tools/gn/function_set_defaults.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/err.h"
#include "tools/gn/functions.h"
#include "tools/gn/parse_tree.h"
#include "tools/gn/scope.h"

namespace functions {

const char kSetDefaults[] = "set_defaults";
const char kSetDefaults_HelpShort[] =
    "set_defaults: Set default values for a target type.";
const char kSetDefaults_Help[] =
    "set_defaults: Set default values for a target type.\n"
    "\n"
    "  set_defaults(<target_type_name>) { <values...> }\n"
    "\n"
    "  Sets the default values for a given target type. Whenever\n"
    "  target_type_name is seen in the future, the values specified in\n"
    "  set_default's block will be copied into the current scope.\n"
    "\n"
    "  When the target type is used, the variable copying is very strict.\n"
    "  If a variable with that name is already in scope, the build will fail\n"
    "  with an error.\n"
    "\n"
    "  set_defaults can be used for built-in target types (\"executable\",\n"
    "  \"shared_library\", etc.) and custom ones defined via the \"template\"\n"
    "  command.\n"
    "\n"
    "Example:\n"
    "  set_defaults(\"static_library\") {\n"
    "    configs = [ \"//tools/mything:settings\" ]\n"
    "  }\n"
    "\n"
    "  static_library(\"mylib\")\n"
    "    # The configs will be auto-populated as above. You can remove it if\n"
    "    # you don't want the default for a particular default:\n"
    "    configs -= \"//tools/mything:settings\"\n"
    "  }\n";

Value RunSetDefaults(Scope* scope,
                     const FunctionCallNode* function,
                     const std::vector<Value>& args,
                     BlockNode* block,
                     Err* err) {
  if (!EnsureSingleStringArg(function, args, err))
    return Value();
  const std::string& target_type(args[0].string_value());

  // Ensure there aren't defaults already set.
  //
  // It might be nice to allow multiple calls set mutate the defaults. The
  // main case for this is where some local portions of the code want
  // additional defaults they specify in an imported file.
  //
  // Currently, we don't allow imports to clobber anything, so this wouldn't
  // work. Additionally, allowing this would be undesirable since we don't
  // want multiple imports to each try to set defaults, since it might look
  // like the defaults are modified by each one in sequence, while in fact
  // imports would always clobber previous values and it would be confusing.
  //
  // If we wanted this, the solution would be to allow imports to overwrite
  // target defaults set up by the default build config only. That way there
  // are no ordering issues, but this would be more work.
  if (scope->GetTargetDefaults(target_type)) {
    *err = Err(function->function(),
               "This target type defaults were already set.");
    return Value();
  }

  if (!block) {
    FillNeedsBlockError(function, err);
    return Value();
  }

  // Run the block for the rule invocation.
  Scope block_scope(scope);
  block->ExecuteBlockInScope(&block_scope, err);
  if (err->has_error())
    return Value();

  // Now copy the values set on the scope we made into the free-floating one
  // (with no containing scope) used to hold the target defaults.
  Scope* dest = scope->MakeTargetDefaults(target_type);
  block_scope.NonRecursiveMergeTo(dest, Scope::MergeOptions(), function,
                                  "<SHOULD NOT FAIL>", err);
  return Value();
}

}  // namespace functions