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