Allow creation and modification of scopes in GN.

tools/gn/functions.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 "tools/gn/functions.h"
 
 #include <stddef.h>
 #include <iostream>
 #include <utility>
 
@@ skipping 594 matching lines @@
 // set_sources_assignment_filter -----------------------------------------------
 
 const char kSetSourcesAssignmentFilter[] = "set_sources_assignment_filter";
 const char kSetSourcesAssignmentFilter_HelpShort[] =
     "set_sources_assignment_filter: Set a pattern to filter source files.";
 const char kSetSourcesAssignmentFilter_Help[] =
     "set_sources_assignment_filter: Set a pattern to filter source files.\n"
     "\n"
     "  The sources assignment filter is a list of patterns that remove files\n"
     "  from the list implicitly whenever the \"sources\" variable is\n"
-    "  assigned to. This is intended to be used to globally filter out files\n"
-    "  with platform-specific naming schemes when they don't apply, for\n"
-    "  example, you may want to filter out all \"*_win.cc\" files on non-\n"
-    "  Windows platforms.\n"
+    "  assigned to. This will do nothing for non-lists.\n"
+    "\n"
+    "  This is intended to be used to globally filter out files with\n"
+    "  platform-specific naming schemes when they don't apply, for example\n"
+    "  you may want to filter out all \"*_win.cc\" files on non-Windows\n"
+    "  platforms.\n"
     "\n"
     "  Typically this will be called once in the master build config script\n"
     "  to set up the filter for the current platform. Subsequent calls will\n"
     "  overwrite the previous values.\n"
     "\n"
     "  If you want to bypass the filter and add a file even if it might\n"
     "  be filtered out, call set_sources_assignment_filter([]) to clear the\n"
     "  list of filters. This will apply until the current scope exits\n"
     "\n"
     "How to use patterns\n"
@@ skipping 469 matching lines @@
   }
 
   // Otherwise it's a no-block function.
   if (!VerifyNoBlockForFunctionCall(function, block, err))
     return Value();
   return found_function->second.no_block_runner(scope, function,
                                                 args.list_value(), err);
 }
 
 }  // namespace functions