Add support for dynamic dependencies in ad hoc Buildscript recipes

Specifically, add the new `depdb dyndep` builtin that can be used to extract
dynamic dependencies from a program run or a file. For example:

obje{hello.o}: cxx{hello}
{{
  s = $path($<[0])

  depdb dyndep $cxx.poptions $cc.poptions --what=header --default-prereq-type=h -- $cxx.path $cxx.poptions $cc.poptions $cxx.mode -M -MG $s

  diag c++ ($<[0])

  o = $path($>)
  $cxx.path $cxx.poptions $cc.poptions $cc.coptions $cxx.coptions $cxx.mode -o $o -c $s
}}

Currently only the `make` dependency format is supported.

10 files changed, 2501 insertions, 94 deletions

diff --git a/libbuild2/build/script/builtin-options.cxx b/libbuild2/build/script/builtin-options.cxx
new file mode 100644
index 0000000..cf99b12
--- /dev/null
+++ b/libbuild2/build/script/builtin-options.cxx
@@ -0,0 +1,701 @@
+// -*- C++ -*-
+//
+// This file was generated by CLI, a command line interface
+// compiler for C++.
+//
+
+// Begin prologue.
+//
+#include <libbuild2/build/script/types-parsers.hxx>
+//
+// End prologue.
+
+#include <libbuild2/build/script/builtin-options.hxx>
+
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+#include <utility>
+#include <ostream>
+#include <sstream>
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      namespace cli
+      {
+        // unknown_option
+        //
+        unknown_option::
+        ~unknown_option () throw ()
+        {
+        }
+
+        void unknown_option::
+        print (::std::ostream& os) const
+        {
+          os << "unknown option '" << option ().c_str () << "'";
+        }
+
+        const char* unknown_option::
+        what () const throw ()
+        {
+          return "unknown option";
+        }
+
+        // unknown_argument
+        //
+        unknown_argument::
+        ~unknown_argument () throw ()
+        {
+        }
+
+        void unknown_argument::
+        print (::std::ostream& os) const
+        {
+          os << "unknown argument '" << argument ().c_str () << "'";
+        }
+
+        const char* unknown_argument::
+        what () const throw ()
+        {
+          return "unknown argument";
+        }
+
+        // missing_value
+        //
+        missing_value::
+        ~missing_value () throw ()
+        {
+        }
+
+        void missing_value::
+        print (::std::ostream& os) const
+        {
+          os << "missing value for option '" << option ().c_str () << "'";
+        }
+
+        const char* missing_value::
+        what () const throw ()
+        {
+          return "missing option value";
+        }
+
+        // invalid_value
+        //
+        invalid_value::
+        ~invalid_value () throw ()
+        {
+        }
+
+        void invalid_value::
+        print (::std::ostream& os) const
+        {
+          os << "invalid value '" << value ().c_str () << "' for option '"
+             << option ().c_str () << "'";
+
+          if (!message ().empty ())
+            os << ": " << message ().c_str ();
+        }
+
+        const char* invalid_value::
+        what () const throw ()
+        {
+          return "invalid option value";
+        }
+
+        // eos_reached
+        //
+        void eos_reached::
+        print (::std::ostream& os) const
+        {
+          os << what ();
+        }
+
+        const char* eos_reached::
+        what () const throw ()
+        {
+          return "end of argument stream reached";
+        }
+
+        // scanner
+        //
+        scanner::
+        ~scanner ()
+        {
+        }
+
+        // argv_scanner
+        //
+        bool argv_scanner::
+        more ()
+        {
+          return i_ < argc_;
+        }
+
+        const char* argv_scanner::
+        peek ()
+        {
+          if (i_ < argc_)
+            return argv_[i_];
+          else
+            throw eos_reached ();
+        }
+
+        const char* argv_scanner::
+        next ()
+        {
+          if (i_ < argc_)
+          {
+            const char* r (argv_[i_]);
+
+            if (erase_)
+            {
+              for (int i (i_ + 1); i < argc_; ++i)
+                argv_[i - 1] = argv_[i];
+
+              --argc_;
+              argv_[argc_] = 0;
+            }
+            else
+              ++i_;
+
+            ++start_position_;
+            return r;
+          }
+          else
+            throw eos_reached ();
+        }
+
+        void argv_scanner::
+        skip ()
+        {
+          if (i_ < argc_)
+          {
+            ++i_;
+            ++start_position_;
+          }
+          else
+            throw eos_reached ();
+        }
+
+        std::size_t argv_scanner::
+        position ()
+        {
+          return start_position_;
+        }
+
+        // vector_scanner
+        //
+        bool vector_scanner::
+        more ()
+        {
+          return i_ < v_.size ();
+        }
+
+        const char* vector_scanner::
+        peek ()
+        {
+          if (i_ < v_.size ())
+            return v_[i_].c_str ();
+          else
+            throw eos_reached ();
+        }
+
+        const char* vector_scanner::
+        next ()
+        {
+          if (i_ < v_.size ())
+            return v_[i_++].c_str ();
+          else
+            throw eos_reached ();
+        }
+
+        void vector_scanner::
+        skip ()
+        {
+          if (i_ < v_.size ())
+            ++i_;
+          else
+            throw eos_reached ();
+        }
+
+        std::size_t vector_scanner::
+        position ()
+        {
+          return start_position_ + i_;
+        }
+
+        template <typename X>
+        struct parser
+        {
+          static void
+          parse (X& x, bool& xs, scanner& s)
+          {
+            using namespace std;
+
+            const char* o (s.next ());
+            if (s.more ())
+            {
+              string v (s.next ());
+              istringstream is (v);
+              if (!(is >> x && is.peek () == istringstream::traits_type::eof ()))
+                throw invalid_value (o, v);
+            }
+            else
+              throw missing_value (o);
+
+            xs = true;
+          }
+        };
+
+        template <>
+        struct parser<bool>
+        {
+          static void
+          parse (bool& x, scanner& s)
+          {
+            s.next ();
+            x = true;
+          }
+        };
+
+        template <>
+        struct parser<std::string>
+        {
+          static void
+          parse (std::string& x, bool& xs, scanner& s)
+          {
+            const char* o (s.next ());
+
+            if (s.more ())
+              x = s.next ();
+            else
+              throw missing_value (o);
+
+            xs = true;
+          }
+        };
+
+        template <typename X>
+        struct parser<std::pair<X, std::size_t> >
+        {
+          static void
+          parse (std::pair<X, std::size_t>& x, bool& xs, scanner& s)
+          {
+            x.second = s.position ();
+            parser<X>::parse (x.first, xs, s);
+          }
+        };
+
+        template <typename X>
+        struct parser<std::vector<X> >
+        {
+          static void
+          parse (std::vector<X>& c, bool& xs, scanner& s)
+          {
+            X x;
+            bool dummy;
+            parser<X>::parse (x, dummy, s);
+            c.push_back (x);
+            xs = true;
+          }
+        };
+
+        template <typename X, typename C>
+        struct parser<std::set<X, C> >
+        {
+          static void
+          parse (std::set<X, C>& c, bool& xs, scanner& s)
+          {
+            X x;
+            bool dummy;
+            parser<X>::parse (x, dummy, s);
+            c.insert (x);
+            xs = true;
+          }
+        };
+
+        template <typename K, typename V, typename C>
+        struct parser<std::map<K, V, C> >
+        {
+          static void
+          parse (std::map<K, V, C>& m, bool& xs, scanner& s)
+          {
+            const char* o (s.next ());
+
+            if (s.more ())
+            {
+              std::size_t pos (s.position ());
+              std::string ov (s.next ());
+              std::string::size_type p = ov.find ('=');
+
+              K k = K ();
+              V v = V ();
+              std::string kstr (ov, 0, p);
+              std::string vstr (ov, (p != std::string::npos ? p + 1 : ov.size ()));
+
+              int ac (2);
+              char* av[] =
+              {
+                const_cast<char*> (o),
+                0
+              };
+
+              bool dummy;
+              if (!kstr.empty ())
+              {
+                av[1] = const_cast<char*> (kstr.c_str ());
+                argv_scanner s (0, ac, av, false, pos);
+                parser<K>::parse (k, dummy, s);
+              }
+
+              if (!vstr.empty ())
+              {
+                av[1] = const_cast<char*> (vstr.c_str ());
+                argv_scanner s (0, ac, av, false, pos);
+                parser<V>::parse (v, dummy, s);
+              }
+
+              m[k] = v;
+            }
+            else
+              throw missing_value (o);
+
+            xs = true;
+          }
+        };
+
+        template <typename X, typename T, T X::*M>
+        void
+        thunk (X& x, scanner& s)
+        {
+          parser<T>::parse (x.*M, s);
+        }
+
+        template <typename X, typename T, T X::*M, bool X::*S>
+        void
+        thunk (X& x, scanner& s)
+        {
+          parser<T>::parse (x.*M, x.*S, s);
+        }
+      }
+    }
+  }
+}
+
+#include <map>
+#include <cstring>
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      // depdb_dep_options
+      //
+
+      depdb_dep_options::
+      depdb_dep_options ()
+      : file_ (),
+        file_specified_ (false),
+        format_ (),
+        format_specified_ (false),
+        what_ (),
+        what_specified_ (false),
+        include_path_ (),
+        include_path_specified_ (false),
+        default_prereq_type_ (),
+        default_prereq_type_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);
+        bool r = _parse (s, opt, arg);
+        return r;
+      }
+
+      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);
+        bool r = _parse (s, opt, arg);
+        return r;
+      }
+
+      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);
+        bool r = _parse (s, opt, arg);
+        end = s.end ();
+        return r;
+      }
+
+      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);
+        bool r = _parse (s, opt, arg);
+        end = s.end ();
+        return r;
+      }
+
+      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)
+      {
+        bool r = _parse (s, opt, arg);
+        return r;
+      }
+
+      typedef
+      std::map<std::string, void (*) (depdb_dep_options&, ::build2::build::script::cli::scanner&)>
+      _cli_depdb_dep_options_map;
+
+      static _cli_depdb_dep_options_map _cli_depdb_dep_options_map_;
+
+      struct _cli_depdb_dep_options_map_init
+      {
+        _cli_depdb_dep_options_map_init ()
+        {
+          _cli_depdb_dep_options_map_["--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_ >;
+        }
+      };
+
+      static _cli_depdb_dep_options_map_init _cli_depdb_dep_options_map_init_;
+
+      bool depdb_dep_options::
+      _parse (const char* o, ::build2::build::script::cli::scanner& s)
+      {
+        _cli_depdb_dep_options_map::const_iterator i (_cli_depdb_dep_options_map_.find (o));
+
+        if (i != _cli_depdb_dep_options_map_.end ())
+        {
+          (*(i->second)) (*this, s);
+          return true;
+        }
+
+        return false;
+      }
+
+      bool depdb_dep_options::
+      _parse (::build2::build::script::cli::scanner& s,
+              ::build2::build::script::cli::unknown_mode opt_mode,
+              ::build2::build::script::cli::unknown_mode arg_mode)
+      {
+        // Can't skip combined flags (--no-combined-flags).
+        //
+        assert (opt_mode != ::build2::build::script::cli::unknown_mode::skip);
+
+        bool r = false;
+        bool opt = true;
+
+        while (s.more ())
+        {
+          const char* o = s.peek ();
+
+          if (std::strcmp (o, "--") == 0)
+          {
+            opt = false;
+            s.skip ();
+            r = true;
+            continue;
+          }
+
+          if (opt)
+          {
+            if (_parse (o, s))
+            {
+              r = true;
+              continue;
+            }
+
+            if (std::strncmp (o, "-", 1) == 0 && o[1] != '\0')
+            {
+              // Handle combined option values.
+              //
+              std::string co;
+              if (const char* v = std::strchr (o, '='))
+              {
+                co.assign (o, 0, v - o);
+                ++v;
+
+                int ac (2);
+                char* av[] =
+                {
+                  const_cast<char*> (co.c_str ()),
+                  const_cast<char*> (v)
+                };
+
+                ::build2::build::script::cli::argv_scanner ns (0, ac, av);
+
+                if (_parse (co.c_str (), ns))
+                {
+                  // Parsed the option but not its value?
+                  //
+                  if (ns.end () != 2)
+                    throw ::build2::build::script::cli::invalid_value (co, v);
+
+                  s.next ();
+                  r = true;
+                  continue;
+                }
+                else
+                {
+                  // Set the unknown option and fall through.
+                  //
+                  o = co.c_str ();
+                }
+              }
+
+              // Handle combined flags.
+              //
+              char cf[3];
+              {
+                const char* p = o + 1;
+                for (; *p != '\0'; ++p)
+                {
+                  if (!((*p >= 'a' && *p <= 'z') ||
+                        (*p >= 'A' && *p <= 'Z') ||
+                        (*p >= '0' && *p <= '9')))
+                    break;
+                }
+
+                if (*p == '\0')
+                {
+                  for (p = o + 1; *p != '\0'; ++p)
+                  {
+                    std::strcpy (cf, "-");
+                    cf[1] = *p;
+                    cf[2] = '\0';
+
+                    int ac (1);
+                    char* av[] =
+                    {
+                      cf
+                    };
+
+                    ::build2::build::script::cli::argv_scanner ns (0, ac, av);
+
+                    if (!_parse (cf, ns))
+                      break;
+                  }
+
+                  if (*p == '\0')
+                  {
+                    // All handled.
+                    //
+                    s.next ();
+                    r = true;
+                    continue;
+                  }
+                  else
+                  {
+                    // Set the unknown option and fall through.
+                    //
+                    o = cf;
+                  }
+                }
+              }
+
+              switch (opt_mode)
+              {
+                case ::build2::build::script::cli::unknown_mode::skip:
+                {
+                  s.skip ();
+                  r = true;
+                  continue;
+                }
+                case ::build2::build::script::cli::unknown_mode::stop:
+                {
+                  break;
+                }
+                case ::build2::build::script::cli::unknown_mode::fail:
+                {
+                  throw ::build2::build::script::cli::unknown_option (o);
+                }
+              }
+
+              break;
+            }
+          }
+
+          switch (arg_mode)
+          {
+            case ::build2::build::script::cli::unknown_mode::skip:
+            {
+              s.skip ();
+              r = true;
+              continue;
+            }
+            case ::build2::build::script::cli::unknown_mode::stop:
+            {
+              break;
+            }
+            case ::build2::build::script::cli::unknown_mode::fail:
+            {
+              throw ::build2::build::script::cli::unknown_argument (o);
+            }
+          }
+
+          break;
+        }
+
+        return r;
+      }
+    }
+  }
+}
+
+// Begin epilogue.
+//
+//
+// End epilogue.
+
diff --git a/libbuild2/build/script/builtin-options.hxx b/libbuild2/build/script/builtin-options.hxx
new file mode 100644
index 0000000..85d67b9
--- /dev/null
+++ b/libbuild2/build/script/builtin-options.hxx
@@ -0,0 +1,456 @@
+// -*- C++ -*-
+//
+// This file was generated by CLI, a command line interface
+// compiler for C++.
+//
+
+#ifndef LIBBUILD2_BUILD_SCRIPT_BUILTIN_OPTIONS_HXX
+#define LIBBUILD2_BUILD_SCRIPT_BUILTIN_OPTIONS_HXX
+
+// Begin prologue.
+//
+//
+// End prologue.
+
+#include <vector>
+#include <iosfwd>
+#include <string>
+#include <cstddef>
+#include <exception>
+
+#ifndef CLI_POTENTIALLY_UNUSED
+#  if defined(_MSC_VER) || defined(__xlC__)
+#    define CLI_POTENTIALLY_UNUSED(x) (void*)&x
+#  else
+#    define CLI_POTENTIALLY_UNUSED(x) (void)x
+#  endif
+#endif
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      namespace cli
+      {
+        class unknown_mode
+        {
+          public:
+          enum value
+          {
+            skip,
+            stop,
+            fail
+          };
+
+          unknown_mode (value);
+
+          operator value () const 
+          {
+            return v_;
+          }
+
+          private:
+          value v_;
+        };
+
+        // Exceptions.
+        //
+
+        class exception: public std::exception
+        {
+          public:
+          virtual void
+          print (::std::ostream&) const = 0;
+        };
+
+        ::std::ostream&
+        operator<< (::std::ostream&, const exception&);
+
+        class unknown_option: public exception
+        {
+          public:
+          virtual
+          ~unknown_option () throw ();
+
+          unknown_option (const std::string& option);
+
+          const std::string&
+          option () const;
+
+          virtual void
+          print (::std::ostream&) const;
+
+          virtual const char*
+          what () const throw ();
+
+          private:
+          std::string option_;
+        };
+
+        class unknown_argument: public exception
+        {
+          public:
+          virtual
+          ~unknown_argument () throw ();
+
+          unknown_argument (const std::string& argument);
+
+          const std::string&
+          argument () const;
+
+          virtual void
+          print (::std::ostream&) const;
+
+          virtual const char*
+          what () const throw ();
+
+          private:
+          std::string argument_;
+        };
+
+        class missing_value: public exception
+        {
+          public:
+          virtual
+          ~missing_value () throw ();
+
+          missing_value (const std::string& option);
+
+          const std::string&
+          option () const;
+
+          virtual void
+          print (::std::ostream&) const;
+
+          virtual const char*
+          what () const throw ();
+
+          private:
+          std::string option_;
+        };
+
+        class invalid_value: public exception
+        {
+          public:
+          virtual
+          ~invalid_value () throw ();
+
+          invalid_value (const std::string& option,
+                         const std::string& value,
+                         const std::string& message = std::string ());
+
+          const std::string&
+          option () const;
+
+          const std::string&
+          value () const;
+
+          const std::string&
+          message () const;
+
+          virtual void
+          print (::std::ostream&) const;
+
+          virtual const char*
+          what () const throw ();
+
+          private:
+          std::string option_;
+          std::string value_;
+          std::string message_;
+        };
+
+        class eos_reached: public exception
+        {
+          public:
+          virtual void
+          print (::std::ostream&) const;
+
+          virtual const char*
+          what () const throw ();
+        };
+
+        // Command line argument scanner interface.
+        //
+        // The values returned by next() are guaranteed to be valid
+        // for the two previous arguments up until a call to a third
+        // peek() or next().
+        //
+        // The position() function returns a monotonically-increasing
+        // number which, if stored, can later be used to determine the
+        // relative position of the argument returned by the following
+        // call to next(). Note that if multiple scanners are used to
+        // extract arguments from multiple sources, then the end
+        // position of the previous scanner should be used as the
+        // start position of the next.
+        //
+        class scanner
+        {
+          public:
+          virtual
+          ~scanner ();
+
+          virtual bool
+          more () = 0;
+
+          virtual const char*
+          peek () = 0;
+
+          virtual const char*
+          next () = 0;
+
+          virtual void
+          skip () = 0;
+
+          virtual std::size_t
+          position () = 0;
+        };
+
+        class argv_scanner: public scanner
+        {
+          public:
+          argv_scanner (int& argc,
+                        char** argv,
+                        bool erase = false,
+                        std::size_t start_position = 0);
+
+          argv_scanner (int start,
+                        int& argc,
+                        char** argv,
+                        bool erase = false,
+                        std::size_t start_position = 0);
+
+          int
+          end () const;
+
+          virtual bool
+          more ();
+
+          virtual const char*
+          peek ();
+
+          virtual const char*
+          next ();
+
+          virtual void
+          skip ();
+
+          virtual std::size_t
+          position ();
+
+          protected:
+          std::size_t start_position_;
+          int i_;
+          int& argc_;
+          char** argv_;
+          bool erase_;
+        };
+
+        class vector_scanner: public scanner
+        {
+          public:
+          vector_scanner (const std::vector<std::string>&,
+                          std::size_t start = 0,
+                          std::size_t start_position = 0);
+
+          std::size_t
+          end () const;
+
+          void
+          reset (std::size_t start = 0, std::size_t start_position = 0);
+
+          virtual bool
+          more ();
+
+          virtual const char*
+          peek ();
+
+          virtual const char*
+          next ();
+
+          virtual void
+          skip ();
+
+          virtual std::size_t
+          position ();
+
+          private:
+          std::size_t start_position_;
+          const std::vector<std::string>& v_;
+          std::size_t i_;
+        };
+
+        template <typename X>
+        struct parser;
+      }
+    }
+  }
+}
+
+#include <libbuild2/types.hxx>
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      class depdb_dep_options
+      {
+        public:
+        depdb_dep_options ();
+
+        // 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 path&
+        file () const;
+
+        path&
+        file ();
+
+        void
+        file (const path&);
+
+        bool
+        file_specified () const;
+
+        void
+        file_specified (bool);
+
+        const string&
+        format () const;
+
+        string&
+        format ();
+
+        void
+        format (const string&);
+
+        bool
+        format_specified () const;
+
+        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:
+        bool
+        _parse (const char*, ::build2::build::script::cli::scanner&);
+
+        private:
+        bool
+        _parse (::build2::build::script::cli::scanner&,
+                ::build2::build::script::cli::unknown_mode option,
+                ::build2::build::script::cli::unknown_mode argument);
+
+        public:
+        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_;
+      };
+    }
+  }
+}
+
+#include <libbuild2/build/script/builtin-options.ixx>
+
+// Begin epilogue.
+//
+//
+// End epilogue.
+
+#endif // LIBBUILD2_BUILD_SCRIPT_BUILTIN_OPTIONS_HXX
diff --git a/libbuild2/build/script/builtin-options.ixx b/libbuild2/build/script/builtin-options.ixx
new file mode 100644
index 0000000..06575c8
--- /dev/null
+++ b/libbuild2/build/script/builtin-options.ixx
@@ -0,0 +1,338 @@
+// -*- C++ -*-
+//
+// This file was generated by CLI, a command line interface
+// compiler for C++.
+//
+
+// Begin prologue.
+//
+//
+// End prologue.
+
+#include <cassert>
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      namespace cli
+      {
+        // unknown_mode
+        //
+        inline unknown_mode::
+        unknown_mode (value v)
+        : v_ (v)
+        {
+        }
+
+        // exception
+        //
+        inline ::std::ostream&
+        operator<< (::std::ostream& os, const exception& e)
+        {
+          e.print (os);
+          return os;
+        }
+
+        // unknown_option
+        //
+        inline unknown_option::
+        unknown_option (const std::string& option)
+        : option_ (option)
+        {
+        }
+
+        inline const std::string& unknown_option::
+        option () const
+        {
+          return option_;
+        }
+
+        // unknown_argument
+        //
+        inline unknown_argument::
+        unknown_argument (const std::string& argument)
+        : argument_ (argument)
+        {
+        }
+
+        inline const std::string& unknown_argument::
+        argument () const
+        {
+          return argument_;
+        }
+
+        // missing_value
+        //
+        inline missing_value::
+        missing_value (const std::string& option)
+        : option_ (option)
+        {
+        }
+
+        inline const std::string& missing_value::
+        option () const
+        {
+          return option_;
+        }
+
+        // invalid_value
+        //
+        inline invalid_value::
+        invalid_value (const std::string& option,
+                       const std::string& value,
+                       const std::string& message)
+        : option_ (option),
+          value_ (value),
+          message_ (message)
+        {
+        }
+
+        inline const std::string& invalid_value::
+        option () const
+        {
+          return option_;
+        }
+
+        inline const std::string& invalid_value::
+        value () const
+        {
+          return value_;
+        }
+
+        inline const std::string& invalid_value::
+        message () const
+        {
+          return message_;
+        }
+
+        // argv_scanner
+        //
+        inline argv_scanner::
+        argv_scanner (int& argc,
+                      char** argv,
+                      bool erase,
+                      std::size_t sp)
+        : start_position_ (sp + 1),
+          i_ (1),
+          argc_ (argc),
+          argv_ (argv),
+          erase_ (erase)
+        {
+        }
+
+        inline argv_scanner::
+        argv_scanner (int start,
+                      int& argc,
+                      char** argv,
+                      bool erase,
+                      std::size_t sp)
+        : start_position_ (sp + static_cast<std::size_t> (start)),
+          i_ (start),
+          argc_ (argc),
+          argv_ (argv),
+          erase_ (erase)
+        {
+        }
+
+        inline int argv_scanner::
+        end () const
+        {
+          return i_;
+        }
+
+        // vector_scanner
+        //
+        inline vector_scanner::
+        vector_scanner (const std::vector<std::string>& v,
+                        std::size_t i,
+                        std::size_t sp)
+        : start_position_ (sp), v_ (v), i_ (i)
+        {
+        }
+
+        inline std::size_t vector_scanner::
+        end () const
+        {
+          return i_;
+        }
+
+        inline void vector_scanner::
+        reset (std::size_t i, std::size_t sp)
+        {
+          i_ = i;
+          start_position_ = sp;
+        }
+      }
+    }
+  }
+}
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      // depdb_dep_options
+      //
+
+      inline const path& depdb_dep_options::
+      file () const
+      {
+        return this->file_;
+      }
+
+      inline path& depdb_dep_options::
+      file ()
+      {
+        return this->file_;
+      }
+
+      inline void depdb_dep_options::
+      file (const path& x)
+      {
+        this->file_ = x;
+      }
+
+      inline bool depdb_dep_options::
+      file_specified () const
+      {
+        return this->file_specified_;
+      }
+
+      inline void depdb_dep_options::
+      file_specified (bool x)
+      {
+        this->file_specified_ = x;
+      }
+
+      inline const string& depdb_dep_options::
+      format () const
+      {
+        return this->format_;
+      }
+
+      inline string& depdb_dep_options::
+      format ()
+      {
+        return this->format_;
+      }
+
+      inline void depdb_dep_options::
+      format (const string& x)
+      {
+        this->format_ = x;
+      }
+
+      inline bool depdb_dep_options::
+      format_specified () const
+      {
+        return this->format_specified_;
+      }
+
+      inline void depdb_dep_options::
+      format_specified (bool x)
+      {
+        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;
+      }
+    }
+  }
+}
+
+// Begin epilogue.
+//
+//
+// End epilogue.
diff --git a/libbuild2/build/script/builtin.cli b/libbuild2/build/script/builtin.cli
new file mode 100644
index 0000000..3ed3659
--- /dev/null
+++ b/libbuild2/build/script/builtin.cli
@@ -0,0 +1,32 @@
+// file      : libbuild2/build/script/builtin.cli
+// license   : MIT; see accompanying LICENSE file
+
+include <libbuild2/types.hxx>;
+
+// Note that options in this file are undocumented because we generate neither
+// the usage printing code nor man pages. Instead, they are documented in the
+// manual.
+//
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      // Pseudo-builtin options.
+      //
+      class depdb_dep_options
+      {
+        // 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 217fa11..67dbf69 100644
--- a/libbuild2/build/script/parser.cxx
+++ b/libbuild2/build/script/parser.cxx
@@ -3,13 +3,22 @@
 
 #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>
 
 #include <libbuild2/build/script/lexer.hxx>
 #include <libbuild2/build/script/runner.hxx>
+#include <libbuild2/build/script/builtin-options.hxx>
 
 using namespace std;
 using namespace butl;
@@ -125,6 +134,8 @@ namespace build2
         // Save the custom dependency change tracking lines, if present.
         //
         s.depdb_clear = depdb_clear_.has_value ();
+        if (depdb_dyndep_)
+          s.depdb_dyndep = depdb_dyndep_->second;
         s.depdb_preamble = move (depdb_preamble_);
 
         return s;
@@ -487,7 +498,11 @@ namespace build2
             next (t, tt);
 
             if (tt != type::word ||
-                (v != "clear" && v != "hash" && v != "string" && v != "env"))
+                (v != "clear"  &&
+                 v != "hash"   &&
+                 v != "string" &&
+                 v != "env"    &&
+                 v != "dyndep"))
             {
               fail (get_location (t))
                 << "expected 'depdb' builtin command instead of " << t;
@@ -527,12 +542,39 @@ namespace build2
               // the referenced variable list, since it won't be used.
               //
               depdb_clear_ = l;
-              save_line_   = nullptr;
+              save_line_ = nullptr;
 
               script_->vars.clear ();
             }
             else
             {
+              // Verify depdb-dyndep is last.
+              //
+              if (v == "dyndep")
+              {
+                // 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_dyndep_)
+                  depdb_dyndep_ = make_pair (l, depdb_preamble_.size ());
+                else
+                  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_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.
               //
               // Note that at this (pre-parsing) stage we cannot evaluate if
@@ -885,114 +927,140 @@ namespace build2
       }
 
       void parser::
-      execute_depdb_preamble (const scope& rs, const scope& bs,
-                              environment& e, const script& s, runner& r,
-                              depdb& dd)
+      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,
+                           bool* deferred_failure,
+                           optional<timestamp> mt)
       {
-        tracer trace ("execute_depdb_preamble");
+        tracer trace ("exec_depdb_preamble");
 
         // The only valid lines in the depdb preamble are the depdb builtin
         // itself as well as the variable assignments, including via the set
         // builtin.
 
-        pre_exec (rs, bs, e, &s, &r);
+        pre_exec (*bs.root_scope (), bs, e, &s, &r);
 
         // Let's "wrap up" the objects we operate upon into the single object
         // to rely on "small function object" optimization.
         //
         struct
         {
+          tracer& trace;
+
+          action a;
+          const scope& bs;
+          const file& t;
+
           environment& env;
           const script& scr;
+
           depdb& dd;
-          tracer& trace;
-        } ctx {e, s, dd, trace};
-
-        auto exec_cmd = [&ctx, this]
-                        (token& t,
-                         build2::script::token_type& tt,
-                         size_t li,
-                         bool /* single */,
-                         const location& ll)
+          bool* update;
+          bool* deferred_failure;
+          optional<timestamp> 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,
+                                       size_t li,
+                                       bool /* single */,
+                                       const location& ll)
         {
+          // Note that we never reset the line index to zero (as we do in
+          // execute_body()) assuming that there are some script body
+          // commands to follow.
+          //
           if (tt == type::word && t.value == "depdb")
           {
-            names ns (exec_special (t, tt));
+            next (t, tt);
 
             // This should have been enforced during pre-parsing.
             //
-            assert (!ns.empty ()); // <cmd> ... <newline>
+            assert (tt == type::word); // <cmd> ... <newline>
 
-            const string& cmd (ns[0].value);
+            string cmd (move (t.value));
 
-            if (cmd == "hash")
+            if (cmd == "dyndep")
             {
-              sha256 cs;
-              for (auto i (ns.begin () + 1); i != ns.end (); ++i) // Skip <cmd>.
-                to_checksum (cs, *i);
-
-              if (ctx.dd.expect (cs.string ()) != nullptr)
-                l4 ([&] {
-                    ctx.trace (ll)
-                      << "'depdb hash' argument change forcing update of "
-                      << ctx.env.target;});
+              // 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 if (cmd == "string")
+            else
             {
-              string s;
-              try
-              {
-                s = convert<string> (
-                  names (make_move_iterator (ns.begin () + 1),
-                         make_move_iterator (ns.end ())));
-              }
-              catch (const invalid_argument& e)
+              names ns (exec_special (t, tt, true /* skip <cmd> */));
+
+              if (cmd == "hash")
               {
-                fail (ll) << "invalid 'depdb string' argument: " << e;
+                sha256 cs;
+                for (const name& n: ns)
+                  to_checksum (cs, n);
+
+                if (data.dd.expect (cs.string ()) != nullptr)
+                  l4 ([&] {
+                      data.trace (ll)
+                        << "'depdb hash' argument change forcing update of "
+                        << data.t;});
               }
-
-              if (ctx.dd.expect (s) != nullptr)
-                l4 ([&] {
-                    ctx.trace (ll)
-                      << "'depdb string' argument change forcing update of "
-                      << ctx.env.target;});
-            }
-            else if (cmd == "env")
-            {
-              sha256 cs;
-              const char* pf ("invalid 'depdb env' argument: ");
-
-              try
+              else if (cmd == "string")
               {
-                // Skip <cmd>.
-                //
-                for (auto i (ns.begin () + 1); i != ns.end (); ++i)
+                string s;
+                try
+                {
+                  s = convert<string> (move (ns));
+                }
+                catch (const invalid_argument& e)
                 {
-                  string vn (convert<string> (move (*i)));
-                  build2::script::verify_environment_var_name (vn, pf, ll);
-                  hash_environment (cs, vn);
+                  fail (ll) << "invalid 'depdb string' argument: " << e;
                 }
+
+                if (data.dd.expect (s) != nullptr)
+                  l4 ([&] {
+                      data.trace (ll)
+                        << "'depdb string' argument change forcing update of "
+                        << data.t;});
               }
-              catch (const invalid_argument& e)
+              else if (cmd == "env")
               {
-                fail (ll) << pf << e;
-              }
+                sha256 cs;
+                const char* pf ("invalid 'depdb env' argument: ");
 
-              if (ctx.dd.expect (cs.string ()) != nullptr)
-                l4 ([&] {
-                    ctx.trace (ll)
-                      << "'depdb env' environment change forcing update of "
-                      << ctx.env.target;});
+                try
+                {
+                  for (name& n: ns)
+                  {
+                    string vn (convert<string> (move (n)));
+                    build2::script::verify_environment_var_name (vn, pf, ll);
+                    hash_environment (cs, vn);
+                  }
+                }
+                catch (const invalid_argument& e)
+                {
+                  fail (ll) << pf << e;
+                }
+
+                if (data.dd.expect (cs.string ()) != nullptr)
+                  l4 ([&] {
+                      data.trace (ll)
+                        << "'depdb env' environment change forcing update of "
+                        << data.t;});
+              }
+              else
+                assert (false);
             }
-            else
-              assert (false);
           }
           else
           {
-            // Note that we don't reset the line index to zero (as we do in
-            // execute_body()) assuming that there are some script body
-            // commands to follow.
-            //
             command_expr ce (
               parse_command_line (t, static_cast<token_type&> (tt)));
 
@@ -1006,7 +1074,7 @@ namespace build2
                                   p.recall.string () == "set";
                          }) == ce.end ())
             {
-              const replay_tokens& rt (ctx.scr.depdb_preamble.back ().tokens);
+              const replay_tokens& rt (data.scr.depdb_preamble.back ().tokens);
               assert (!rt.empty ());
 
               fail (ll) << "disallowed command in depdb preamble" <<
@@ -1019,7 +1087,7 @@ namespace build2
           }
         };
 
-        exec_lines (s.depdb_preamble, exec_cmd);
+        exec_lines (begin, end, exec_cmd);
       }
 
       void parser::
@@ -1051,7 +1119,7 @@ namespace build2
       }
 
       void parser::
-      exec_lines (const lines& lns,
+      exec_lines (lines_iterator begin, lines_iterator end,
                   const function<exec_cmd_function>& exec_cmd)
       {
         // Note that we rely on "small function object" optimization for the
@@ -1090,25 +1158,23 @@ namespace build2
           return runner_->run_if (*environment_, ce, li, ll);
         };
 
-        build2::script::parser::exec_lines (lns.begin (), lns.end (),
+        build2::script::parser::exec_lines (begin, end,
                                             exec_set, exec_cmd, exec_if,
                                             environment_->exec_line,
                                             &environment_->var_pool);
       }
 
       names parser::
-      exec_special (token& t, build2::script::token_type& tt,
-                    bool omit_builtin)
+      exec_special (token& t, build2::script::token_type& tt, bool skip_first)
       {
-        if (omit_builtin)
+        if (skip_first)
         {
           assert (tt != type::newline && tt != type::eos);
-
           next (t, tt);
         }
 
         return tt != type::newline && tt != type::eos
-               ? parse_names (t, tt, pattern_mode::expand)
+               ? parse_names (t, tt, pattern_mode::ignore)
                : names ();
       }
 
@@ -1134,6 +1200,649 @@ namespace build2
         return r;
       }
 
+      void parser::
+      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().
+        //
+        depdb_dep_options ops;
+        bool prog (false);
+        {
+          auto& t (lt);
+          auto& tt (ltt);
+
+          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;
+
+          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));
+
+            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)
+            {
+              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 ();
+          }
+
+          if (prog)
+          {
+            next (t, tt); // Skip '--'.
+
+            if (tt == type::newline || tt == type::eos)
+              fail (t) << "depdb dyndep: 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;
+          }
+        }
+
+        // Get the default prerequisite type falling back to file{} if not
+        // specified.
+        //
+        // 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 ())
+        {
+          const string& t (ops.default_prereq_type ());
+
+          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, &ll, &t] (const diag_record& dr)
+          {
+            if (verb != 0)
+              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);
+
+        for (bool restart (true), first_run (true); restart; cache = false)
+        {
+          restart = false;
+
+          if (cache)
+          {
+            // If any, this is always the first run.
+            //
+            assert (skip_count == 0);
+
+            // We should always end with a blank line.
+            //
+            for (;;)
+            {
+              string* l (dd.read ());
+
+              // If the line is invalid, run the compiler.
+              //
+              if (l == nullptr)
+              {
+                restart = true;
+                break;
+              }
+
+              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";
+            }
+
+            // 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);
+
+            // 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);
+              }
+            }
+
+            ifdstream ifs (ifdstream::badbit);
+            if (file)
+            try
+            {
+              ifs.open (*file);
+            }
+            catch (const io_error& e)
+            {
+              fail (ll) << "unable to open file " << *file << ": " << e;
+            }
+
+            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().
       //
       bool parser::
diff --git a/libbuild2/build/script/parser.hxx b/libbuild2/build/script/parser.hxx
index b737a13..da15509 100644
--- a/libbuild2/build/script/parser.hxx
+++ b/libbuild2/build/script/parser.hxx
@@ -8,7 +8,6 @@
 #include <libbuild2/forward.hxx>
 #include <libbuild2/utility.hxx>
 
-#include <libbuild2/depdb.hxx>
 #include <libbuild2/diagnostics.hxx>
 
 #include <libbuild2/script/parser.hxx>
@@ -82,21 +81,51 @@ 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& root, const scope& base,
                       environment&, const script&, runner&,
                       bool enter = true, bool leave = true);
 
 
+        // 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
         // runner's enter() function is called before the first preamble/body
         // command execution and leave() -- after the last command.
         //
         void
-        execute_depdb_preamble (const scope& root, const scope& base,
-                                environment&, const script&, runner&,
-                                depdb&);
+        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 (
+            a, base, t,
+            e, s, r,
+            b,
+            (s.depdb_dyndep
+             ? b + *s.depdb_dyndep
+             : s.depdb_preamble.end ()),
+            dd);
+        }
 
+        void
+        execute_depdb_preamble_dyndep (
+          action a, const scope& base, file& t,
+          environment& e, const script& s, runner& r,
+          depdb& dd, bool& update, bool& deferred_failure, timestamp mt)
+        {
+          exec_depdb_preamble (
+            a, base, t,
+            e, s, r,
+            s.depdb_preamble.begin () + *s.depdb_dyndep,
+            s.depdb_preamble.end (),
+            dd, &update, &deferred_failure, mt);
+        }
 
         // Parse a special builtin line into names, performing the variable
         // and pattern expansions. If omit_builtin is true, then omit the
@@ -115,12 +144,38 @@ namespace build2
         pre_exec (const scope& root, const scope& base,
                   environment&, const script*, runner*);
 
+        using lines_iterator = lines::const_iterator;
+
+        void
+        exec_lines (lines_iterator, lines_iterator,
+                    const function<exec_cmd_function>&);
+
         void
-        exec_lines (const lines&, const function<exec_cmd_function>&);
+        exec_lines (const lines& l, const function<exec_cmd_function>& c)
+        {
+          exec_lines (l.begin (), l.end (), c);
+        }
 
         names
-        exec_special (token& t, build2::script::token_type& tt,
-                      bool omit_builtin = true);
+        exec_special (token&, build2::script::token_type&, bool skip_first);
+
+        void
+        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_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.
         //
@@ -219,8 +274,14 @@ namespace build2
         // depdb env <var-names> - Track the environment variables change as a
         //                         hash.
         //
-        optional<location> depdb_clear_;    // 'depdb clear' location if any.
-        lines              depdb_preamble_; // Note: excludes 'depdb clear'.
+        // 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_dyndep_;   // depdb-dyndep location/position.
+        lines              depdb_preamble_; // Note: excluding depdb-clear.
 
         // If present, the first impure function called in the body of the
         // script that performs update of a file-based target.
diff --git a/libbuild2/build/script/runner.hxx b/libbuild2/build/script/runner.hxx
index 431c446..558de9b 100644
--- a/libbuild2/build/script/runner.hxx
+++ b/libbuild2/build/script/runner.hxx
@@ -53,7 +53,7 @@ namespace build2
       // Run command expressions.
       //
       // In dry-run mode don't run the expressions unless they are if-
-      // conditions or execute the set or exit builtins, but prints them at
+      // conditions or execute the set or exit builtins, but print them at
       // verbosity level 2 and up.
       //
       class default_runner: public runner
diff --git a/libbuild2/build/script/script.hxx b/libbuild2/build/script/script.hxx
index e11cb45..9d7567c 100644
--- a/libbuild2/build/script/script.hxx
+++ b/libbuild2/build/script/script.hxx
@@ -29,6 +29,10 @@ namespace build2
       using build2::script::deadline;
       using build2::script::timeout;
 
+      // Forward declarations.
+      //
+      class default_runner;
+
       // Notes:
       //
       // - Once parsed, the script can be executed in multiple threads with
@@ -70,9 +74,10 @@ namespace build2
         // The script's custom dependency change tracking lines (see the
         // script parser for details).
         //
-        bool       depdb_clear;
-        lines_type depdb_preamble;
-        bool       depdb_preamble_temp_dir = false; // True if references $~.
+        bool             depdb_clear;
+        optional<size_t> depdb_dyndep;   // Position of first depdb-dyndep.
+        lines_type       depdb_preamble;
+        bool             depdb_preamble_temp_dir = false; // True if refs $~.
 
         location start_loc;
         location end_loc;
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