Tighten up attribute recognition during parsing

Now it should be possible to use `[]` for wildcard patterns, for example:

  foo = foo.[hit]xx

Note that a leading bracket expression will still be recognized as attributes
and escaping or quoting it will inhibit pattern matching. To resolve this case
we need to specify an empty attribute list:

  foo = [] [abc]-foo.cxx

1 files changed, 9 insertions, 2 deletions

diff --git a/libbuild2/parser.hxx b/libbuild2/parser.hxx
index d82496d..b07936c 100644
--- a/libbuild2/parser.hxx
+++ b/libbuild2/parser.hxx
@@ -535,8 +535,8 @@ namespace build2
         lexer_->mode (m, ps);
       else
         // As a sanity check, make sure the mode matches the next token. Note
-        // that we don't check the pair separator since it can be overriden by
-        // the lexer's mode() implementation.
+        // that we don't check the attributes flags or the pair separator
+        // since they can be overridden by the lexer's mode() implementation.
         //
         assert (replay_i_ != replay_data_.size () &&
                 replay_data_[replay_i_].mode == m);
@@ -555,6 +555,13 @@ namespace build2
     }
 
     void
+    enable_attributes ()
+    {
+      if (replay_ != replay::play)
+        lexer_->enable_attributes ();
+    }
+
+    void
     expire_mode ()
     {
       if (replay_ != replay::play)