[feaLib] Clarify error message for malformed glyph class references

The new message makes clearer what exactly the parser was looking for
when processing a glyph class reference.

Lib/fontTools/feaLib/parser.py

@@ -92,8 +92,10 @@ class Parser(object):
                         self.cur_token_location_)
                 result.update(gc.glyphs)
             else:
-                raise ParserError("Expected glyph name, range, or reference",
-                                  self.cur_token_location_)
+                raise ParserError(
+                    "Expected glyph name, glyph range, "
+                    "or glyph class reference",
+                    self.cur_token_location_)
         self.expect_symbol_("]")
         return result
 

Lib/fontTools/feaLib/parser_test.py

@@ -26,7 +26,8 @@ class ParserTest(unittest.TestCase):
 
     def test_glyphclass_bad(self):
         self.assertRaisesRegex(
-            ParserError, "Expected glyph name, range, or reference",
+            ParserError,
+            "Expected glyph name, glyph range, or glyph class reference",
             self.parse, "@bad = [a 123];")
 
     def test_glyphclass_duplicate(self):