tools/gn/function_set_defaults.cc

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "tools/gn/err.h"
   6 #include "tools/gn/functions.h"
   7 #include "tools/gn/parse_tree.h"
   8 #include "tools/gn/scope.h"
   9
  10 namespace functions {
  11
  12 const char kSetDefaults[] = "set_defaults";
  13 const char kSetDefaults_HelpShort[] =
  14     "set_defaults: Set default values for a target type.";
  15 const char kSetDefaults_Help[] =
  16     "set_defaults: Set default values for a target type.\n"
  17     "\n"
  18     "  set_defaults(<target_type_name>) { <values...> }\n"
  19     "\n"
  20     "  Sets the default values for a given target type. Whenever\n"
  21     "  target_type_name is seen in the future, the values specified in\n"
  22     "  set_default's block will be copied into the current scope.\n"
  23     "\n"
  24     "  When the target type is used, the variable copying is very strict.\n"
  25     "  If a variable with that name is already in scope, the build will fail\n"
  26     "  with an error.\n"
  27     "\n"
  28     "  set_defaults can be used for built-in target types (\"executable\",\n"
  29     "  \"shared_library\", etc.) and custom ones defined via the \"template\"\n"
  30     "  command.\n"
  31     "\n"
  32     "Example:\n"
  33     "  set_defaults(\"static_library\") {\n"
  34     "    configs = [ \"//tools/mything:settings\" ]\n"
  35     "  }\n"
  36     "\n"
  37     "  static_library(\"mylib\")\n"
  38     "    # The configs will be auto-populated as above. You can remove it if\n"
  39     "    # you don't want the default for a particular default:\n"
  40     "    configs -= \"//tools/mything:settings\"\n"
  41     "  }\n";
  42
  43 Value RunSetDefaults(Scope* scope,
  44                      const FunctionCallNode* function,
  45                      const std::vector<Value>& args,
  46                      BlockNode* block,
  47                      Err* err) {
  48   if (!EnsureSingleStringArg(function, args, err))
  49     return Value();
  50   const std::string& target_type(args[0].string_value());
  51
  52   // Ensure there aren't defaults already set.
  53   //
  54   // It might be nice to allow multiple calls set mutate the defaults. The
  55   // main case for this is where some local portions of the code want
  56   // additional defaults they specify in an imported file.
  57   //
  58   // Currently, we don't allow imports to clobber anything, so this wouldn't
  59   // work. Additionally, allowing this would be undesirable since we don't
  60   // want multiple imports to each try to set defaults, since it might look
  61   // like the defaults are modified by each one in sequence, while in fact
  62   // imports would always clobber previous values and it would be confusing.
  63   //
  64   // If we wanted this, the solution would be to allow imports to overwrite
  65   // target defaults set up by the default build config only. That way there
  66   // are no ordering issues, but this would be more work.
  67   if (scope->GetTargetDefaults(target_type)) {
  68     *err = Err(function->function(),
  69                "This target type defaults were already set.");
  70     return Value();
  71   }
  72
  73   if (!block) {
  74     FillNeedsBlockError(function, err);
  75     return Value();
  76   }
  77
  78   // Run the block for the rule invocation.
  79   Scope block_scope(scope);
  80   block->Execute(&block_scope, err);
  81   if (err->has_error())
  82     return Value();
  83
  84   // Now copy the values set on the scope we made into the free-floating one
  85   // (with no containing scope) used to hold the target defaults.
  86   Scope* dest = scope->MakeTargetDefaults(target_type);
  87   block_scope.NonRecursiveMergeTo(dest, Scope::MergeOptions(), function,
  88                                   "<SHOULD NOT FAIL>", err);
  89   return Value();
  90 }
  91
  92 }  // namespace functions