Mojo: Mojom: Disallow trailing commas in parameter lists.

mojo/public/tools/bindings/pylib/mojom/parse/parser.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Generates a syntax tree from a Mojo IDL file."""
 
 import imp
 import os.path
 import sys
 
@@ skipping 159 matching lines @@
   def p_response(self, p):
     """response : RESPONSE LPAREN parameter_list RPAREN
                 | """
     if len(p) > 3:
       p[0] = p[3]
 
   def p_method(self, p):
     """method : NAME ordinal LPAREN parameter_list RPAREN response SEMI"""
     p[0] = ('METHOD', p[1], p[4], p[2], p[6])
 
-  def p_parameter_list(self, p):
-    """parameter_list : parameter
-                      | parameter COMMA parameter_list
-                      | """
-    if len(p) == 1:
-      p[0] = []
-    elif len(p) == 2:
-      p[0] = [p[1]]
-    else:
-      p[0] = [p[1]] + p[3]
+  def p_parameter_list_1(self, p):

[jamesr, 2014/07/02 22:03:01]

do _1 / _2 have any particular meaning? i'd expect naively for this to mean
"with one parameter" and "with two parameters" but that clearly isn't the case.
can we name these something else?

+    """parameter_list : """
+    p[0] = []
+
+  def p_parameter_list_2(self, p):
+    """parameter_list : nonempty_parameter_list"""
+    p[0] = p[1]
+
+  def p_nonempty_parameter_list_1(self, p):
+    """nonempty_parameter_list : parameter"""
+    p[0] = [p[1]]
+
+  def p_nonempty_parameter_list_2(self, p):
+    """nonempty_parameter_list : nonempty_parameter_list COMMA parameter"""
+    p[0] = p[1]
+    p[0].append(p[3])
 
   def p_parameter(self, p):
     """parameter : typename NAME ordinal"""
     p[0] = ast.Parameter(p[1], p[2], p[3],
                          filename=self.filename, lineno=p.lineno(1))
 
   def p_typename(self, p):
     """typename : basictypename
                 | array
                 | fixed_array
@@ skipping 126 matching lines @@
 
 def Parse(source, filename):
   lexer = Lexer(filename)
   parser = Parser(lexer, source, filename)
 
   lex.lex(object=lexer)
   yacc.yacc(module=parser, debug=0, write_tables=0)
 
   tree = yacc.parse(source)
   return tree