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, 22 insertions, 29 deletions

diff --git a/build2/target.txx b/build2/target.txx
index d832d6b..8030c1a 100644
--- a/build2/target.txx
+++ b/build2/target.txx
@@ -55,29 +55,27 @@ namespace build2
 
   template <const char* ext>
   bool
-  target_pattern_fix (const target_type&, const scope&, string& v, bool r)
+  target_pattern_fix (const target_type&,
+                      const scope&,
+                      string&,
+                      optional<string>& e,
+                      bool r)
   {
-    size_t p (path::traits::find_extension (v));
-
     if (r)
     {
       // If we get called to reverse then it means we've added the extension
-      // in the first place. So simply strip it.
+      // in the first place.
       //
-      assert (p != string::npos);
-      v.resize (p);
+      assert (e);
+      e = nullopt;
     }
     //
     // We only add our extension if there isn't one already.
     //
-    else if (p == string::npos)
+    else if (!e)
     {
-      if (*ext != '\0') // Don't add empty extension (means no extension).
-      {
-        v += '.';
-        v += ext;
-        return true;
-      }
+      e = ext;
+      return true;
     }
 
     return false;
@@ -115,35 +113,30 @@ namespace build2
 
   template <const char* var, const char* def>
   bool
-  target_pattern_var (const target_type& tt, const scope& s, string& v, bool r)
+  target_pattern_var (const target_type& tt,
+                      const scope& s,
+                      string&,
+                      optional<string>& e,
+                      bool r)
   {
-    size_t p (path::traits::find_extension (v));
-
     if (r)
     {
       // If we get called to reverse then it means we've added the extension
-      // in the first place. So simply strip it.
+      // in the first place.
       //
-      assert (p != string::npos);
-      v.resize (p);
+      assert (e);
+      e = nullopt;
     }
     //
     // We only add our extension if there isn't one already.
     //
-    else if (p == string::npos)
+    else if (!e)
     {
       // Use empty name as a target since we only want target type/pattern-
       // specific variables that match any target (e.g., '*' but not '*.txt').
       //
-      if (auto e = target_extension_var_impl (tt, string (), s, var, def))
-      {
-        if (!e->empty ()) // Don't add empty extension (means no extension).
-        {
-          v += '.';
-          v += *e;
-          return true;
-        }
-      }
+      if ((e = target_extension_var_impl (tt, string (), s, var, def)))
+        return true;
     }
 
     return false;