Support private values 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 <iostream>
 
 #include "base/environment.h"
 #include "base/strings/string_util.h"
@@ skipping 43 matching lines @@
                           Err* err) {
   if (!block) {
     FillNeedsBlockError(function, err);
     return false;
   }
 
   // Copy the target defaults, if any, into the scope we're going to execute
   // the block in.
   const Scope* default_scope = scope->GetTargetDefaults(target_type);
   if (default_scope) {
-    if (!default_scope->NonRecursiveMergeTo(block_scope, false, function,
-                                            "target defaults", err))
+    Scope::MergeOptions merge_options;
+    merge_options.skip_private_vars = true;
+    if (!default_scope->NonRecursiveMergeTo(block_scope, merge_options,
+                                            function, "target defaults", err))
       return false;
   }
 
   // The name is the single argument to the target function.
   if (!EnsureSingleStringArg(function, args, err))
     return false;
 
   // Set the target name variable to the current target, and mark it used
   // because we don't want to issue an error if the script ignores it.
   const base::StringPiece target_name("target_name");
@@ skipping 363 matching lines @@
     "  Note that you can not import a BUILD.gn file that's otherwise used\n"
     "  in the build. Files must either be imported or implicitly loaded as\n"
     "  a result of deps rules, but not both.\n"
     "\n"
     "  The imported file's scope will be merged with the scope at the point\n"
     "  import was called. If there is a conflict (both the current scope and\n"
     "  the imported file define some variable or rule with the same name but\n"
     "  different value), a runtime error will be thrown. Therefore, it's good\n"
     "  practice to minimize the stuff that an imported file defines.\n"
     "\n"
+    "  Variables and templates beginning with an underscore '_' are\n"
+    "  considered private and will not be imported. Imported files can use\n"
+    "  such variables for internal computation without affecting other files.\n"
+    "\n"
     "Examples:\n"
     "\n"
     "  import(\"//build/rules/idl_compilation_rule.gni\")\n"
     "\n"
     "  # Looks in the current directory.\n"
     "  import(\"my_vars.gni\")\n";
 
 Value RunImport(Scope* scope,
                 const FunctionCallNode* function,
                 const std::vector<Value>& args,
@@ skipping 276 matching lines @@
     return found_function->second.executed_block_runner(
         function, args.list_value(), &block_scope, err);
   }
 
   // Otherwise it's a no-block function.
   return found_function->second.no_block_runner(scope, function,
                                                 args.list_value(), err);
 }
 
 }  // namespace functions