Add support for default extension specification, trailing dot escaping

For example:

cxx{*}: extension = cxx

cxx{foo}         # foo.cxx
cxx{foo.test}    # foo.test      (probably what we want...)
cxx{foo.test...} # foo.test.cxx  (... is this)
cxx{foo..}       # foo.
cxx{foo....}     # foo..
cxx{foo.....}    # error (must come in escape pair)

1 files changed, 3 insertions, 5 deletions

diff --git a/build2/cc/common.cxx b/build2/cc/common.cxx
index ca73483..c6ef3bd 100644
--- a/build2/cc/common.cxx
+++ b/build2/cc/common.cxx
@@ -431,11 +431,9 @@ namespace build2
       {
         // This is import.
         //
-        optional<string> ext;
-
-        // Changes name.
-        //
-        const target_type* tt (s.find_target_type (n, ext, location ()));
+        auto rp (s.find_target_type (n, location ())); // Note: changes name.
+        const target_type* tt (rp.first);
+        optional<string>& ext (rp.second);
 
         if (tt == nullptr)
           fail << "unknown target type '" << n.type << "' in library " << n;