tools/gn: provide better error message for bogus binary expressions

tools/gn/parser_unittest.cc

 // Copyright (c) 2013 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.
 
 #include <iostream>
 #include <sstream>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/input_file.h"
 #include "tools/gn/parser.h"
@@ skipping 186 matching lines @@
       "   LITERAL(2)\n"
       "   LITERAL(3)\n"
       "  IDENTIFIER(foo)\n");
   DoExpressionPrintTest("[1,\n2,\n 3,\n  4]",
       "LIST\n"
       " LITERAL(1)\n"
       " LITERAL(2)\n"
       " LITERAL(3)\n"
       " LITERAL(4)\n");
 
-  DoExpressionErrorTest("[a, 2+,]", 1, 6);
+  DoExpressionErrorTest("[a, 2+,]", 1, 7);

[mdempsky, 2015/04/06 23:41:51]

This expectation change is because GN used to give an error like:

    ERROR at //BUILD.gn:6:6: Expected right hand side for '+'
    [a, 2+,]
         ^

but now it instead says:

    ERROR at //BUILD.gn:6:7: Unexpected token ','
    [a, 2+,]
          ^

As mentioned in the bug, this is arguably a worse error message, but it seems to
be in-line with what C++ developers should be accustomed to from compiler error
messages for invalid input like this.

   DoExpressionErrorTest("[,]", 1, 2);
   DoExpressionErrorTest("[a,,]", 1, 4);
 }
 
 TEST(Parser, Assignment) {
   DoParserPrintTest("a=2",
                     "BLOCK\n"
                     " BINARY(=)\n"
                     "  IDENTIFIER(a)\n"
                     "  LITERAL(2)\n");
@@ skipping 18 matching lines @@
                     "BLOCK\n"
                     " BINARY(=)\n"
                     "  IDENTIFIER(a)\n"
                     "  BINARY(+)\n"
                     "   ACCESSOR\n"
                     "    b\n"
                     "    IDENTIFIER(c)\n"
                     "   LITERAL(2)\n");
   DoParserErrorTest("a = b.c.d", 1, 6);  // Can't nest accessors (currently).
   DoParserErrorTest("a.b = 5", 1, 1);  // Can't assign to accessors (currently).
+
+  // Error at the bad dot in the RHS, not the + operator (crbug.com/472038).
+  DoParserErrorTest("foo(a + b.c.d)", 1, 10);
 }
 
 TEST(Parser, Condition) {
   DoParserPrintTest("if(1) { a = 2 }",
                     "BLOCK\n"
                     " CONDITION\n"
                     "  LITERAL(1)\n"
                     "  BLOCK\n"
                     "   BINARY(=)\n"
                     "    IDENTIFIER(a)\n"
@@ skipping 438 matching lines @@
 // freestanding block.
 TEST(Parser, StandaloneBlock) {
   DoParserErrorTest(
       "if (true) {\n"
       "}\n"
       "{\n"
       "  assert(false)\n"
       "}\n",
       3, 1);
 }