Add ability to skip external modules during bootstrap (--no-external-modules)

9 files changed, 108 insertions, 34 deletions

diff --git a/build2/b-options.cxx b/build2/b-options.cxx
index 95772bb..316d7ad 100644
--- a/build2/b-options.cxx
+++ b/build2/b-options.cxx
@@ -698,6 +698,7 @@ namespace build2
     serial_stop_ (),
     dry_run_ (),
     match_only_ (),
+    no_external_modules_ (),
     structured_result_ (),
     mtime_check_ (),
     no_mtime_check_ (),
@@ -898,6 +899,12 @@ namespace build2
         this->match_only_, a.match_only_);
     }
 
+    if (a.no_external_modules_)
+    {
+      ::build2::cl::parser< bool>::merge (
+        this->no_external_modules_, a.no_external_modules_);
+    }
+
     if (a.structured_result_)
     {
       ::build2::cl::parser< bool>::merge (
@@ -1110,6 +1117,12 @@ namespace build2
        << "                      mode is primarily useful for profiling." << ::std::endl;
 
     os << std::endl
+       << "\033[1m--no-external-modules\033[0m Don't load external modules during project bootstrap." << ::std::endl
+       << "                      Note that this option can only be used with" << ::std::endl
+       << "                      meta-operations that do not load the project's" << ::std::endl
+       << "                      \033[1mbuildfiles\033[0m, such as \033[1minfo\033[0m." << ::std::endl;
+
+    os << std::endl
        << "\033[1m--structured-result\033[0m   Write the result of execution in a structured form. In" << ::std::endl
        << "                      this mode, instead of printing to \033[1mSTDERR\033[0m diagnostics" << ::std::endl
        << "                      messages about the outcome of executing actions on" << ::std::endl
@@ -1267,6 +1280,8 @@ namespace build2
       &::build2::cl::thunk< options, bool, &options::dry_run_ >;
       _cli_options_map_["--match-only"] =
       &::build2::cl::thunk< options, bool, &options::match_only_ >;
+      _cli_options_map_["--no-external-modules"] =
+      &::build2::cl::thunk< options, bool, &options::no_external_modules_ >;
       _cli_options_map_["--structured-result"] =
       &::build2::cl::thunk< options, bool, &options::structured_result_ >;
       _cli_options_map_["--mtime-check"] =
diff --git a/build2/b-options.hxx b/build2/b-options.hxx
index c6f1f59..d55dd36 100644
--- a/build2/b-options.hxx
+++ b/build2/b-options.hxx
@@ -526,6 +526,9 @@ namespace build2
     match_only () const;
 
     const bool&
+    no_external_modules () const;
+
+    const bool&
     structured_result () const;
 
     const bool&
@@ -628,6 +631,7 @@ namespace build2
     bool serial_stop_;
     bool dry_run_;
     bool match_only_;
+    bool no_external_modules_;
     bool structured_result_;
     bool mtime_check_;
     bool no_mtime_check_;
diff --git a/build2/b-options.ixx b/build2/b-options.ixx
index 6444aa9..1d41af2 100644
--- a/build2/b-options.ixx
+++ b/build2/b-options.ixx
@@ -405,6 +405,12 @@ namespace build2
   }
 
   inline const bool& options::
+  no_external_modules () const
+  {
+    return this->no_external_modules_;
+  }
+
+  inline const bool& options::
   structured_result () const
   {
     return this->structured_result_;
diff --git a/build2/b.cli b/build2/b.cli
index 57640b6..a03e9cc 100644
--- a/build2/b.cli
+++ b/build2/b.cli
@@ -535,6 +535,13 @@ namespace build2
        useful for profiling."
     }
 
+    bool --no-external-modules
+    {
+      "Don't load external modules during project bootstrap. Note that this
+       option can only be used with meta-operations that do not load the
+       project's \cb{buildfiles}, such as \cb{info}."
+    }
+
     bool --structured-result
     {
       "Write the result of execution in a structured form. In this mode,
diff --git a/build2/b.cxx b/build2/b.cxx
index b7e6708..18326cc 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -785,6 +785,7 @@ main (int argc, char* argv[])
       ctx.reset (new context (sched,
                               mutexes,
                               ops.match_only (),
+                              ops.no_external_modules (),
                               ops.dry_run (),
                               !ops.serial_stop () /* keep_going */,
                               cmd_vars));
diff --git a/libbuild2/context.cxx b/libbuild2/context.cxx
index d62965c..b78cd27 100644
--- a/libbuild2/context.cxx
+++ b/libbuild2/context.cxx
@@ -59,6 +59,7 @@ namespace build2
   context (scheduler& s,
            global_mutexes& ms,
            bool mo,
+           bool nem,
            bool dr,
            bool kg,
            const strings& cmd_vars,
@@ -68,6 +69,7 @@ namespace build2
         sched (s),
         mutexes (ms),
         match_only (mo),
+        no_external_modules (nem),
         dry_run_option (dr),
         keep_going (kg),
         phase_mutex (*this),
diff --git a/libbuild2/context.hxx b/libbuild2/context.hxx
index c4e1259..0790355 100644
--- a/libbuild2/context.hxx
+++ b/libbuild2/context.hxx
@@ -146,6 +146,10 @@ namespace build2
     //
     bool match_only;
 
+    // Skip booting external modules flag (see --no-external-modules).
+    //
+    bool no_external_modules;
+
     // Dry run flag (see --dry-run|-n).
     //
     // This flag is set (based on dry_run_option) only for the final execute
@@ -479,6 +483,7 @@ namespace build2
     context (scheduler&,
              global_mutexes&,
              bool match_only = false,
+             bool no_external_modules = false,
              bool dry_run = false,
              bool keep_going = true,
              const strings& cmd_vars = {},
diff --git a/libbuild2/file.cxx b/libbuild2/file.cxx
index 2660b9e..67aeb77 100644
--- a/libbuild2/file.cxx
+++ b/libbuild2/file.cxx
@@ -1431,6 +1431,8 @@ namespace build2
   {
     tracer trace ("load_root");
 
+    context& ctx (root.ctx);
+
     const dir_path& out_root (root.out_path ());
     const dir_path& src_root (root.src_path ());
 
@@ -1442,6 +1444,10 @@ namespace build2
     if (root.buildfiles.find (f) != root.buildfiles.end ())
       return;
 
+    if (ctx.no_external_modules)
+      fail << "attempt to load project " << root << " after skipped loading "
+           << "external modules";
+
     // First load outer roots, if any.
     //
     if (scope* rs = root.parent_scope ()->root_scope ())
@@ -1483,7 +1489,7 @@ namespace build2
 
     // Reuse the parser to accumulate the configuration variable information.
     //
-    parser p (root.ctx, load_stage::root);
+    parser p (ctx, load_stage::root);
 
     if (he) {source_hooks (p, root, hd, true  /* pre */); p.reset ();}
     if (fe) {source_once (p, root, root, f, root);}
diff --git a/libbuild2/module.cxx b/libbuild2/module.cxx
index 11b32cb..14cf183 100644
--- a/libbuild2/module.cxx
+++ b/libbuild2/module.cxx
@@ -81,6 +81,7 @@ namespace build2
       new context (ctx.sched,
                    ctx.mutexes,
                    false,                    /* match_only */
+                   false,                    /* no_external_modules */
                    false,                    /* dry_run */
                    ctx.keep_going,
                    ctx.global_var_overrides, /* cmd_vars */
@@ -238,7 +239,11 @@ namespace build2
 #endif
     const string& mod,
     const location& loc,
-    bool /* boot */,
+#if defined(BUILD2_BOOTSTRAP) || defined(LIBBUILD2_STATIC_BUILD)
+    bool,
+#else
+    bool boot,
+#endif
     bool opt)
   {
     tracer trace ("import_module");
@@ -251,6 +256,26 @@ namespace build2
     else if (mod == "install") return &install::build2_install_load;
     else if (mod == "test")    return &test::build2_test_load;
 
+    module_load_function* r (nullptr);
+
+    // No dynamic loading of build system modules during bootstrap or if
+    // statically-linked..
+    //
+#if defined(BUILD2_BOOTSTRAP) || defined(LIBBUILD2_STATIC_BUILD)
+    if (!opt)
+    {
+      fail (loc) << "unknown build system module " << mod <<
+#ifdef BUILD2_BOOTSTRAP
+        info << "running bootstrap build system";
+#else
+        info << "running statically-linked build system";
+#endif
+    }
+#else
+    context& ctx (bs.ctx);
+
+    bool bundled (bundled_module (mod));
+
     // Note that importing external modules during bootstrap is problematic
     // since we haven't loaded config.build nor entered non-global variable
     // overrides. We used to just not support external modules that require
@@ -287,28 +312,20 @@ namespace build2
     // And another case is the bdep-sync hook which also doesn't have the
     // global overrides propagated to it.
     //
-    // It does feel right to propagate global overrides to all the nested
-    // build system invocations. Maybe we should set an environment variable?
-
-    module_load_function* r (nullptr);
-
-    // No dynamic loading of build system modules during bootstrap or if
-    // statically-linked..
-    //
-#if defined(BUILD2_BOOTSTRAP) || defined(LIBBUILD2_STATIC_BUILD)
-    if (!opt)
-    {
-      fail (loc) << "unknown build system module " << mod <<
-#ifdef BUILD2_BOOTSTRAP
-        info << "running bootstrap build system";
-#else
-        info << "running statically-linked build system";
-#endif
-    }
-#else
-    context& ctx (bs.ctx);
-
-    bool bundled (bundled_module (mod));
+    // And it turns out the story does not end here: without an external
+    // module we cannot do info or dist. So to support this we now allow
+    // skipping of loading of external modules (for dist this is only part of
+    // the solution with the other part being the bootstrap mode). While no
+    // doubt a hack, it feels like this is the time to cut of this complexity
+    // escalation. Essentially, we are saying external module that require
+    // bootstrap must be prepared to be skipped if the project is only being
+    // bootstrapped. Note also that the fact that a module boot was skipped
+    // can be detected by checking the module's *.booted variable. In case of
+    // a skip it will be false, as opposed to true if the module was booted
+    // and undefined if the module was not mentioned.
+    //
+    if (boot && !bundled && ctx.no_external_modules)
+      return nullptr;
 
     // See if we can import a target for this module.
     //
@@ -570,7 +587,14 @@ namespace build2
                        << mmod;
         }
         else
+        {
+          // Reduce skipped external module to optional.
+          //
+          if (boot)
+            opt = true;
+
           i = loaded_modules.emplace (move (mmod), nullptr).first;
+        }
       }
     }
 
@@ -616,23 +640,27 @@ namespace build2
 
     // Otherwise search for this module.
     //
-    const module_functions& mf (
-      *find_module (rs, mod, loc, true /* boot */, false /* optional */));
+    // Note that find_module() may return NULL in case of a skipped external
+    // module.
+    //
+    const module_functions* mf (
+      find_module (rs, mod, loc, true /* boot */, false /* optional */));
 
-    if (mf.boot == nullptr)
-      fail (loc) << "build system module " << mod << " should not be loaded "
-                 << "during bootstrap";
+    if (mf != nullptr)
+    {
+      if (mf->boot == nullptr)
+        fail (loc) << "build system module " << mod << " should not be loaded "
+                   << "during bootstrap";
 
-    lm.push_back (module_state {loc, mod, mf.init, nullptr, nullopt});
-    i = lm.end () - 1;
+      lm.push_back (module_state {loc, mod, mf->init, nullptr, nullopt});
+      i = lm.end () - 1;
 
-    {
       module_boot_extra e {nullptr, module_boot_init::before};
 
       // Note: boot() can load additional modules invalidating the iterator.
       //
       size_t j (i - lm.begin ());
-      mf.boot (rs, loc, e);
+      mf->boot (rs, loc, e);
       i = lm.begin () + j;
 
       if (e.module != nullptr)
@@ -641,7 +669,7 @@ namespace build2
       i->boot_init = e.init;
     }
 
-    rs.assign (rs.var_pool ().insert (mod + ".booted")) = true;
+    rs.assign (rs.var_pool ().insert (mod + ".booted")) = (mf != nullptr);
   }
 
   module_state*