endif
-
-      const file* pt (nullptr);
-      bool remapped (false);
-
-      // If still relative then it does not exist.
-      //
-      if (f.relative ())
-      {
-        // This is probably as often an error as an auto-generated file, so
-        // trace at level 4.
-        //
-        l4 ([&]{trace << "non-existent header '" << f << "'";});
-
-        f.normalize ();
-
-        // The relative path might still contain '..' (e.g., ../foo.hxx;
-        // presumably ""-include'ed). We don't attempt to support auto-
-        // generated headers with such inclusion styles.
-        //
-        if (f.normalized ())
-        {
-          if (!pfx_map)
-            pfx_map = build_prefix_map (bs, a, t, li);
-
-          // First try the whole file. Then just the directory.
-          //
-          // @@ Has to be a separate map since the prefix can be the same as
-          //    the file name.
-          //
-          // auto i (pfx_map->find (f));
-
-          // Find the most qualified prefix of which we are a sub-path.
-          //
-          if (!pfx_map->empty ())
-          {
-            dir_path d (f.directory ());
-            auto p (pfx_map->sup_range (d));
-
-            if (p.first != p.second)
-            {
-              // Note that we can only have multiple entries for the
-              // prefixless mapping.
-              //
-              dir_path pd; // Reuse.
-              for (auto i (p.first); i != p.second; ++i)
-              {
-                // Note: value in pfx_map is not necessarily canonical.
-                //
-                pd = i->second.directory;
-                pd.canonicalize ();
-
-                l4 ([&]{trace << "try prefix '" << d << "' mapped to " << pd;});
-
-                // If this is a prefixless mapping, then only use it if we can
-                // resolve it to an existing target (i.e., it is explicitly
-                // spelled out in a buildfile). @@ Hm, I wonder why, it's not
-                // like we can generate any header without an explicit target.
-                // Maybe for diagnostics (i.e., we will actually try to build
-                // something there instead of just saying no mapping).
-                //
-                pt = find (pd / d, f.leaf (), !i->first.empty ());
-                if (pt != nullptr)
-                {
-                  f = pd / f;
-                  l4 ([&]{trace << "mapped as auto-generated " << f;});
-                  break;
-                }
-                else
-                  l4 ([&]{trace << "no explicit target in " << pd;});
-              }
-            }
-            else
-              l4 ([&]{trace << "no prefix map entry for '" << d << "'";});
-          }
-          else
-            l4 ([&]{trace << "prefix map is empty";});
-        }
-      }
-      else
+      struct data
       {
-        // Normalize the path unless it comes from the depdb, in which case
-        // we've already done that (normally). This is also where we handle
-        // src-out remap (again, not needed if cached).
-        //
-        if (!cache || norm)
-          normalize_header (f);
-
-        if (!cache)
+        linfo li;
+        optional<prefix_map>& pfx_map;
+      } d {li, pfx_map};
+
+      // If it is outside any project, or the project doesn't have such an
+      // extension, assume it is a plain old C header.
+      //
+      return enter_file (
+        trace, "header",
+        a, bs, t,
+        move (f), cache, norm,
+        [this] (const scope& bs, const string& n, const string& e)
         {
-          if (!so_map.empty ())
-          {
-            // Find the most qualified prefix of which we are a sub-path.
-            //
-            auto i (so_map.find_sup (f));
-            if (i != so_map.end ())
-            {
-              // Ok, there is an out tree for this headers. Remap to a path
-              // from the out tree and see if there is a target for it. Note
-              // that the value in so_map is not necessarily canonical.
-              //
-              dir_path d (i->second);
-              d /= f.leaf (i->first).directory ();
-              d.canonicalize ();
-
-              pt = find (move (d), f.leaf (), false); // d is not moved from.
-
-              if (pt != nullptr)
-              {
-                path p (d / f.leaf ());
-                l4 ([&]{trace << "remapping " << f << " to " << p;});
-                f = move (p);
-                remapped = true;
-              }
-            }
-          }
-        }
-
-        if (pt == nullptr)
+          return map_extension (bs, n, e, x_inc);
+        },
+        h::static_type,
+        [this, &d] (action a, const scope& bs, const target& t)
+          -> const prefix_map&
         {
-          l6 ([&]{trace << "entering " << f;});
-          pt = find (f.directory (), f.leaf (), true);
-        }
-      }
+          if (!d.pfx_map)
+            d.pfx_map = build_prefix_map (bs, a, t, d.li);
 
-      return make_pair (pt, remapped);
+          return *d.pfx_map;
+        },
+        so_map);
     }
 
-    // Update and add to the list of prerequisite targets a header or header
-    // unit target.
-    //
-    // Return the indication of whether it has changed or, if the passed
-    // timestamp is not timestamp_unknown, is older than the target. If the
-    // header does not exists nor can be generated (no rule), then issue
-    // diagnostics and fail if the fail argument is true and return nullopt
-    // otherwise.
-    //
     // Note: this used to be a lambda inside extract_headers() so refer to the
     // body of that function for the overall picture.
     //
     optional<bool> compile_rule::
     inject_header (action a, file& t,
-                   const file& pt, timestamp mt, bool f /* fail */) const
+                   const file& pt, timestamp mt, bool fail) const
     {
       tracer trace (x, "compile_rule::inject_header");
 
-      // Even if failing we still use try_match() in order to issue consistent
-      // (with extract_headers() below) diagnostics (rather than the generic
-      // "not rule to update ...").
-      //
-      if (!try_match (a, pt).first)
-      {
-        if (!f)
-          return nullopt;
-
-        diag_record dr;
-        dr << fail << "header " << pt << " not found and no rule to "
-           << "generate it";
-
-        if (verb < 4)
-          dr << info << "re-run with --verbose=4 for more information";
-      }
-
-      bool r (update (trace, a, pt, mt));
-
-      // Add to our prerequisite target list.
-      //
-      t.prerequisite_targets[a].push_back (&pt);
-
-      return r;
+      return inject_file (trace, "header", a, t, pt, mt, fail);
     }
 
     // Extract and inject header dependencies. Return the preprocessed source
@@ -3353,16 +2875,6 @@ namespace build2
       file_cache::entry psrc;
       bool puse (true);
 
-      // If things go wrong (and they often do in this area), give the user a
-      // bit extra context.
-      //
-      auto df = make_diag_frame (
-        [&src](const diag_record& dr)
-        {
-          if (verb != 0)
-            dr << info << "while extracting header dependencies from " << src;
-        });
-
       // Preprocesor mode that preserves as much information as possible while
       // still performing inclusions. Also serves as a flag indicating whether
       // this compiler uses the separate preprocess and compile setup.
@@ -3518,9 +3030,9 @@ namespace build2
       // generator by end-users optional by shipping pre-generated headers.
       //
       // This is a nasty problem that doesn't seem to have a perfect solution
-      // (except, perhaps, C++ modules). So what we are going to do is try to
-      // rectify the situation by detecting and automatically remapping such
-      // mis-inclusions. It works as follows.
+      // (except, perhaps, C++ modules and/or module mapper). So what we are
+      // going to do is try to rectify the situation by detecting and
+      // automatically remapping such mis-inclusions. It works as follows.
       //
       // First we will build a map of src/out pairs that were specified with
       // -I. Here, for performance and simplicity, we will assume that they
@@ -3533,10 +3045,7 @@ namespace build2
       // case, then we calculate a corresponding header in the out tree and,
       // (this is the most important part), check if there is a target for
       // this header in the out tree. This should be fairly accurate and not
-      // require anything explicit from the user except perhaps for a case
-      // where the header is generated out of nothing (so there is no need to
-      // explicitly mention its target in the buildfile). But this probably
-      // won't be very common.
+      // require anything explicit from the user.
       //
       // One tricky area in this setup are target groups: if the generated
       // sources are mentioned in the buildfile as a group, then there might
@@ -3546,10 +3055,7 @@ namespace build2
       // generated depending on the options (e.g., inline files might be
       // suppressed), headers are usually non-optional.
       //
-      // Note that we use path_map instead of dir_path_map to allow searching
-      // using path (file path).
-      //
-      srcout_map so_map; // path_map<dir_path>
+      srcout_map so_map;
 
       // Dynamic module mapper.
       //
@@ -3629,17 +3135,13 @@ namespace build2
           // Populate the src-out with the -I$out_base -I$src_base pairs.
           //
           {
+            srcout_builder builder (ctx, so_map);
+
             // Try to be fast and efficient by reusing buffers as much as
             // possible.
             //
             string ds;
 
-            // Previous -I innermost scope if out_base plus the difference
-            // between the scope path and the -I path (normally empty).
-            //
-            const scope* s (nullptr);
-            dir_path p;
-
             for (auto i (args.begin ()), e (args.end ()); i != e; ++i)
             {
               const char* o (*i);
@@ -3664,7 +3166,7 @@ namespace build2
 
                 if (p == 0)
                 {
-                  s = nullptr;
+                  builder.skip ();
                   continue;
                 }
 
@@ -3697,68 +3199,14 @@ namespace build2
                 //
                 if (!d.empty ())
                 {
-                  // Ignore any paths containing '.', '..' components. Allow
-                  // any directory separators though (think -I$src_root/foo
-                  // on Windows).
-                  //
-                  if (d.absolute () && d.normalized (false))
-                  {
-                    // If we have a candidate out_base, see if this is its
-                    // src_base.
-                    //
-                    if (s != nullptr)
-                    {
-                      const dir_path& bp (s->src_path ());
-
-                      if (d.sub (bp))
-                      {
-                        if (p.empty () || d.leaf (bp) == p)
-                        {
-                          // We've got a pair.
-                          //
-                          so_map.emplace (move (d), s->out_path () / p);
-                          s = nullptr; // Taken.
-                          continue;
-                        }
-                      }
-
-                      // Not a pair. Fall through to consider as out_base.
-                      //
-                      s = nullptr;
-                    }
-
-                    // See if this path is inside a project with an out-of-
-                    // tree build and is in the out directory tree.
-                    //
-                    const scope& bs (ctx.scopes.find_out (d));
-                    if (bs.root_scope () != nullptr)
-                    {
-                      if (!bs.out_eq_src ())
-                      {
-                        const dir_path& bp (bs.out_path ());
-
-                        bool e;
-                        if ((e = (d == bp)) || d.sub (bp))
-                        {
-                          s = &bs;
-                          if (e)
-                            p.clear ();
-                          else
-                            p = d.leaf (bp);
-                        }
-                      }
-                    }
-                  }
-                  else
-                    s = nullptr;
-
-                  ds = move (d).string (); // Move the buffer out.
+                  if (!builder.next (move (d)))
+                    ds = move (d).string (); // Move the buffer back out.
                 }
                 else
-                  s = nullptr;
+                  builder.skip ();
               }
               else
-                s = nullptr;
+                builder.skip ();
             }
           }
 
@@ -4098,15 +3546,12 @@ namespace build2
         // to be inconvenient: some users like to re-run a failed build with
         // -s not to get "swamped" with errors.
         //
-        bool df (!ctx.match_only && !ctx.dry_run_option);
-
-        const file* ht (enter_header (a, bs, t, li,
-                                      move (hp), cache, false /* norm */,
-                                      pfx_map, so_map).first);
-        if (ht == nullptr)
+        auto fail = [&ctx] (const auto& h) -> optional<bool>
         {
+          bool df (!ctx.match_only && !ctx.dry_run_option);
+
           diag_record dr;
-          dr << error << "header '" << hp << "' not found and no rule to "
+          dr << error << "header " << h << " not found and no rule to "
              << "generate it";
 
           if (df)
@@ -4115,41 +3560,42 @@ namespace build2
           if (verb < 4)
             dr << info << "re-run with --verbose=4 for more information";
 
-          if (df) return nullopt; else dr << endf;
-        }
+          if (df)
+            return nullopt;
+          else
+            dr << endf;
+        };
 
-        // If we are reading the cache, then it is possible the file has since
-        // been removed (think of a header in /usr/local/include that has been
-        // uninstalled and now we need to use one from /usr/include). This
-        // will lead to the match failure which we translate to a restart.
-        //
-        if (optional<bool> u = inject_header (a, t, *ht, mt, false /* fail */))
+        if (const file* ht = enter_header (a, bs, t, li,
+                                           move (hp), cache, false /* norm */,
+                                           pfx_map, so_map).first)
         {
-          // Verify/add it to the dependency database.
+          // If we are reading the cache, then it is possible the file has
+          // since been removed (think of a header in /usr/local/include that
+          // has been uninstalled and now we need to use one from
+          // /usr/include). This will lead to the match failure which we
+          // translate to a restart.
           //
-          if (!cache)
-            dd.expect (ht->path ());
-
-          skip_count++;
-          return *u;
-        }
-        else if (!cache)
-        {
-          diag_record dr;
-          dr << error << "header " << *ht << " not found and no rule to "
-             << "generate it";
-
-          if (df)
-            dr << info << "failure deferred to compiler diagnostics";
-
-          if (verb < 4)
-            dr << info << "re-run with --verbose=4 for more information";
+          if (optional<bool> u = inject_header (a, t, *ht, mt, false /*fail*/))
+          {
+            // Verify/add it to the dependency database.
+            //
+            if (!cache)
+              dd.expect (ht->path ());
 
-          if (df) return nullopt; else dr << endf;
+            skip_count++;
+            return *u;
+          }
+          else if (cache)
+          {
+            dd.write (); // Invalidate this line.
+            return true;
+          }
+          else
+            return fail (*ht);
         }
-
-        dd.write (); // Invalidate this line.
-        return true;
+        else
+          return fail (hp);
       };
 
       // As above but for a header unit. Note that currently it is only used
@@ -4172,7 +3618,7 @@ namespace build2
         if (ht == nullptr)
         {
           diag_record dr;
-          dr << error << "header '" << hp << "' not found and no rule to "
+          dr << error << "header " << hp << " not found and no rule to "
              << "generate it";
 
           if (df)
@@ -4218,6 +3664,16 @@ namespace build2
 
       const path* drmp (nullptr); // Points to drm.path () if active.
 
+      // If things go wrong (and they often do in this area), give the user a
+      // bit extra context.
+      //
+      auto df = make_diag_frame (
+        [&src](const diag_record& dr)
+        {
+          if (verb != 0)
+            dr << info << "while extracting header dependencies from " << src;
+        });
+
       // If nothing so far has invalidated the dependency database, then try
       // the cached data before running the compiler.
       //
@@ -4782,13 +4238,16 @@ namespace build2
 
                       if (second)
                       {
+                        // Skip the source file.
+                        //
+                        make_parser::next (l, pos, true /* prereq */);
                         second = false;
-                        next_make (l, pos); // Skip the source file.
                       }
 
                       while (pos != l.size ())
                       {
-                        string f (next_make (l, pos));
+                        string f (
+                          make_parser::next (l, pos, true /* prereq */).first);
 
                         // Skip until where we left off.
                         //
diff --git a/libbuild2/cc/compile-rule.hxx b/libbuild2/cc/compile-rule.hxx
index a211590..568c04b 100644
--- a/libbuild2/cc/compile-rule.hxx
+++ b/libbuild2/cc/compile-rule.hxx
@@ -8,7 +8,7 @@
 #include <libbuild2/utility.hxx>
 
 #include <libbuild2/rule.hxx>
-#include <libbuild2/dynamic.hxx>
+#include <libbuild2/dyndep.hxx>
 #include <libbuild2/file-cache.hxx>
 
 #include <libbuild2/cc/types.hxx>
@@ -93,45 +93,21 @@ namespace build2
                               const scope&,
                               action, const target&, linfo) const;
 
-      // Mapping of include prefixes (e.g., foo in <foo/bar>) for auto-
-      // generated headers to directories where they will be generated.
-      //
-      // We are using a prefix map of directories (dir_path_map) instead of
-      // just a map in order to also cover sub-paths (e.g., <foo/more/bar> if
-      // we continue with the example). Specifically, we need to make sure we
-      // don't treat foobar as a sub-directory of foo.
-      //
-      // The priority is used to decide who should override whom. Lesser
-      // values are considered higher priority. Note that we can have multiple
-      // prefixless mapping (where priority is used to determine the order).
-      // See append_prefixes() for details.
-      //
-      // @@ The keys should be normalized.
-      //
-      struct prefix_value
-      {
-        dir_path directory;
-        size_t priority;
-      };
-      using prefix_map = dir_path_multimap<prefix_value>;
+      using prefix_map = dyndep_rule::prefix_map;
+      using srcout_map = dyndep_rule::srcout_map;
 
       void
-      append_prefixes (prefix_map&, const target&, const variable&) const;
+      append_prefixes (prefix_map&,
+                       const scope&, const target&,
+                       const variable&) const;
 
       void
       append_library_prefixes (appended_libraries&, prefix_map&,
                                const scope&,
-                               action, target&, linfo) const;
+                               action, const target&, linfo) const;
 
       prefix_map
-      build_prefix_map (const scope&, action, target&, linfo) const;
-
-      small_vector<const target_type*, 2>
-      map_extension (const scope&, const string&, const string&) const;
-
-      // Src-to-out re-mapping. See extract_headers() for details.
-      //
-      using srcout_map = path_map<dir_path>;
+      build_prefix_map (const scope&, action, const target&, linfo) const;
 
       struct module_mapper_state;
 
@@ -145,7 +121,7 @@ namespace build2
       pair<const file*, bool>
       enter_header (action, const scope&, file&, linfo,
                     path&&, bool, bool,
-                    optional<prefix_map>&, srcout_map&) const;
+                    optional<prefix_map>&, const srcout_map&) const;
 
       optional<bool>
       inject_header (action, file&, const file&, timestamp, bool) const;
diff --git a/libbuild2/cc/utility.cxx b/libbuild2/cc/utility.cxx
index ffe3e03..e02f85a 100644
--- a/libbuild2/cc/utility.cxx
+++ b/libbuild2/cc/utility.cxx
@@ -3,10 +3,6 @@
 
 #include <libbuild2/cc/utility.hxx>
 
-#include <libbuild2/file.hxx>
-
-using namespace std;
-
 namespace build2
 {
   namespace cc
@@ -17,58 +13,5 @@ namespace build2
     const dir_path module_build_dir (dir_path (module_dir) /= "build");
     const dir_path module_build_modules_dir (
       dir_path (module_build_dir) /= "modules");
-
-    void
-    normalize_header (path& f)
-    {
-      // Interestingly, on most paltforms and with most compilers (Clang on
-      // Linux being a notable exception) most system/compiler headers are
-      // already normalized.
-      //
-      path_abnormality a (f.abnormalities ());
-      if (a != path_abnormality::none)
-      {
-        // While we can reasonably expect this path to exit, things do go
-        // south from time to time (like compiling under wine with file
-        // wlantypes.h included as WlanTypes.h).
-        //
-        try
-        {
-          // If we have any parent components, then we have to verify the
-          // normalized path matches realized.
-          //
-          path r;
-          if ((a & path_abnormality::parent) == path_abnormality::parent)
-          {
-            r = f;
-            r.realize ();
-          }
-
-          try
-          {
-            f.normalize ();
-
-            // Note that we might still need to resolve symlinks in the
-            // normalized path.
-            //
-            if (!r.empty () && f != r && path (f).realize () != r)
-              f = move (r);
-          }
-          catch (const invalid_path&)
-          {
-            assert (!r.empty ()); // Shouldn't have failed if no `..`.
-            f = move (r);         // Fallback to realize.
-          }
-        }
-        catch (const invalid_path&)
-        {
-          fail << "invalid header path '" << f.string () << "'";
-        }
-        catch (const system_error& e)
-        {
-          fail << "invalid header path '" << f.string () << "': " << e;
-        }
-      }
-    }
   }
 }
diff --git a/libbuild2/cc/utility.hxx b/libbuild2/cc/utility.hxx
index 42e53e3..6ba4a20 100644
--- a/libbuild2/cc/utility.hxx
+++ b/libbuild2/cc/utility.hxx
@@ -9,6 +9,7 @@
 #include <libbuild2/utility.hxx>
 
 #include <libbuild2/target.hxx>
+#include <libbuild2/filesystem.hxx>
 
 #include <libbuild2/bin/target.hxx>
 #include <libbuild2/bin/utility.hxx>
@@ -51,29 +52,11 @@ namespace build2
 
     // Normalize an absolute path to an existing header.
     //
-    // We used to just normalize the path but that could result in an invalid
-    // path (e.g., for some system/compiler headers on CentOS 7 with Clang
-    // 3.4) because of the symlinks (if a directory component is a symlink,
-    // then any following `..` are resolved relative to the target; see
-    // path::normalize() for background).
-    //
-    // Initially, to fix this, we realized (i.e., realpath(3)) it instead.
-    // But that turned out also not to be quite right since now we have all
-    // the symlinks resolved: conceptually it feels correct to keep the
-    // original header names since that's how the user chose to arrange things
-    // and practically this is how the compilers see/report them (e.g., the
-    // GCC module mapper).
-    //
-    // So now we have a pretty elaborate scheme where we try to use the
-    // normalized path if possible and fallback to realized. Normalized paths
-    // will work for situations where `..` does not cross symlink boundaries,
-    // which is the sane case. And for the insane case we only really care
-    // about out-of-project files (i.e., system/compiler headers). In other
-    // words, if you have the insane case inside your project, then you are on
-    // your own.
-    //
-    void
-    normalize_header (path&);
+    inline void
+    normalize_header (path& f)
+    {
+      normalize_external (f, "header");
+    }
   }
 }
 
diff --git a/libbuild2/dynamic.cxx b/libbuild2/dynamic.cxx
deleted file mode 100644
index 6dd439b..0000000
--- a/libbuild2/dynamic.cxx
+++ /dev/null
@@ -1,76 +0,0 @@
-// file      : libbuild2/dynamic.cxx -*- C++ -*-
-// license   : MIT; see accompanying LICENSE file
-
-#include <libbuild2/dynamic.hxx>
-
-#include <libbuild2/scope.hxx>
-#include <libbuild2/target.hxx>
-#include <libbuild2/context.hxx>
-#include <libbuild2/algorithm.hxx>
-#include <libbuild2/diagnostics.hxx>
-
-using namespace std;
-using namespace butl;
-
-namespace build2
-{
-  bool
-  update_during_match (tracer& trace, action a, const target& t, timestamp ts)
-  {
-    // In particular, this function is used to make sure header dependencies
-    // are up to date.
-    //
-    // There would normally be a lot of headers for every source file (think
-    // all the system headers) and just calling execute_direct() on all of
-    // them can get expensive. At the same time, most of these headers are
-    // existing files that we will never be updating (again, system headers,
-    // for example) and the rule that will match them is the fallback
-    // file_rule. That rule has an optimization: it returns noop_recipe (which
-    // causes the target state to be automatically set to unchanged) if the
-    // file is known to be up to date. So we do the update "smartly".
-    //
-    const path_target* pt (t.is_a<path_target> ());
-
-    if (pt == nullptr)
-      ts = timestamp_unknown;
-
-    target_state os (t.matched_state (a));
-
-    if (os == target_state::unchanged)
-    {
-      if (ts == timestamp_unknown)
-        return false;
-      else
-      {
-        // We expect the timestamp to be known (i.e., existing file).
-        //
-        timestamp mt (pt->mtime ());
-        assert (mt != timestamp_unknown);
-        return mt > ts;
-      }
-    }
-    else
-    {
-      // We only want to return true if our call to execute() actually caused
-      // an update. In particular, the target could already have been in
-      // target_state::changed because of the dynamic dependency extraction
-      // run for some other target.
-      //
-      // @@ MT perf: so we are going to switch the phase and execute for
-      //    any generated header.
-      //
-      phase_switch ps (t.ctx, run_phase::execute);
-      target_state ns (execute_direct (a, t));
-
-      if (ns != os && ns != target_state::unchanged)
-      {
-        l6 ([&]{trace << "updated " << t
-                      << "; old state " << os
-                      << "; new state " << ns;});
-        return true;
-      }
-      else
-        return ts != timestamp_unknown ? pt->newer (ts, ns) : false;
-    }
-  }
-}
diff --git a/libbuild2/dynamic.hxx b/libbuild2/dynamic.hxx
deleted file mode 100644
index 395a839..0000000
--- a/libbuild2/dynamic.hxx
+++ /dev/null
@@ -1,33 +0,0 @@
-// file      : libbuild2/dynamic.hxx -*- C++ -*-
-// license   : MIT; see accompanying LICENSE file
-
-#ifndef LIBBUILD2_DYNAMIC_HXX
-#define LIBBUILD2_DYNAMIC_HXX
-
-#include <libbuild2/types.hxx>
-#include <libbuild2/forward.hxx>
-#include <libbuild2/utility.hxx>
-
-#include <libbuild2/action.hxx>
-#include <libbuild2/target.hxx>
-
-#include <libbuild2/export.hxx>
-
-// Additional functionality that is normally only useful for implementing
-// rules with dynamic dependencies.
-//
-namespace build2
-{
-  class LIBBUILD2_SYMEXPORT dyndep_rule
-  {
-  public:
-    // Update the target during the match phase. Return true if it has changed
-    // or if the passed timestamp is not timestamp_unknown and is older than
-    // the target.
-    //
-    static bool
-    update (tracer&, action, const target&, timestamp);
-  };
-}
-
-#endif // LIBBUILD2_DYNAMIC_HXX
diff --git a/libbuild2/dyndep.cxx b/libbuild2/dyndep.cxx
new file mode 100644
index 0000000..51fa7bc
--- /dev/null
+++ b/libbuild2/dyndep.cxx
@@ -0,0 +1,667 @@
+// file      : libbuild2/dyndep.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/dyndep.hxx>
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/context.hxx>
+#include <libbuild2/algorithm.hxx>
+#include <libbuild2/filesystem.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  bool dyndep_rule::
+  update (tracer& trace, action a, const target& t, timestamp ts)
+  {
+    // In particular, this function is used to make sure header dependencies
+    // are up to date.
+    //
+    // There would normally be a lot of headers for every source file (think
+    // all the system headers) and just calling execute_direct() on all of
+    // them can get expensive. At the same time, most of these headers are
+    // existing files that we will never be updating (again, system headers,
+    // for example) and the rule that will match them is the fallback
+    // file_rule. That rule has an optimization: it returns noop_recipe (which
+    // causes the target state to be automatically set to unchanged) if the
+    // file is known to be up to date. So we do the update "smartly".
+    //
+    const path_target* pt (t.is_a<path_target> ());
+
+    if (pt == nullptr)
+      ts = timestamp_unknown;
+
+    target_state os (t.matched_state (a));
+
+    if (os == target_state::unchanged)
+    {
+      if (ts == timestamp_unknown)
+        return false;
+      else
+      {
+        // We expect the timestamp to be known (i.e., existing file).
+        //
+        timestamp mt (pt->mtime ());
+        assert (mt != timestamp_unknown);
+        return mt > ts;
+      }
+    }
+    else
+    {
+      // We only want to return true if our call to execute() actually caused
+      // an update. In particular, the target could already have been in
+      // target_state::changed because of the dynamic dependency extraction
+      // run for some other target.
+      //
+      // @@ MT perf: so we are going to switch the phase and execute for
+      //    any generated header.
+      //
+      phase_switch ps (t.ctx, run_phase::execute);
+      target_state ns (execute_direct (a, t));
+
+      if (ns != os && ns != target_state::unchanged)
+      {
+        l6 ([&]{trace << "updated " << t
+                      << "; old state " << os
+                      << "; new state " << ns;});
+        return true;
+      }
+      else
+        return ts != timestamp_unknown ? pt->newer (ts, ns) : false;
+    }
+  }
+
+  optional<bool> dyndep_rule::
+  inject_file (tracer& trace, const char* what,
+               action a, target& t,
+               const file& pt,
+               timestamp mt,
+               bool f)
+  {
+    // Even if failing we still use try_match() in order to issue consistent
+    // (with other places) diagnostics (rather than the generic "not rule to
+    // update ...").
+    //
+    if (!try_match (a, pt).first)
+    {
+      if (!f)
+        return nullopt;
+
+      diag_record dr;
+      dr << fail << what << ' ' << pt << " not found and no rule to "
+         << "generate it";
+
+      if (verb < 4)
+        dr << info << "re-run with --verbose=4 for more information";
+    }
+
+    bool r (update (trace, a, pt, mt));
+
+    // Add to our prerequisite target list.
+    //
+    t.prerequisite_targets[a].push_back (&pt);
+
+    return r;
+  }
+
+  // Reverse-lookup target type(s) from file name/extension.
+  //
+  // If the list of base target types is specified, then only these types and
+  // those derived from them are considered. Otherwise, any file-based type is
+  // considered but not the file type itself.
+  //
+  small_vector<const target_type*, 2> dyndep_rule::
+  map_extension (const scope& bs,
+                 const string& n, const string& e,
+                 const target_type* const* tts)
+  {
+    // We will just have to try all of the possible ones, in the "most
+    // likely to match" order.
+    //
+    auto test = [&bs, &n, &e] (const target_type& tt) -> bool
+    {
+      if (tt.default_extension != nullptr)
+      {
+        // Call the extension derivation function. Here we know that it will
+        // only use the target type and name from the target key so we can
+        // pass bogus values for the rest.
+        //
+        target_key tk {&tt, nullptr, nullptr, &n, nullopt};
+
+        // This is like prerequisite search.
+        //
+        optional<string> de (tt.default_extension (tk, bs, nullptr, true));
+
+        return de && *de == e;
+      }
+
+      return false;
+    };
+
+    small_vector<const target_type*, 2> r;
+
+    if (tts != nullptr)
+    {
+      // @@ What if these types are not known by this project? Maybe this
+      //    should just be unified with the below loop? Need to make sure
+      //    we don't rely on the order in which they are returned.
+      //
+      for (const target_type* const* p (tts); *p != nullptr; ++p)
+        if (test (**p))
+          r.push_back (*p);
+    }
+
+    // Next try target types derived from any of the base types (or file if
+    // there are no base types).
+    //
+    const target_type_map& ttm (bs.root_scope ()->root_extra->target_types);
+
+    for (auto i (ttm.type_begin ()), e (ttm.type_end ()); i != e; ++i)
+    {
+      const target_type& dt (i->second);
+
+      if (tts != nullptr)
+      {
+        for (const target_type* const* p (tts); *p != nullptr; ++p)
+        {
+          const target_type& bt (**p);
+
+          if (dt.is_a (bt))
+          {
+            if (dt != bt && test (dt))
+              r.push_back (&dt);
+
+            break;
+          }
+        }
+      }
+      else
+      {
+        // Anything file-derived but not the file itself.
+        //
+        if (dt.is_a<file> () && dt != file::static_type && test (dt))
+          r.push_back (&dt);
+      }
+    }
+
+    return r;
+  }
+
+  void dyndep_rule::
+  append_prefix (tracer& trace, prefix_map& m, const target& t, dir_path d)
+  {
+    // If the target directory is a sub-directory of the include directory,
+    // then the prefix is the difference between the two. Otherwise, leave it
+    // empty.
+    //
+    // The idea here is to make this "canonical" setup work auto-magically
+    // (using C/C++ #include's as an example):
+    //
+    // 1. We include all headers with a prefix, e.g., <foo/bar>.
+    //
+    // 2. The library target is in the foo/ sub-directory, e.g., /tmp/foo/.
+    //
+    // 3. The poptions variable contains -I/tmp.
+    //
+    dir_path p (t.dir.sub (d) ? t.dir.leaf (d) : dir_path ());
+
+    // We use the target's directory as out_base but that doesn't work well
+    // for targets that are stashed in subdirectories. So as a heuristics we
+    // are going to also enter the outer directories of the original prefix.
+    // It is, however, possible, that another directory after this one will
+    // produce one of these outer prefixes as its original prefix in which
+    // case we should override it.
+    //
+    // So we are going to assign the original prefix priority value 0
+    // (highest) and then increment it for each outer prefix.
+    //
+    auto enter = [&trace, &m] (dir_path p, dir_path d, size_t prio)
+    {
+      auto j (m.lower_bound (p)), e (m.end ());
+
+      if (j != e && j->first != p)
+        j = e;
+
+      if (j == m.end ())
+      {
+        if (verb >= 4)
+          trace << "new mapping for prefix '" << p << "'\n"
+                << "  new mapping to      " << d << " priority " << prio;
+
+        m.emplace (move (p), prefix_value {move (d), prio});
+      }
+      else if (p.empty ())
+      {
+        // For prefixless we keep all the entries since for them we have an
+        // extra check (target must be explicitly spelled out in a buildfile).
+        //
+        if (verb >= 4)
+          trace << "additional mapping for prefix '" << p << "'\n"
+                << "  new mapping to      " << d << " priority " << prio;
+
+        // Find the position where to insert according to the priority.
+        // For equal priorities we use the insertion order.
+        //
+        do
+        {
+          if (j->second.priority > prio)
+            break;
+        }
+        while (++j != e && j->first == p);
+
+        m.emplace_hint (j, move (p), prefix_value {move (d), prio});
+      }
+      else
+      {
+        prefix_value& v (j->second);
+
+        // We used to reject duplicates but it seems this can be reasonably
+        // expected to work according to the order of, say, -I options.
+        //
+        // Seeing that we normally have more "specific" -I paths first, (so
+        // that we don't pick up installed headers, etc), we ignore it.
+        //
+        if (v.directory == d)
+        {
+          if (v.priority > prio)
+            v.priority = prio;
+        }
+        else if (v.priority <= prio)
+        {
+          if (verb >= 4)
+            trace << "ignoring mapping for prefix '" << p << "'\n"
+                  << "  existing mapping to " << v.directory
+                  << " priority " << v.priority << '\n'
+                  << "  another mapping to  " << d << " priority " << prio;
+        }
+        else
+        {
+          if (verb >= 4)
+            trace << "overriding mapping for prefix '" << p << "'\n"
+                  << "  existing mapping to " << v.directory
+                  << " priority " << v.priority << '\n'
+                  << "  new mapping to      " << d << " priority " << prio;
+
+          v.directory = move (d);
+          v.priority = prio;
+        }
+      }
+    };
+
+    // Enter all outer prefixes, including prefixless.
+    //
+    // The prefixless part is fuzzy but seems to be doing the right thing
+    // ignoring/overriding-wise, at least in cases where one of the competing
+    // include search paths is a subdirectory of another.
+    //
+    for (size_t prio (0);; ++prio)
+    {
+      bool e (p.empty ());
+      enter ((e ? move (p) : p), (e ? move (d) : d), prio);
+      if (e)
+        break;
+      p = p.directory ();
+    }
+  }
+
+  bool dyndep_rule::srcout_builder::
+  next (dir_path&& d)
+  {
+    // Ignore any paths containing '.', '..' components. Allow any directory
+    // separators though (think -I$src_root/foo on Windows).
+    //
+    if (d.absolute () && d.normalized (false))
+    {
+      // If we have a candidate out_base, see if this is its src_base.
+      //
+      if (prev_ != nullptr)
+      {
+        const dir_path& bp (prev_->src_path ());
+
+        if (d.sub (bp))
+        {
+          if (diff_.empty () || d.leaf (bp) == diff_)
+          {
+            // We've got a pair.
+            //
+            map_.emplace (move (d), prev_->out_path () / diff_);
+            prev_ = nullptr; // Taken.
+            return true;
+          }
+        }
+
+        // Not a pair. Fall through to consider as out_base.
+        //
+        prev_ = nullptr;
+      }
+
+      // See if this path is inside a project with an out-of-tree build and is
+      // in the out directory tree.
+      //
+      const scope& bs (ctx_.scopes.find_out (d));
+      if (bs.root_scope () != nullptr)
+      {
+        if (!bs.out_eq_src ())
+        {
+          const dir_path& bp (bs.out_path ());
+
+          bool e;
+          if ((e = (d == bp)) || d.sub (bp))
+          {
+            prev_ = &bs;
+            if (e)
+              diff_.clear ();
+            else
+              diff_ = d.leaf (bp);
+          }
+        }
+      }
+    }
+    else
+      prev_ = nullptr;
+
+    return false;
+  }
+
+  pair<const file*, bool> dyndep_rule::
+  enter_file (tracer& trace, const char* what,
+              action a, const scope& bs, target& t,
+              path&& f, bool cache, bool norm,
+              const function<map_extension_func>& map_extension,
+              const target_type& fallback,
+              const function<prefix_map_func>& get_pfx_map,
+              const srcout_map& so_map)
+  {
+    // Find or maybe insert the target. The directory is only moved from if
+    // insert is true. Note that it must be normalized.
+    //
+    auto find = [&trace, what, &t,
+                 &map_extension, &fallback] (dir_path&& d,
+                                             path&& f,
+                                             bool insert) -> const file*
+    {
+      // Split the file into its name part and extension. Here we can assume
+      // the name part is a valid filesystem name.
+      //
+      // Note that if the file has no extension, we record an empty extension
+      // rather than NULL (which would signify that the default extension
+      // should be added).
+      //
+      string e (f.extension ());
+      string n (move (f).string ());
+
+      if (!e.empty ())
+        n.resize (n.size () - e.size () - 1); // One for the dot.
+
+      // See if this directory is part of any project and if so determine
+      // the target type.
+      //
+      // While at it also determine if this target is from the src or out
+      // tree of said project.
+      //
+      dir_path out;
+
+      // It's possible the extension-to-target type mapping is ambiguous (for
+      // example, because both C and X-language headers use the same .h
+      // extension). In this case we will first try to find one that matches
+      // an explicit target (similar logic to when insert is false).
+      //
+      small_vector<const target_type*, 2> tts;
+
+      // Note that the path can be in out or src directory and the latter
+      // can be associated with multiple scopes. So strictly speaking we
+      // need to pick one that is "associated" with us. But that is still a
+      // TODO (see scope_map::find() for details) and so for now we just
+      // pick the first one (it's highly unlikely the source file extension
+      // mapping will differ based on the configuration).
+      //
+      {
+        const scope& bs (**t.ctx.scopes.find (d).first);
+        if (const scope* rs = bs.root_scope ())
+        {
+          if (map_extension != nullptr)
+            tts = map_extension (bs, n, e);
+
+          if (!bs.out_eq_src () && d.sub (bs.src_path ()))
+            out = out_src (d, *rs);
+        }
+      }
+
+      // If it is outside any project, or the project doesn't have such an
+      // extension, use the fallback target type.
+      //
+      if (tts.empty ())
+      {
+        // If the project doesn't "know" this extension then we can't possibly
+        // find an explicit target of this type.
+        //
+        if (!insert)
+        {
+          l6 ([&]{trace << "unknown " << what << ' ' << n << " extension '"
+                        << e << "'";});
+          return nullptr;
+        }
+
+        tts.push_back (&fallback);
+      }
+
+      // Find or insert target.
+      //
+      // Note that in case of the target type ambiguity we first try to find
+      // an explicit target that resolves this ambiguity.
+      //
+      const target* r (nullptr);
+
+      if (!insert || tts.size () > 1)
+      {
+        // Note that we skip any target type-specific searches (like for an
+        // existing file) and go straight for the target object since we
+        // need to find the target explicitly spelled out.
+        //
+        // Also, it doesn't feel like we should be able to resolve an
+        // absolute path with a spelled-out extension to multiple targets.
+        //
+        for (const target_type* tt: tts)
+        {
+          if ((r = t.ctx.targets.find (*tt, d, out, n, e, trace)) != nullptr)
+            break;
+          else
+            l6 ([&]{trace << "no targe with target type " << tt->name;});
+        }
+
+        // Note: we can't do this because of the in-source builds where there
+        // won't be explicit targets for non-generated files.
+        //
+        // This should be harmless, however, since in our world generated file
+        // are spelled-out as explicit targets. And if not, we will still get
+        // an error, just a bit less specific.
+        //
+#if 0
+        if (r == nullptr && insert)
+        {
+          f = d / n;
+          if (!e.empty ())
+          {
+            f += '.';
+            f += e;
+          }
+
+          diag_record dr (fail);
+          dr << "ambiguous mapping of " << what ' ' << f << " to target type";
+          for (const target_type* tt: tts)
+            dr << info << "could be " << tt->name << "{}";
+          dr << info << "spell-out its target to resolve this ambiguity";
+        }
+#endif
+      }
+
+      // @@ OPT: move d, out, n
+      //
+      if (r == nullptr && insert)
+        r = &search (t, *tts[0], d, out, n, &e, nullptr);
+
+      return static_cast<const file*> (r);
+    };
+
+    // If it's not absolute then it either does not (yet) exist or is a
+    // relative ""-include (see init_args() for details). Reduce the second
+    // case to absolute.
+    //
+    // Note: we now always use absolute path to the translation unit so this
+    // no longer applies. But let's keep it for posterity.
+    //
+#if 0
+    if (f.relative () && rels.relative ())
+    {
+      // If the relative source path has a directory component, make sure it
+      // matches since ""-include will always start with that (none of the
+      // compilers we support try to normalize this path). Failed that we may
+      // end up searching for a generated header in a random (working)
+      // directory.
+      //
+      const string& fs (f.string ());
+      const string& ss (rels.string ());
+
+      size_t p (path::traits::rfind_separator (ss));
+
+      if (p == string::npos || // No directory.
+          (fs.size () > p + 1 &&
+           path::traits::compare (fs.c_str (), p, ss.c_str (), p) == 0))
+      {
+        path t (work / f); // The rels path is relative to work.
+
+        if (exists (t))
+          f = move (t);
+      }
+    }
+#endif
+
+    const file* pt (nullptr);
+    bool remapped (false);
+
+    // If still relative then it does not exist.
+    //
+    if (f.relative ())
+    {
+      // This is probably as often an error as an auto-generated file, so
+      // trace at level 4.
+      //
+      l4 ([&]{trace << "non-existent " << what << " '" << f << "'";});
+
+      f.normalize ();
+
+      // The relative path might still contain '..' (e.g., ../foo.hxx;
+      // presumably ""-include'ed). We don't attempt to support auto-
+      // generated files with such inclusion styles.
+      //
+      if (get_pfx_map != nullptr && f.normalized ())
+      {
+        const prefix_map& pfx_map (get_pfx_map (a, bs, t));
+
+        // First try the whole file. Then just the directory.
+        //
+        // @@ Has to be a separate map since the prefix can be the same as
+        //    the file name.
+        //
+        // auto i (pfx_map->find (f));
+
+        // Find the most qualified prefix of which we are a sub-path.
+        //
+        if (!pfx_map.empty ())
+        {
+          dir_path d (f.directory ());
+          auto p (pfx_map.sup_range (d));
+
+          if (p.first != p.second)
+          {
+            // Note that we can only have multiple entries for the
+            // prefixless mapping.
+            //
+            dir_path pd; // Reuse.
+            for (auto i (p.first); i != p.second; ++i)
+            {
+              // Note: value in pfx_map is not necessarily canonical.
+              //
+              pd = i->second.directory;
+              pd.canonicalize ();
+
+              l4 ([&]{trace << "try prefix '" << d << "' mapped to " << pd;});
+
+              // If this is a prefixless mapping, then only use it if we can
+              // resolve it to an existing target (i.e., it is explicitly
+              // spelled out in a buildfile). @@ Hm, I wonder why, it's not
+              // like we can generate any file without an explicit target.
+              // Maybe for diagnostics (i.e., we will actually try to build
+              // something there instead of just saying no mapping).
+              //
+              pt = find (pd / d, f.leaf (), !i->first.empty ());
+              if (pt != nullptr)
+              {
+                f = pd / f;
+                l4 ([&]{trace << "mapped as auto-generated " << f;});
+                break;
+              }
+              else
+                l4 ([&]{trace << "no explicit target in " << pd;});
+            }
+          }
+          else
+            l4 ([&]{trace << "no prefix map entry for '" << d << "'";});
+        }
+        else
+          l4 ([&]{trace << "prefix map is empty";});
+      }
+    }
+    else
+    {
+      // Normalize the path unless it comes from the depdb, in which case
+      // we've already done that (normally). This is also where we handle
+      // src-out remap (again, not needed if cached).
+      //
+      if (!cache || norm)
+        normalize_external (f, what);
+
+      if (!cache)
+      {
+        if (!so_map.empty ())
+        {
+          // Find the most qualified prefix of which we are a sub-path.
+          //
+          auto i (so_map.find_sup (f));
+          if (i != so_map.end ())
+          {
+            // Ok, there is an out tree for this file. Remap to a path from
+            // the out tree and see if there is a target for it. Note that the
+            // value in so_map is not necessarily canonical.
+            //
+            dir_path d (i->second);
+            d /= f.leaf (i->first).directory ();
+            d.canonicalize ();
+
+            pt = find (move (d), f.leaf (), false); // d is not moved from.
+
+            if (pt != nullptr)
+            {
+              path p (d / f.leaf ());
+              l4 ([&]{trace << "remapping " << f << " to " << p;});
+              f = move (p);
+              remapped = true;
+            }
+          }
+        }
+      }
+
+      if (pt == nullptr)
+      {
+        l6 ([&]{trace << "entering " << f;});
+        pt = find (f.directory (), f.leaf (), true);
+      }
+    }
+
+    return make_pair (pt, remapped);
+  }
+}
diff --git a/libbuild2/dyndep.hxx b/libbuild2/dyndep.hxx
new file mode 100644
index 0000000..3ba0c09
--- /dev/null
+++ b/libbuild2/dyndep.hxx
@@ -0,0 +1,168 @@
+// file      : libbuild2/dyndep.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_DYNDEP_HXX
+#define LIBBUILD2_DYNDEP_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/forward.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/action.hxx>
+#include <libbuild2/target.hxx>
+
+#include <libbuild2/export.hxx>
+
+// Additional functionality that is normally only useful for implementing
+// rules with dynamic dependencies.
+//
+namespace build2
+{
+  class LIBBUILD2_SYMEXPORT dyndep_rule
+  {
+  public:
+    // Update the target during the match phase. Return true if it has changed
+    // or if the passed timestamp is not timestamp_unknown and is older than
+    // the target.
+    //
+    static bool
+    update (tracer&, action, const target&, timestamp);
+
+    // Update and add to the list of prerequisite targets a prerequisite file
+    // target.
+    //
+    // Return the indication of whether it has changed or, if the passed
+    // timestamp is not timestamp_unknown, is older than this timestamp. If
+    // the prerequisite target does not exists nor can be generated (no rule),
+    // then issue diagnostics and fail if the fail argument is true and return
+    // nullopt otherwise.
+    //
+    static optional<bool>
+    inject_file (tracer&, const char* what,
+                 action, target&,
+                 const file& prerequiste,
+                 timestamp,
+                 bool fail);
+
+    // Reverse-lookup target type(s) from file name/extension.
+    //
+    // If the list of base target types is specified, then only these types
+    // and those derived from them are considered. Otherwise, any file-based
+    // type is considered but not the file type itself.
+    //
+    static small_vector<const target_type*, 2>
+    map_extension (const scope& base,
+                   const string& name, const string& ext,
+                   const target_type* const* bases);
+
+    // Mapping of inclusion prefixes (e.g., foo in #include <foo/bar>) for
+    // auto-generated files to inclusion search paths (e.g. -I) where they
+    // will be generated.
+    //
+    // We are using a prefix map of directories (dir_path_map) instead of just
+    // a map in order to also cover sub-paths (e.g., #include <foo/more/bar>
+    // if we continue with the example). Specifically, we need to make sure we
+    // don't treat foobar as a sub-directory of foo.
+    //
+    // The priority is used to decide who should override whom. Lesser values
+    // are considered higher priority. Note that we allow multiple prefixless
+    // mapping (where priority is used to determine the order). For details,
+    // see append_prefix().
+    //
+    // Note that the keys should be normalized.
+    //
+    struct prefix_value
+    {
+      dir_path directory;
+      size_t priority;
+    };
+
+    using prefix_map = dir_path_multimap<prefix_value>;
+
+    // Add the specified absolute and normalized inclusion search path into
+    // the prefix map of the specified target.
+    //
+    static void
+    append_prefix (tracer&, prefix_map&, const target&, dir_path);
+
+    // Mapping of src inclusion search paths to the corresponding out paths
+    // for auto-generated files re-mapping. See cc::extract_headers() for
+    // background.
+    //
+    // Note that we use path_map instead of dir_path_map to allow searching
+    // using path (file path).
+    //
+    using srcout_map = path_map<dir_path>;
+
+    class LIBBUILD2_SYMEXPORT srcout_builder
+    {
+    public:
+      srcout_builder (context& ctx, srcout_map& map): ctx_ (ctx), map_ (map) {}
+
+      // Process next -I path. Return true if an entry was added to the map,
+      // in which case the passed path is moved from.
+      //
+      bool
+      next (dir_path&&);
+
+      // Skip the previously cached first half.
+      //
+      void
+      skip ()
+      {
+        prev_ = nullptr;
+      }
+
+    private:
+      context& ctx_;
+      srcout_map& map_;
+
+      // Previous -I's innermost scope if out_base plus the difference between
+      // the scope path and the -I path (normally empty).
+      //
+      const scope* prev_ = nullptr;
+      dir_path diff_;
+    };
+
+    // Enter a prerequisite file as a target. If the path is relative, then
+    // assume this a non-existent generated file.
+    //
+    // Depending on the cache flag, the path is assumed to either have come
+    // from the depdb cache or from the compiler run. In the former case
+    // assume the path is already normalized unless the normalize flag is
+    // true.
+    //
+    // Return the file target and an indication of whether it was remapped or
+    // NULL if the file does not exist and cannot be generated. In the latter
+    // case the passed file path is guaranteed to still be valid but might
+    // have been adjusted (e.g., normalized, etc).
+    //
+    // The map_extension function is used to reverse-map a file extension to
+    // the target type. The fallback target type is used if it's NULL or
+    // didn't return anything but only in situations where we are sure the
+    // file is (or should be there; see the implementation for details).
+    //
+    // The prefix map function is only called if this is a non-existent
+    // generated file (so it can be initialized lazily). If it's NULL, then
+    // generated files will not be supported. The srcout map is only consulted
+    // if cache is false (so its initialization can be delayed until the call
+    // with cache=false).
+    //
+    using map_extension_func = small_vector<const target_type*, 2> (
+      const scope& base, const string& name, const string& ext);
+
+    using prefix_map_func = const prefix_map& (
+      action, const scope& base, const target&);
+
+    static pair<const file*, bool>
+    enter_file (tracer&, const char* what,
+                action, const scope& base, target&,
+                path&& prerequisite, bool cache, bool norm,
+                const function<map_extension_func>&,
+                const target_type& fallback,
+                const function<prefix_map_func>&,
+                const srcout_map&);
+  };
+}
+
+#endif // LIBBUILD2_DYNDEP_HXX
diff --git a/libbuild2/filesystem.cxx b/libbuild2/filesystem.cxx
index fbe145c..2e3309d 100644
--- a/libbuild2/filesystem.cxx
+++ b/libbuild2/filesystem.cxx
@@ -323,4 +323,59 @@ namespace build2
       fail << "unable to set path " << p << " permissions: " << e;
     }
   }
+
+  void
+  normalize_external (path& f, const char* what)
+  {
+    // The main motivating case for this logic are C/C++ headers.
+    //
+    // Interestingly, on most paltforms and with most compilers (Clang on
+    // Linux being a notable exception) most system/compiler headers are
+    // already normalized.
+    //
+    path_abnormality a (f.abnormalities ());
+    if (a != path_abnormality::none)
+    {
+      // While we can reasonably expect this path to exit, things do go south
+      // from time to time (like compiling under wine with file wlantypes.h
+      // included as WlanTypes.h).
+      //
+      try
+      {
+        // If we have any parent components, then we have to verify the
+        // normalized path matches realized.
+        //
+        path r;
+        if ((a & path_abnormality::parent) == path_abnormality::parent)
+        {
+          r = f;
+          r.realize ();
+        }
+
+        try
+        {
+          f.normalize ();
+
+          // Note that we might still need to resolve symlinks in the
+          // normalized path.
+          //
+          if (!r.empty () && f != r && path (f).realize () != r)
+            f = move (r);
+        }
+        catch (const invalid_path&)
+        {
+          assert (!r.empty ()); // Shouldn't have failed if no `..`.
+          f = move (r);         // Fallback to realize.
+        }
+      }
+      catch (const invalid_path&)
+      {
+        fail << "invalid " << what << " path '" << f.string () << "'";
+      }
+      catch (const system_error& e)
+      {
+        fail << "invalid " << what << " path '" << f.string () << "': " << e;
+      }
+    }
+  }
 }
diff --git a/libbuild2/filesystem.hxx b/libbuild2/filesystem.hxx
index ee7ba9a..565e832 100644
--- a/libbuild2/filesystem.hxx
+++ b/libbuild2/filesystem.hxx
@@ -189,6 +189,35 @@ namespace build2
 
   LIBBUILD2_SYMEXPORT void
   path_perms (const path&, permissions);
+
+  // Normalize an absolute path to an existing file that may reside outside of
+  // any project and could involve funny filesystem business (e.g., relative
+  // directory symlinks). For example, a C/C++ header path returned by a
+  // compiler which could be a system header.
+  //
+  // We used to just normalize such a path but that could result in an invalid
+  // path (e.g., for some system/compiler headers on CentOS 7 with Clang 3.4)
+  // because of the symlinks (if a directory component is a symlink, then any
+  // following `..` are resolved relative to the target; see path::normalize()
+  // for background).
+  //
+  // Initially, to fix this, we realized (i.e., realpath(3)) it instead. But
+  // that turned out also not to be quite right since now we have all the
+  // symlinks resolved: conceptually it feels correct to keep the original
+  // header names since that's how the user chose to arrange things and
+  // practically this is how compilers see/report them (e.g., the GCC module
+  // mapper).
+  //
+  // So now we have a pretty elaborate scheme where we try to use the
+  // normalized path if possible and fallback to realized. Normalized paths
+  // will work for situations where `..` does not cross symlink boundaries,
+  // which is the sane case. And for the insane case we only really care
+  // about out-of-project files (i.e., system/compiler headers). In other
+  // words, if you have the insane case inside your project, then you are on
+  // your own.
+  //
+  LIBBUILD2_SYMEXPORT void
+  normalize_external (path&, const char* what);
 }
 
 #include <libbuild2/filesystem.ixx>
diff --git a/libbuild2/make-parser.cxx b/libbuild2/make-parser.cxx
new file mode 100644
index 0000000..d076a0a
--- /dev/null
+++ b/libbuild2/make-parser.cxx
@@ -0,0 +1,137 @@
+// file      : libbuild2/make-parser.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/make-parser.hxx>
+
+#include <libbuild2/diagnostics.hxx>
+
+namespace build2
+{
+  auto make_parser::
+  next (const string& l,
+        size_t& p,
+        const location& ll,
+        bool strict) -> pair<type, string>
+  {
+    assert (state != end);
+
+    pair<string, bool> r (
+      next (l, p, !strict ? state == prereqs : optional<bool> ()));
+
+    type t (state == prereqs ? type::prereq : type::target);
+
+    // Deal with the end.
+    //
+    if (r.second)
+    {
+      if (state == begin && r.first.empty ())
+        ; // Skip leading blank line.
+      else
+      {
+        if (state != prereqs)
+          fail (ll) << "end of make dependency declaration before ':'";
+
+        state = end;
+      }
+    }
+    // Deal with the first target.
+    //
+    else if (state == begin && !r.first.empty ())
+      state = targets;
+
+    // Deal with `:`.
+    //
+    if (p != l.size () && l[p] == ':')
+    {
+      switch (state)
+      {
+      case begin:   fail (ll) << "':' before make target";      break;
+      case targets: state = prereqs;                            break;
+      case prereqs: fail (ll) << "':' after make prerequisite"; break;
+      case end:                                                 break;
+      }
+
+      if (++p == l.size ())
+        state = end; // Not a mere optimization: the caller will get next line.
+    }
+
+    return pair<type, string> (t, move (r.first));
+  }
+
+  pair<string, bool> make_parser::
+  next (const string& l, size_t& p, optional<bool> prereq)
+  {
+    size_t n (l.size ());
+
+    // Skip leading spaces.
+    //
+    for (; p != n && l[p] == ' '; p++) ;
+
+    // Lines containing multiple targets/prerequisites are customarily 80
+    // characters max.
+    //
+    string r;
+    r.reserve (n - p);
+
+    // Scan the next target/prerequisite while watching out for escape
+    // sequences.
+    //
+    // @@ Can't we do better for the (common) case where nothing is escaped?
+    //
+    for (char c, q (prereq && *prereq ? '\0' : ':');
+         p != n && (c = l[p]) != ' ' && c != q; )
+    {
+      // If we have another character, then handle the escapes.
+      //
+      if (++p != n)
+      {
+        if (c == '\\')
+        {
+          // This may or may not be an escape sequence depending on whether
+          // what follows is "escapable".
+          //
+          switch (c = l[p])
+          {
+          case '\\':
+          case ' ':
+          case ':': ++p; break;
+          default: c = '\\'; // Restore.
+          }
+        }
+        else if (c == '$')
+        {
+          // Got to be another (escaped) '$'.
+          //
+          if (l[p] == '$')
+            ++p;
+        }
+      }
+      // Note that the newline escape is not necessarily separated with space.
+      //
+      else if (c == '\\')
+      {
+        --p;
+        break;
+      }
+
+      r += c;
+    }
+
+    // Skip trailing spaces.
+    //
+    for (; p != n && l[p] == ' '; p++) ;
+
+    // Skip final '\' and determine if this is the end.
+    //
+    bool e (false);
+    if (p == n - 1)
+    {
+      if (l[p] == '\\')
+        p++;
+    }
+    else if (p == n)
+      e = true;
+
+    return pair<string, bool> (move (r), e);
+  }
+}
diff --git a/libbuild2/make-parser.hxx b/libbuild2/make-parser.hxx
new file mode 100644
index 0000000..fac2215
--- /dev/null
+++ b/libbuild2/make-parser.hxx
@@ -0,0 +1,85 @@
+// file      : libbuild2/make-parser.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_MAKE_PARSER_HXX
+#define LIBBUILD2_MAKE_PARSER_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/export.hxx>
+
+namespace build2
+{
+  // Make dependency declaration parser.
+  //
+  // The format is line-based (but with potential line continuations) so we
+  // parse one line at a time. This allows the caller to bail out early (for
+  // example, on encountering a non-existent generated file).
+  //
+  class LIBBUILD2_SYMEXPORT make_parser
+  {
+  public:
+    enum {begin, targets, prereqs, end} state = begin;
+
+    // Parse next target/prerequisite on a line starting from the specified
+    // position. Update the position to point to the start of the following
+    // target/prerequisite or l.size() if there is nothing left on this
+    // line. May return an empty string for a valid if unlikely dependency
+    // declarations (see below) or if passing leading blank lines (both of
+    // which should normally be just skipped). Issue diagnostics and throw
+    // failed if the declaration is invalid.
+    //
+    // If strict is false, then allow unescaped `:` in prerequisites.
+    //
+    // Note that the (p != l.size) should be in the do-while rather than in a
+    // while loop. In other words, except for the leading blank lines, the
+    // parser needs to see the blank line to correctly identify the end of the
+    // declaration. See make-parser.test.cxx for a recommended usage.
+    //
+    // To parse more than one declaration, reset the state to begin after
+    // reaching end.
+    //
+    enum class type {target, prereq};
+
+    pair<type, string>
+    next (const string&, size_t&, const location&, bool strict);
+
+    // Lower-level stateless API.
+    //
+  public:
+    // Parse next target/prerequisite on a line starting from the specified
+    // position. Return the target/prerequisite as well as an indication of
+    // whether the end of the dependency declaration was reached. Update the
+    // position to point to the start of the following target/prerequisite,
+    // `:`, or l.size() if there is nothing left on this line.
+    //
+    // Note that some broken tools (notably MinGW GCC) do not escape `:`
+    // properly. To tolerate such cases the caller may specify that what's
+    // being parsed is the prerequisite list in which case unescaped `:` will
+    // be treated literally.
+    //
+    // Note also that this function may return an empty string (with
+    // end=false) for a valid if unlikely dependency declaration, for example
+    // (using | to represent backslash):
+    //
+    // foo:|
+    // |
+    // bar
+    //
+    // It would also return an empty string (with end=true) if passed and
+    // empty or whitespace-only line.
+    //
+    // Note also that in the make language line continuations introduce a
+    // whitespace rather than just being remove. For example, the following
+    // declaration has two prerequisites:
+    //
+    // foo: bar|
+    // baz
+    //
+    static pair<string, bool>
+    next (const string&, size_t&, optional<bool> prereq = nullopt);
+  };
+}
+
+#endif // LIBBUILD2_MAKE_PARSER_HXX
diff --git a/libbuild2/make-parser.test.cxx b/libbuild2/make-parser.test.cxx
new file mode 100644
index 0000000..189407a
--- /dev/null
+++ b/libbuild2/make-parser.test.cxx
@@ -0,0 +1,90 @@
+// file      : libbuild2/make-parser.test.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <iostream>
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/make-parser.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#undef NDEBUG
+#include <cassert>
+
+using namespace std;
+
+namespace build2
+{
+  int
+  main (int, char* argv[])
+  {
+    bool strict (false);
+
+    // Fake build system driver, default verbosity.
+    //
+    init_diag (1);
+    init (nullptr, argv[0]);
+
+    path_name in ("<stdin>");
+
+    try
+    {
+      cin.exceptions (istream::badbit);
+
+      using make_state = make_parser;
+      using make_type = make_parser::type;
+
+      make_parser make;
+
+      location ll (in, 1);
+      for (string l; !eof (getline (cin, l)); ++ll.line)
+      {
+        if (make.state == make_state::end)
+        {
+          cout << endl;
+          make.state = make_state::begin;
+        }
+
+        // Skip leading blank lines to reduce output noise.
+        //
+        if (make.state == make_state::begin && l.empty ())
+          continue;
+
+        size_t pos (0);
+        do
+        {
+          pair<make_type, string> r (make.next (l, pos, ll, strict));
+
+          cout << (r.first == make_type::target ? 'T' : 'P');
+
+          if (!r.second.empty ())
+            cout << ' ' << r.second;
+
+          cout << endl;
+        }
+        while (pos != l.size ());
+      }
+
+      if (make.state != make_state::end && make.state != make_state::begin)
+        fail (ll) << "incomplete make dependency declaration";
+    }
+    catch (const io_error& e)
+    {
+      cerr << "unable to read stdin: " << e << endl;
+      return 1;
+    }
+    catch (const failed&)
+    {
+      return 1;
+    }
+
+    return 0;
+  }
+}
+
+int
+main (int argc, char* argv[])
+{
+  return build2::main (argc, argv);
+}
diff --git a/libbuild2/make-parser.test.testscript b/libbuild2/make-parser.test.testscript
new file mode 100644
index 0000000..6db00eb
--- /dev/null
+++ b/libbuild2/make-parser.test.testscript
@@ -0,0 +1,98 @@
+# file      : libbuild2/make-parser.test.testscript
+# license   : MIT; see accompanying LICENSE file
+
+: valid
+:
+$* <<EOI >>EOO
+  foo:
+
+  foo: bar
+
+  foo: bar baz
+
+  foo: bar \
+  baz
+
+  foo: bar\
+  baz
+
+  foo:\
+  bar baz\
+  fox
+
+  foo: bar \
+  \
+  baz
+
+  foo: bar\
+
+  foo bar: baz
+
+  foo \
+  bar: baz
+
+  foo \
+  bar \
+  : baz
+
+  \
+  foo: bar
+  EOI
+  T foo
+
+  T foo
+  P bar
+
+  T foo
+  P bar
+  P baz
+
+  T foo
+  P bar
+  P baz
+
+  T foo
+  P bar
+  P baz
+
+  T foo
+  P
+  P bar
+  P baz
+  P fox
+
+  T foo
+  P bar
+  P
+  P baz
+
+  T foo
+  P bar
+  P
+
+  T foo
+  T bar
+  P baz
+
+  T foo
+  T bar
+  P baz
+
+  T foo
+  T bar
+  T
+  P baz
+
+  T
+  T foo
+  P bar
+  EOO
+
+: lax
+:
+$* <<EOI >>EOO
+  foo: c:\tmp\bar
+  EOI
+  T foo
+  P c:\tmp\bar
+  EOO