Match rule to libul{} with explicit bin.metadata hint

This rule picks, matches, and unmatches (if possible) a member for the
purpose of making its metadata (for example, library's poptions, if
it's one of the cc libraries) available.

1 files changed, 20 insertions, 6 deletions

diff --git a/libbuild2/bin/rule.hxx b/libbuild2/bin/rule.hxx
index 8bc30c7..fcbd0ca 100644
--- a/libbuild2/bin/rule.hxx
+++ b/libbuild2/bin/rule.hxx
@@ -30,19 +30,33 @@ namespace build2
       apply (action, target&) const override;
     };
 
-    // "Fail rule" for libul{} that issues diagnostics if someone tries to
-    // build this group directly.
+    // If metadata is false, the this is a "fail rule" for libul{} that issues
+    // diagnostics if someone tries to build this group directly.
     //
-    class libul_rule: public simple_rule
+    // If metadata is true, then this rule only matches with the explicit
+    // `bin.metadata` hint. In this case it picks, matches, and unmatches (if
+    // possible) a member for the purpose of making its metadata (for example,
+    // library's poptions, if it's one of the cc libraries) available.
+    //
+    // The underlying idea here is that someone else (e.g., cc::link_rule)
+    // makes a more informed choice and we piggy back on that decision,
+    // falling back to making our own based on bin.lib and bin.exe.lib. Note
+    // that for update this rule always returns target_state::unchanged.
+    //
+    class libul_rule: public rule
     {
     public:
-      libul_rule () {}
+      explicit
+      libul_rule (bool md): metadata_ (md) {}
 
       virtual bool
-      match (action, target&) const override;
+      match (action, target&, const string&, match_extra&) const override;
 
       virtual recipe
-      apply (action, target&) const override;
+      apply (action, target&, match_extra&) const override;
+
+    private:
+      bool metadata_;
     };
 
     // Pass-through to group members rule, similar to alias.