Rename module_base to module, redo module boot/init argument passing

23 files changed, 168 insertions, 209 deletions

diff --git a/libbuild2/bash/init.cxx b/libbuild2/bash/init.cxx
index ed84265..0dc4bab 100644
--- a/libbuild2/bash/init.cxx
+++ b/libbuild2/bash/init.cxx
@@ -27,10 +27,9 @@ namespace build2
     init (scope& rs,
           scope& bs,
           const location& l,
-          unique_ptr<module_base>&,
           bool first,
           bool,
-          const variable_map&)
+          module_init_extra&)
     {
       tracer trace ("bash::init");
       l5 ([&]{trace << "for " << bs;});
diff --git a/libbuild2/bin/init.cxx b/libbuild2/bin/init.cxx
index 2bb96e8..069315f 100644
--- a/libbuild2/bin/init.cxx
+++ b/libbuild2/bin/init.cxx
@@ -42,10 +42,9 @@ namespace build2
     vars_init (scope& rs,
                scope&,
                const location&,
-               unique_ptr<module_base>&,
                bool first,
                bool,
-               const variable_map&)
+               module_init_extra&)
     {
       tracer trace ("bin::vars_init");
       l5 ([&]{trace << "for " << rs;});
@@ -146,10 +145,9 @@ namespace build2
     config_init (scope& rs,
                  scope& bs,
                  const location& loc,
-                 unique_ptr<module_base>&,
                  bool first,
                  bool,
-                 const variable_map& hints)
+                 module_init_extra& extra)
     {
       tracer trace ("bin::config_init");
       l5 ([&]{trace << "for " << bs;});
@@ -288,7 +286,7 @@ namespace build2
           bool hint (false);
           if (!l)
           {
-            if (auto hl = hints[var])
+            if (auto hl = extra.hints[var])
             {
               l = hl;
               hint = true;
@@ -364,7 +362,7 @@ namespace build2
           //
           if (!l)
           {
-            if (auto hl = hints[var])
+            if (auto hl = extra.hints[var])
               l = hl;
           }
 
@@ -412,17 +410,16 @@ namespace build2
     init (scope& rs,
           scope& bs,
           const location& loc,
-          unique_ptr<module_base>&,
           bool first,
           bool,
-          const variable_map& hints)
+          module_init_extra& extra)
     {
       tracer trace ("bin::init");
       l5 ([&]{trace << "for " << bs;});
 
       // Load bin.config.
       //
-      load_module (rs, rs, "bin.config", loc, hints);
+      load_module (rs, rs, "bin.config", loc, extra.hints);
 
       // Cache some config values we will be needing below.
       //
@@ -567,17 +564,16 @@ namespace build2
     ar_config_init (scope& rs,
                     scope& bs,
                     const location& loc,
-                    unique_ptr<module_base>&,
                     bool first,
                     bool,
-                    const variable_map& hints)
+                    module_init_extra& extra)
     {
       tracer trace ("bin::ar_config_init");
       l5 ([&]{trace << "for " << bs;});
 
       // Make sure bin.config is loaded.
       //
-      load_module (rs, bs, "bin.config", loc, hints);
+      load_module (rs, bs, "bin.config", loc, extra.hints);
 
       // Enter configuration variables.
       //
@@ -715,18 +711,17 @@ namespace build2
     ar_init (scope& rs,
              scope& bs,
              const location& loc,
-             unique_ptr<module_base>&,
              bool,
              bool,
-             const variable_map& hints)
+             module_init_extra& extra)
     {
       tracer trace ("bin::ar_init");
       l5 ([&]{trace << "for " << bs;});
 
       // Make sure the bin core and ar.config are loaded.
       //
-      load_module (rs, bs, "bin",           loc, hints);
-      load_module (rs, bs, "bin.ar.config", loc, hints);
+      load_module (rs, bs, "bin",           loc, extra.hints);
+      load_module (rs, bs, "bin.ar.config", loc, extra.hints);
 
       return true;
     }
@@ -735,17 +730,16 @@ namespace build2
     ld_config_init (scope& rs,
                     scope& bs,
                     const location& loc,
-                    unique_ptr<module_base>&,
                     bool first,
                     bool,
-                    const variable_map& hints)
+                    module_init_extra& extra)
     {
       tracer trace ("bin::ld_config_init");
       l5 ([&]{trace << "for " << bs;});
 
       // Make sure bin.config is loaded.
       //
-      load_module (rs, rs, "bin.config", loc, hints);
+      load_module (rs, rs, "bin.config", loc, extra.hints);
 
       // Enter configuration variables.
       //
@@ -808,18 +802,17 @@ namespace build2
     ld_init (scope& rs,
              scope& bs,
              const location& loc,
-             unique_ptr<module_base>&,
              bool,
              bool,
-             const variable_map& hints)
+             module_init_extra& extra)
     {
       tracer trace ("bin::ld_init");
       l5 ([&]{trace << "for " << bs;});
 
       // Make sure the bin core and ld.config are loaded.
       //
-      load_module (rs, bs, "bin",           loc, hints);
-      load_module (rs, bs, "bin.ld.config", loc, hints);
+      load_module (rs, bs, "bin",           loc, extra.hints);
+      load_module (rs, bs, "bin.ld.config", loc, extra.hints);
 
       const string& lid (cast<string> (rs["bin.ld.id"]));
 
@@ -841,17 +834,16 @@ namespace build2
     rc_config_init (scope& rs,
                     scope& bs,
                     const location& loc,
-                    unique_ptr<module_base>&,
                     bool first,
                     bool,
-                    const variable_map& hints)
+                    module_init_extra& extra)
     {
       tracer trace ("bin::rc_config_init");
       l5 ([&]{trace << "for " << bs;});
 
       // Make sure bin.config is loaded.
       //
-      load_module (rs, bs, "bin.config", loc, hints);
+      load_module (rs, bs, "bin.config", loc, extra.hints);
 
       // Enter configuration variables.
       //
@@ -914,18 +906,17 @@ namespace build2
     rc_init (scope& rs,
              scope& bs,
              const location& loc,
-             unique_ptr<module_base>&,
              bool,
              bool,
-             const variable_map& hints)
+             module_init_extra& extra)
     {
       tracer trace ("bin::rc_init");
       l5 ([&]{trace << "for " << bs;});
 
       // Make sure the bin core and rc.config are loaded.
       //
-      load_module (rs, bs, "bin",           loc, hints);
-      load_module (rs, bs, "bin.rc.config", loc, hints);
+      load_module (rs, bs, "bin",           loc, extra.hints);
+      load_module (rs, bs, "bin.rc.config", loc, extra.hints);
 
       return true;
     }
diff --git a/libbuild2/c/init.cxx b/libbuild2/c/init.cxx
index a220169..5939d4c 100644
--- a/libbuild2/c/init.cxx
+++ b/libbuild2/c/init.cxx
@@ -131,10 +131,9 @@ namespace build2
     guess_init (scope& rs,
                 scope& bs,
                 const location& loc,
-                unique_ptr<module_base>& mod,
                 bool,
                 bool,
-                const variable_map& hints)
+                module_init_extra& extra)
     {
       tracer trace ("c::guess_init");
       l5 ([&]{trace << "for " << bs;});
@@ -258,10 +257,9 @@ namespace build2
       //
       vp.insert_alias (d.c_runtime, "c.runtime");
 
-      assert (mod == nullptr);
-      config_module* m (new config_module (move (d)));
-      mod.reset (m);
-      m->guess (rs, loc, hints);
+      auto& m (extra.set_module (new config_module (move (d))));
+      m.guess (rs, loc, extra.hints);
+
       return true;
     }
 
@@ -269,10 +267,9 @@ namespace build2
     config_init (scope& rs,
                  scope& bs,
                  const location& loc,
-                 unique_ptr<module_base>&,
                  bool,
                  bool,
-                 const variable_map& hints)
+                 module_init_extra& extra)
     {
       tracer trace ("c::config_init");
       l5 ([&]{trace << "for " << bs;});
@@ -282,11 +279,11 @@ namespace build2
       if (&rs != &bs)
         fail (loc) << "c.config module must be loaded in project root";
 
-      // Load c.guess.
+      // Load c.guess and share its module instance as ours.
       //
-      auto& cm (load_module<config_module> (rs, rs, "c.guess", loc, hints));
+      extra.module = load_module (rs, rs, "c.guess", loc, extra.hints);
+      extra.module_as<config_module> ().init (rs, loc, extra.hints);
 
-      cm.init (rs, loc, hints);
       return true;
     }
 
@@ -307,10 +304,9 @@ namespace build2
     init (scope& rs,
           scope& bs,
           const location& loc,
-          unique_ptr<module_base>& mod,
           bool,
           bool,
-          const variable_map& hints)
+          module_init_extra& extra)
     {
       tracer trace ("c::init");
       l5 ([&]{trace << "for " << bs;});
@@ -322,11 +318,8 @@ namespace build2
 
       // Load c.config.
       //
-      // @@ TODO: move guess to config and use return value?
-      //
-      load_module (rs, rs, "c.config", loc, hints);
-
-      config_module& cm (*rs.find_module<config_module> ("c.guess"));
+      auto& cm (
+        load_module<config_module> (rs, rs, "c.config", loc, extra.hints));
 
       cc::data d {
         cm,
@@ -363,10 +356,9 @@ namespace build2
         inc
       };
 
-      assert (mod == nullptr);
-      module* m;
-      mod.reset (m = new module (move (d)));
-      m->init (rs, loc, hints);
+      auto& m (extra.set_module (new module (move (d))));
+      m.init (rs, loc, extra.hints);
+
       return true;
     }
 
diff --git a/libbuild2/cc/init.cxx b/libbuild2/cc/init.cxx
index 0536e0f..436de3b 100644
--- a/libbuild2/cc/init.cxx
+++ b/libbuild2/cc/init.cxx
@@ -62,10 +62,9 @@ namespace build2
     core_vars_init (scope& rs,
                     scope&,
                     const location& loc,
-                    unique_ptr<module_base>&,
                     bool first,
                     bool,
-                    const variable_map&)
+                    module_init_extra&)
     {
       tracer trace ("cc::core_vars_init");
       l5 ([&]{trace << "for " << rs;});
@@ -159,16 +158,17 @@ namespace build2
     core_guess_init (scope& rs,
                      scope&,
                      const location& loc,
-                     unique_ptr<module_base>&,
                      bool first,
                      bool,
-                     const variable_map& h)
+                     module_init_extra& extra)
     {
       tracer trace ("cc::core_guess_init");
       l5 ([&]{trace << "for " << rs;});
 
       assert (first);
 
+      auto& h (extra.hints);
+
       // Load cc.core.vars.
       //
       load_module (rs, rs, "cc.core.vars", loc);
@@ -232,10 +232,9 @@ namespace build2
     core_config_init (scope& rs,
                       scope&,
                       const location& loc,
-                      unique_ptr<module_base>&,
                       bool first,
                       bool,
-                      const variable_map& hints)
+                      module_init_extra& extra)
     {
       tracer trace ("cc::core_config_init");
       l5 ([&]{trace << "for " << rs;});
@@ -296,7 +295,7 @@ namespace build2
           h.assign ("config.bin.target") =
             cast<target_triplet> (rs["cc.target"]).string ();
 
-          if (auto l = hints["config.bin.pattern"])
+          if (auto l = extra.hints["config.bin.pattern"])
             h.assign ("config.bin.pattern") = cast<string> (l);
         }
 
@@ -342,10 +341,9 @@ namespace build2
     core_init (scope& rs,
                scope&,
                const location& loc,
-               unique_ptr<module_base>&,
                bool first,
                bool,
-               const variable_map& hints)
+               module_init_extra& extra)
     {
       tracer trace ("cc::core_init");
       l5 ([&]{trace << "for " << rs;});
@@ -356,7 +354,7 @@ namespace build2
 
       // Load cc.core.config.
       //
-      load_module (rs, rs, "cc.core.config", loc, hints);
+      load_module (rs, rs, "cc.core.config", loc, extra.hints);
 
       // Load the bin module.
       //
@@ -433,34 +431,32 @@ namespace build2
     config_init (scope& rs,
                  scope& bs,
                  const location& loc,
-                 unique_ptr<module_base>&,
                  bool,
                  bool,
-                 const variable_map& hints)
+                 module_init_extra& extra)
     {
       tracer trace ("cc::config_init");
       return init_alias (trace, rs, bs,
                          "cc.config",
                          "c.config",   "c.config.loaded",
                          "cxx.config", "cxx.config.loaded",
-                         loc, hints);
+                         loc, extra.hints);
     }
 
     bool
     init (scope& rs,
           scope& bs,
           const location& loc,
-          unique_ptr<module_base>&,
           bool,
           bool,
-          const variable_map& hints)
+          module_init_extra& extra)
     {
       tracer trace ("cc::init");
       return init_alias (trace, rs, bs,
                          "cc",
                          "c",   "c.loaded",
                          "cxx", "cxx.loaded",
-                         loc, hints);
+                         loc, extra.hints);
     }
 
     static const module_functions mod_functions[] =
diff --git a/libbuild2/cc/module.hxx b/libbuild2/cc/module.hxx
index 77fe55c..5c7b8ab 100644
--- a/libbuild2/cc/module.hxx
+++ b/libbuild2/cc/module.hxx
@@ -25,7 +25,7 @@ namespace build2
   {
     struct compiler_info;
 
-    class LIBBUILD2_CC_SYMEXPORT config_module: public module_base,
+    class LIBBUILD2_CC_SYMEXPORT config_module: public build2::module,
                                                 public virtual config_data
     {
     public:
@@ -81,7 +81,7 @@ namespace build2
       bool new_; // See guess() and init() for details.
     };
 
-    class LIBBUILD2_CC_SYMEXPORT module: public module_base,
+    class LIBBUILD2_CC_SYMEXPORT module: public build2::module,
                                          public virtual common,
                                          link_rule,
                                          compile_rule,
diff --git a/libbuild2/config/init.cxx b/libbuild2/config/init.cxx
index a7f3fc3..2f47486 100644
--- a/libbuild2/config/init.cxx
+++ b/libbuild2/config/init.cxx
@@ -30,7 +30,7 @@ namespace build2
     functions (function_map&); // functions.cxx
 
     bool
-    boot (scope& rs, const location&, unique_ptr<module_base>& mod)
+    boot (scope& rs, const location&, module_boot_extra& extra)
     {
       tracer trace ("config::boot");
 
@@ -113,17 +113,15 @@ namespace build2
         //
         vp.insert ("config.import");
 
-        unique_ptr<module> m (new module);
+        auto& m (extra.set_module (new module));
 
         // Adjust priority for the config module and import pseudo-module so
         // that their variables come first in config.build.
         //
-        m->save_module ("config", INT32_MIN);
-        m->save_module ("import", INT32_MIN);
+        m.save_module ("config", INT32_MIN);
+        m.save_module ("import", INT32_MIN);
 
-        m->save_variable (c_p, omit_null);
-
-        mod = move (m);
+        m.save_variable (c_p, omit_null);
       }
 
       // Register the config function family if this is the first instance of
@@ -149,10 +147,9 @@ namespace build2
     init (scope& rs,
           scope&,
           const location& l,
-          unique_ptr<module_base>& mod,
           bool first,
           bool,
-          const variable_map& config_hints)
+          module_init_extra& extra)
     {
       tracer trace ("config::init");
 
@@ -164,8 +161,6 @@ namespace build2
 
       l5 ([&]{trace << "for " << rs;});
 
-      assert (config_hints.empty ()); // We don't known any hints.
-
       auto& vp (rs.var_pool ());
       auto& c_l (vp.insert<paths> ("config.config.load", true /* ovr */));
       auto& c_v (vp.insert<uint64_t> ("config.version", false /*ovr*/));
@@ -266,9 +261,11 @@ namespace build2
 
       // Cache the config.config.persist value, if any.
       //
-      if (mod != nullptr)
+      if (extra.module != nullptr)
       {
-        static_cast<module&> (*mod).persist =
+        auto& m (extra.module_as<module> ());
+
+        m.persist =
           cast_null<vector<pair<string, string>>> (
             rs["config.config.persist"]);
       }
diff --git a/libbuild2/config/init.hxx b/libbuild2/config/init.hxx
index d6a1e08..d602ec9 100644
--- a/libbuild2/config/init.hxx
+++ b/libbuild2/config/init.hxx
@@ -16,18 +16,6 @@ namespace build2
 {
   namespace config
   {
-    bool
-    boot (scope&, const location&, unique_ptr<module_base>&);
-
-    bool
-    init (scope&,
-          scope&,
-          const location&,
-          unique_ptr<module_base>&,
-          bool,
-          bool,
-          const variable_map&);
-
     // Module `config` requires bootstrapping.
     //
     // `config` -- registers the configure and disfigure meta-operations,
diff --git a/libbuild2/config/module.hxx b/libbuild2/config/module.hxx
index 0a35369..297db0a 100644
--- a/libbuild2/config/module.hxx
+++ b/libbuild2/config/module.hxx
@@ -74,7 +74,7 @@ namespace build2
       }
     };
 
-    struct module: module_base
+    struct module: build2::module
     {
       config::saved_modules saved_modules;
 
diff --git a/libbuild2/cxx/init.cxx b/libbuild2/cxx/init.cxx
index cf27aaa..719a88a 100644
--- a/libbuild2/cxx/init.cxx
+++ b/libbuild2/cxx/init.cxx
@@ -353,10 +353,9 @@ namespace build2
     guess_init (scope& rs,
                 scope& bs,
                 const location& loc,
-                unique_ptr<module_base>& mod,
                 bool,
                 bool,
-                const variable_map& hints)
+                module_init_extra& extra)
     {
       tracer trace ("cxx::guess_init");
       l5 ([&]{trace << "for " << bs;});
@@ -504,10 +503,9 @@ namespace build2
       vp.insert_alias (d.c_runtime,     "cxx.runtime");
       vp.insert_alias (d.c_module_name, "cxx.module_name");
 
-      assert (mod == nullptr);
-      config_module* m (new config_module (move (d)));
-      mod.reset (m);
-      m->guess (rs, loc, hints);
+      auto& m (extra.set_module (new config_module (move (d))));
+      m.guess (rs, loc, extra.hints);
+
       return true;
     }
 
@@ -515,10 +513,9 @@ namespace build2
     config_init (scope& rs,
                  scope& bs,
                  const location& loc,
-                 unique_ptr<module_base>&,
                  bool,
                  bool,
-                 const variable_map& hints)
+                 module_init_extra& extra)
     {
       tracer trace ("cxx::config_init");
       l5 ([&]{trace << "for " << bs;});
@@ -528,11 +525,11 @@ namespace build2
       if (&rs != &bs)
         fail (loc) << "cxx.config module must be loaded in project root";
 
-      // Load cxx.guess.
+      // Load cxx.guess and share its module instance as ours.
       //
-      auto& cm (load_module<config_module> (rs, rs, "cxx.guess", loc, hints));
+      extra.module = load_module (rs, rs, "cxx.guess", loc, extra.hints);
+      extra.module_as<config_module> ().init (rs, loc, extra.hints);
 
-      cm.init (rs, loc, hints);
       return true;
     }
 
@@ -561,10 +558,9 @@ namespace build2
     init (scope& rs,
           scope& bs,
           const location& loc,
-          unique_ptr<module_base>& mod,
           bool,
           bool,
-          const variable_map& hints)
+          module_init_extra& extra)
     {
       tracer trace ("cxx::init");
       l5 ([&]{trace << "for " << bs;});
@@ -576,11 +572,8 @@ namespace build2
 
       // Load cxx.config.
       //
-      // @@ TODO: move guess to config and use return value?
-      //
-      load_module (rs, rs, "cxx.config", loc, hints);
-
-      config_module& cm (*rs.find_module<config_module> ("cxx.guess"));
+      auto& cm (
+        load_module<config_module> (rs, rs, "cxx.config", loc, extra.hints));
 
       auto& vp (rs.var_pool ());
 
@@ -630,10 +623,9 @@ namespace build2
         inc
       };
 
-      assert (mod == nullptr);
-      module* m;
-      mod.reset (m = new module (move (d)));
-      m->init (rs, loc, hints);
+      auto& m (extra.set_module (new module (move (d))));
+      m.init (rs, loc, extra.hints);
+
       return true;
     }
 
diff --git a/libbuild2/dist/init.cxx b/libbuild2/dist/init.cxx
index 93bcfdb..30cd56b 100644
--- a/libbuild2/dist/init.cxx
+++ b/libbuild2/dist/init.cxx
@@ -24,7 +24,7 @@ namespace build2
     static const rule rule_;
 
     bool
-    boot (scope& rs, const location&, unique_ptr<module_base>& mod)
+    boot (scope& rs, const location&, module_boot_extra& extra)
     {
       tracer trace ("dist::boot");
 
@@ -77,7 +77,7 @@ namespace build2
 
       // Create the module.
       //
-      mod.reset (new module (v_d_p));
+      extra.set_module (new module (v_d_p));
 
       return false;
     }
@@ -86,10 +86,9 @@ namespace build2
     init (scope& rs,
           scope&,
           const location& l,
-          unique_ptr<module_base>&,
           bool first,
           bool,
-          const variable_map& config_hints)
+          module_init_extra&)
     {
       tracer trace ("dist::init");
 
@@ -101,8 +100,6 @@ namespace build2
 
       l5 ([&]{trace << "for " << rs;});
 
-      assert (config_hints.empty ()); // We don't known any hints.
-
       // Register our wildcard rule. Do it explicitly for the alias to prevent
       // something like insert<target>(dist_id, test_id) taking precedence.
       //
diff --git a/libbuild2/dist/init.hxx b/libbuild2/dist/init.hxx
index ffaa91d..6069252 100644
--- a/libbuild2/dist/init.hxx
+++ b/libbuild2/dist/init.hxx
@@ -16,18 +16,6 @@ namespace build2
 {
   namespace dist
   {
-    bool
-    boot (scope&, const location&, unique_ptr<module_base>&);
-
-    bool
-    init (scope&,
-          scope&,
-          const location&,
-          unique_ptr<module_base>&,
-          bool,
-          bool,
-          const variable_map&);
-
     // Module `dist` requires bootstrapping.
     //
     // `dist` -- registers the dist meta-operation, registers/sets variables,
diff --git a/libbuild2/dist/module.hxx b/libbuild2/dist/module.hxx
index abc1400..983aebc 100644
--- a/libbuild2/dist/module.hxx
+++ b/libbuild2/dist/module.hxx
@@ -17,7 +17,7 @@ namespace build2
 {
   namespace dist
   {
-    struct LIBBUILD2_SYMEXPORT module: module_base
+    struct LIBBUILD2_SYMEXPORT module: build2::module
     {
       static const string name;
 
diff --git a/libbuild2/in/init.cxx b/libbuild2/in/init.cxx
index debdb45..bbf5d43 100644
--- a/libbuild2/in/init.cxx
+++ b/libbuild2/in/init.cxx
@@ -23,10 +23,9 @@ namespace build2
     base_init (scope& rs,
                scope&,
                const location&,
-               unique_ptr<module_base>&,
                bool first,
                bool,
-               const variable_map&)
+               module_init_extra&)
     {
       tracer trace ("in::base_init");
       l5 ([&]{trace << "for " << rs;});
@@ -74,10 +73,9 @@ namespace build2
     init (scope& rs,
           scope& bs,
           const location& loc,
-          unique_ptr<module_base>&,
           bool,
           bool,
-          const variable_map&)
+          module_init_extra&)
     {
       tracer trace ("in::init");
       l5 ([&]{trace << "for " << bs;});
diff --git a/libbuild2/install/init.cxx b/libbuild2/install/init.cxx
index fdcc627..5aa5b1d 100644
--- a/libbuild2/install/init.cxx
+++ b/libbuild2/install/init.cxx
@@ -129,7 +129,7 @@ namespace build2
     functions (function_map&); // functions.cxx
 
     bool
-    boot (scope& rs, const location&, unique_ptr<module_base>&)
+    boot (scope& rs, const location&, module_boot_extra&)
     {
       tracer trace ("install::boot");
       l5 ([&]{trace << "for " << rs;});
@@ -174,10 +174,9 @@ namespace build2
     init (scope& rs,
           scope& bs,
           const location& l,
-          unique_ptr<module_base>&,
           bool first,
           bool,
-          const variable_map& config_hints)
+          module_init_extra&)
     {
       tracer trace ("install::init");
 
@@ -189,8 +188,6 @@ namespace build2
 
       l5 ([&]{trace << "for " << rs;});
 
-      assert (config_hints.empty ()); // We don't known any hints.
-
       // Enter module variables.
       //
       auto& vp (rs.var_pool ());
diff --git a/libbuild2/install/init.hxx b/libbuild2/install/init.hxx
index 353b24b..5506744 100644
--- a/libbuild2/install/init.hxx
+++ b/libbuild2/install/init.hxx
@@ -16,18 +16,6 @@ namespace build2
 {
   namespace install
   {
-    bool
-    boot (scope&, const location&, unique_ptr<module_base>&);
-
-    bool
-    init (scope&,
-          scope&,
-          const location&,
-          unique_ptr<module_base>&,
-          bool,
-          bool,
-          const variable_map&);
-
     // Module `install` requires bootstrapping.
     //
     // `install` -- registers the install, uninstall, and update-for-install
diff --git a/libbuild2/module.cxx b/libbuild2/module.cxx
index cc79af0..191853a 100644
--- a/libbuild2/module.cxx
+++ b/libbuild2/module.cxx
@@ -521,7 +521,11 @@ namespace build2
 
     i = lm.emplace (mod,
                     module_state {true, false, mf.init, nullptr, loc}).first;
-    i->second.first = mf.boot (rs, loc, i->second.module);
+
+    {
+      module_boot_extra extra {i->second.module};
+      i->second.first = mf.boot (rs, loc, extra);
+    }
 
     rs.assign (rs.var_pool ().insert (mod + ".booted")) = true;
   }
@@ -608,7 +612,12 @@ namespace build2
     else
     {
       l = i != lm.end ();
-      c = l && i->second.init (rs, bs, loc, i->second.module, f, opt, hints);
+
+      if ((c = l))
+      {
+        module_init_extra extra {i->second.module, hints};
+        c = i->second.init (rs, bs, loc, f, opt, extra);
+      }
 
       lv = l;
       cv = c;
@@ -641,7 +650,7 @@ namespace build2
       init_module (rs, bs, name, loc, opt, hints);
   }
 
-  unique_ptr<module_base>&
+  const shared_ptr<module>&
   load_module (scope& rs,
                scope& bs,
                const string& name,
diff --git a/libbuild2/module.hxx b/libbuild2/module.hxx
index 00084c0..3b3dd53 100644
--- a/libbuild2/module.hxx
+++ b/libbuild2/module.hxx
@@ -22,23 +22,62 @@ namespace build2
   // A few high-level notes on the terminology: From the user's perspective,
   // the module is "loaded" (with the `using` directive). From the
   // implementation's perspectives, the module library is "loaded" and the
-  // module is "bootstrapped" (or "booted" for short) and then "initialized"
-  // (or "inited").
+  // module is optionally "bootstrapped" (or "booted" for short) and then
+  // "initialized" (or "inited").
 
-  class module_base
+  // Base class for module instance.
+  //
+  class module
   {
   public:
     virtual
-    ~module_base () = default;
+    ~module () = default;
+  };
+
+  // Module boot function signature.
+  //
+  // The module_*_extra arguments (here and in init below) are used to pass
+  // additional information that is only used by some modules. It is also a
+  // way for us to later pass more information without breaking source
+  // compatibility.
+  //
+  struct module_boot_extra
+  {
+    shared_ptr<build2::module>& module; // Module instance (out).
+
+    // Convenience functions.
+    //
+    template <typename T>
+    T& set_module (T* p) {assert (!module); module.reset (p); return *p;}
+
+    template <typename T>
+    T& module_as () {assert (module); return static_cast<T&> (*module);}
   };
 
   // Return true if the module should be initialized first (the order of
-  // initialization within each group is unspecified).
+  // initialization within the resulting two groups of modules is
+  // unspecified).
   //
   using module_boot_function =
     bool (scope& root,
           const location&,
-          unique_ptr<module_base>&);
+          module_boot_extra&);
+
+  // Module init function signature.
+  //
+  struct module_init_extra
+  {
+    shared_ptr<build2::module>& module; // Module instance (in/out).
+    const variable_map&         hints;  // Configuration hints (see below).
+
+    // Convenience functions.
+    //
+    template <typename T>
+    T& set_module (T* p) {assert (!module); module.reset (p); return *p;}
+
+    template <typename T>
+    T& module_as () {assert (module); return static_cast<T&> (*module);}
+  };
 
   // Return false if the module configuration (normally based on the default
   // values) was unsuccessful but this is not (yet) an error. One example
@@ -50,13 +89,13 @@ namespace build2
     bool (scope& root,
           scope& base,
           const location&,
-          unique_ptr<module_base>&,
           bool first,                 // First time for this project.
           bool optional,              // Loaded with using? (optional module).
-          const variable_map& hints); // Configuration hints (see below).
+          module_init_extra&);
 
   // If the boot function is not NULL, then such a module is said to require
-  // bootstrapping and must be loaded in bootstrap.build.
+  // bootstrapping and must be loaded in bootstrap.build. Such a module cannot
+  // be optional.
   //
   struct module_functions
   {
@@ -88,7 +127,7 @@ namespace build2
     bool boot;  // True if the module boot'ed but not yet init'ed.
     bool first; // True if the boot'ed module must be init'ed first.
     module_init_function* init;
-    unique_ptr<module_base> module;
+    shared_ptr<build2::module> module;
     const location loc; // Boot location.
   };
 
@@ -142,10 +181,9 @@ namespace build2
                bool optional,
                const variable_map& config_hints = empty_variable_map);
 
-  // As above but always load and return a reference to the module instance
-  // pointer (so it can be moved).
+  // As above but always load and return a pointer to the module instance.
   //
-  LIBBUILD2_SYMEXPORT unique_ptr<module_base>&
+  LIBBUILD2_SYMEXPORT const shared_ptr<module>&
   load_module (scope& root,
                scope& base,
                const string& name,
@@ -173,7 +211,7 @@ namespace build2
   // The loaded_modules map is locked per top-level (as opposed to nested)
   // context (see context.hxx for details).
   //
-  // Note: should only be constructed during context-wide serial execution.
+  // Note: should only be constructed during contexts-wide serial execution.
   //
   class LIBBUILD2_SYMEXPORT loaded_modules_lock
   {
diff --git a/libbuild2/scope.hxx b/libbuild2/scope.hxx
index dd2831c..f9dd8d9 100644
--- a/libbuild2/scope.hxx
+++ b/libbuild2/scope.hxx
@@ -399,7 +399,7 @@ namespace build2
     bool
     find_module (const string& name) const
     {
-      return root_extra->modules.find_module<module_base> (name) != nullptr;
+      return root_extra->modules.find_module<module> (name) != nullptr;
     }
 
     template <typename T>
diff --git a/libbuild2/test/init.cxx b/libbuild2/test/init.cxx
index 6a13990..ec95927 100644
--- a/libbuild2/test/init.cxx
+++ b/libbuild2/test/init.cxx
@@ -25,7 +25,7 @@ namespace build2
   namespace test
   {
     bool
-    boot (scope& rs, const location&, unique_ptr<module_base>& mod)
+    boot (scope& rs, const location&, module_boot_extra& extra)
     {
       tracer trace ("test::boot");
 
@@ -116,7 +116,8 @@ namespace build2
           v = cast<target_triplet> (rs.ctx.global_scope["build.host"]);
       }
 
-      mod.reset (new module (move (d)));
+      extra.set_module (new module (move (d)));
+
       return false;
     }
 
@@ -124,10 +125,9 @@ namespace build2
     init (scope& rs,
           scope&,
           const location& l,
-          unique_ptr<module_base>& mod,
           bool first,
           bool,
-          const variable_map& config_hints)
+          module_init_extra& extra)
     {
       tracer trace ("test::init");
 
@@ -139,12 +139,10 @@ namespace build2
 
       l5 ([&]{trace << "for " << rs;});
 
-      assert (mod != nullptr);
-      module& m (static_cast<module&> (*mod));
+      auto& m (extra.module_as<module> ());
 
       // Configure.
       //
-      assert (config_hints.empty ()); // We don't known any hints.
 
       // Adjust module priority so that the config.test.* values are saved at
       // the end of config.build.
diff --git a/libbuild2/test/init.hxx b/libbuild2/test/init.hxx
index 49cdb14..7683858 100644
--- a/libbuild2/test/init.hxx
+++ b/libbuild2/test/init.hxx
@@ -16,18 +16,6 @@ namespace build2
 {
   namespace test
   {
-    bool
-    boot (scope&, const location&, unique_ptr<module_base>&);
-
-    bool
-    init (scope&,
-          scope&,
-          const location&,
-          unique_ptr<module_base>&,
-          bool,
-          bool,
-          const variable_map&);
-
     // Module `test` requires bootstrapping.
     //
     // `test` -- registers the test and update-for-test operations, registers/
diff --git a/libbuild2/test/module.hxx b/libbuild2/test/module.hxx
index 584cb84..af06434 100644
--- a/libbuild2/test/module.hxx
+++ b/libbuild2/test/module.hxx
@@ -17,7 +17,10 @@ namespace build2
 {
   namespace test
   {
-    struct module: module_base, virtual common, default_rule, group_rule
+    struct module: build2::module,
+                   virtual common,
+                   default_rule,
+                   group_rule
     {
       const test::group_rule&
       group_rule () const
diff --git a/libbuild2/version/init.cxx b/libbuild2/version/init.cxx
index f69e416..d07198c 100644
--- a/libbuild2/version/init.cxx
+++ b/libbuild2/version/init.cxx
@@ -32,7 +32,7 @@ namespace build2
     static const manifest_install_rule manifest_install_rule_;
 
     bool
-    boot (scope& rs, const location& l, unique_ptr<module_base>& mod)
+    boot (scope& rs, const location& l, module_boot_extra& extra)
     {
       tracer trace ("version::boot");
       l5 ([&]{trace << "for " << rs;});
@@ -271,13 +271,14 @@ namespace build2
 
       set ("version.revision", uint64_t (v.revision));
 
-      // Create the module.
+      // Create the module instance.
       //
-      mod.reset (new module (cast<project_name> (rs.vars[ctx.var_project]),
-                             move (v),
-                             committed,
-                             rewritten,
-                             move (ds)));
+      extra.set_module (
+        new module (cast<project_name> (rs.vars[ctx.var_project]),
+                    move (v),
+                    committed,
+                    rewritten,
+                    move (ds)));
 
       return true; // Init first (dist.package, etc).
     }
@@ -289,10 +290,9 @@ namespace build2
     init (scope& rs,
           scope&,
           const location& l,
-          unique_ptr<module_base>& mod,
           bool first,
           bool,
-          const variable_map&)
+          module_init_extra& extra)
     {
       tracer trace ("version::init");
 
@@ -305,7 +305,7 @@ namespace build2
       //
       load_module (rs, rs, "in.base", l);
 
-      module& m (static_cast<module&> (*mod));
+      auto& m (extra.module_as<module> ());
       const standard_version& v (m.version);
 
       // If the dist module is used, set its dist.package and register the
diff --git a/libbuild2/version/module.hxx b/libbuild2/version/module.hxx
index 174da7b..4d51d4e 100644
--- a/libbuild2/version/module.hxx
+++ b/libbuild2/version/module.hxx
@@ -29,7 +29,7 @@ namespace build2
 
     using dependencies = std::map<string, dependency>;
 
-    struct module: module_base
+    struct module: build2::module
     {
       using dependencies_type = version::dependencies;