Add support for rule hints

A rule hint is a target attribute, for example:

[rule_hint=cxx] exe{hello}: c{hello}

Rule hints can be used to resolve ambiguity when multiple rules match the same
target as well as to override an unambiguous match.

6 files changed, 39 insertions, 38 deletions

diff --git a/libbuild2/bin/def-rule.cxx b/libbuild2/bin/def-rule.cxx
index 63508c5..c0e82fb 100644
--- a/libbuild2/bin/def-rule.cxx
+++ b/libbuild2/bin/def-rule.cxx
@@ -449,7 +449,7 @@ namespace build2
     }
 
     bool def_rule::
-    match (action a, target& t, const string&) const
+    match (action a, target& t) const
     {
       tracer trace ("bin::def_rule::match");
 
diff --git a/libbuild2/bin/def-rule.hxx b/libbuild2/bin/def-rule.hxx
index 32423a0..acdf841 100644
--- a/libbuild2/bin/def-rule.hxx
+++ b/libbuild2/bin/def-rule.hxx
@@ -24,7 +24,7 @@ namespace build2
       def_rule () {}
 
       virtual bool
-      match (action, target&, const string&) const override;
+      match (action, target&) const override;
 
       virtual recipe
       apply (action, target&) const override;
diff --git a/libbuild2/bin/init.cxx b/libbuild2/bin/init.cxx
index ab3980a..2b1df97 100644
--- a/libbuild2/bin/init.cxx
+++ b/libbuild2/bin/init.cxx
@@ -547,7 +547,7 @@ namespace build2
                 &target_pattern_fix<wasm_ext>,
                 &target_print_0_ext_verb, // Fixed extension, no use printing.
                 &file_search,
-                false /* see_through */}));
+                target_type::flag::none}));
 
           if (install_loaded)
           {
@@ -578,8 +578,6 @@ namespace build2
 
         // Similar to alias.
         //
-
-        //@@ outer
         r.insert<lib> (perform_id,   0, "bin.lib", lib_);
         r.insert<lib> (configure_id, 0, "bin.lib", lib_);
 
@@ -927,7 +925,7 @@ namespace build2
               &target_pattern_fix<pdb_ext>,
               &target_print_0_ext_verb, // Fixed extension, no use printing.
               &file_search,
-              false /* see_through */}));
+              target_type::flag::none}));
 
         if (cast_false<bool> (rs["install.loaded"]))
         {
diff --git a/libbuild2/bin/rule.cxx b/libbuild2/bin/rule.cxx
index 021a768..85cc9de 100644
--- a/libbuild2/bin/rule.cxx
+++ b/libbuild2/bin/rule.cxx
@@ -20,7 +20,7 @@ namespace build2
     // obj_rule
     //
     bool obj_rule::
-    match (action a, target& t, const string&) const
+    match (action a, target& t) const
     {
       const char* n (t.dynamic_type ().name); // Ignore derived type.
 
@@ -35,7 +35,7 @@ namespace build2
     // libul_rule
     //
     bool libul_rule::
-    match (action a, target& t, const string&) const
+    match (action a, target& t) const
     {
       fail << diag_doing (a, t) << " target group" <<
         info << "explicitly select libua{} or libus{} member" << endf;
@@ -50,7 +50,7 @@ namespace build2
     // our prerequisites.
     //
     bool lib_rule::
-    match (action a, target& xt, const string&) const
+    match (action a, target& xt) const
     {
       lib& t (xt.as<lib> ());
 
diff --git a/libbuild2/bin/rule.hxx b/libbuild2/bin/rule.hxx
index ffb975d..8bc30c7 100644
--- a/libbuild2/bin/rule.hxx
+++ b/libbuild2/bin/rule.hxx
@@ -24,7 +24,7 @@ namespace build2
       obj_rule () {}
 
       virtual bool
-      match (action, target&, const string&) const override;
+      match (action, target&) const override;
 
       virtual recipe
       apply (action, target&) const override;
@@ -39,7 +39,7 @@ namespace build2
       libul_rule () {}
 
       virtual bool
-      match (action, target&, const string&) const override;
+      match (action, target&) const override;
 
       virtual recipe
       apply (action, target&) const override;
@@ -53,7 +53,7 @@ namespace build2
       lib_rule () {}
 
       virtual bool
-      match (action, target&, const string&) const override;
+      match (action, target&) const override;
 
       virtual recipe
       apply (action, target&) const override;
diff --git a/libbuild2/bin/target.cxx b/libbuild2/bin/target.cxx
index bf701c9..a8d015b 100644
--- a/libbuild2/bin/target.cxx
+++ b/libbuild2/bin/target.cxx
@@ -21,7 +21,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::none
     };
 
     const target_type bmix::static_type
@@ -34,7 +34,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::none
     };
 
     const target_type hbmix::static_type
@@ -47,7 +47,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::none
     };
 
     const target_type libx::static_type
@@ -60,7 +60,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::member_hint, // Use untyped hint for group members.
     };
 
     const target_type libux::static_type
@@ -73,7 +73,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::none
     };
 
     // Note that we link groups during the load phase since this is often
@@ -108,7 +108,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type bmie::static_type
@@ -121,7 +121,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type hbmie::static_type
@@ -134,7 +134,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type obja::static_type
@@ -147,7 +147,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type bmia::static_type
@@ -160,7 +160,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type hbmia::static_type
@@ -173,7 +173,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type objs::static_type
@@ -186,7 +186,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type bmis::static_type
@@ -199,7 +199,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type hbmis::static_type
@@ -212,7 +212,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type libue::static_type
@@ -225,7 +225,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type libua::static_type
@@ -238,7 +238,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     const target_type libus::static_type
@@ -251,7 +251,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
-      false
+      target_type::flag::none
     };
 
     // obj{}, [h]bmi{}, and libu{} group factory.
@@ -292,7 +292,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::member_hint, // Use untyped hint for group members.
     };
 
     const target_type bmi::static_type
@@ -305,7 +305,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::member_hint, // Use untyped hint for group members.
     };
 
     const target_type hbmi::static_type
@@ -318,7 +318,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::member_hint, // Use untyped hint for group members.
     };
 
     // The same as g_factory() but without E.
@@ -352,7 +352,7 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false
+      target_type::flag::member_hint, // Use untyped hint for group members.
     };
 
     // What extensions should we use? At the outset, this is platform-
@@ -375,7 +375,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &file_search,
-      false
+      target_type::flag::none
     };
 
     const target_type libs::static_type
@@ -388,7 +388,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &file_search,
-      false
+      target_type::flag::none
     };
 
     // lib
@@ -435,7 +435,10 @@ namespace build2
       nullptr,
       nullptr,
       &target_search,
-      false // Note: not see-through ("alternatives" group).
+
+      // Note: not see-through ("alternatives" group).
+      //
+      target_type::flag::member_hint, // Use untyped hint for group members.
     };
 
     // libi
@@ -450,7 +453,7 @@ namespace build2
       &target_pattern_var<nullptr>,
       nullptr,
       &file_search,
-      false
+      target_type::flag::none
     };
 
     // def
@@ -467,7 +470,7 @@ namespace build2
       &target_pattern_fix<def_ext>,
       nullptr,
       &file_search,
-      false
+      target_type::flag::none
     };
   }
 }