blob: 7af688e75b2344c3b1039d231e13c9f2249169c1 [file] [log] [blame]
// 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 "tools/gn/parse_tree.h"
#include "tools/gn/scope.h"
#include "tools/gn/template.h"
#include "tools/gn/value.h"
namespace functions {
const char kTemplate[] = "template";
const char kTemplate_HelpShort[] =
"template: Define a template rule.";
const char kTemplate_Help[] =
"template: Define a template rule.\n"
" A template defines a custom name that acts like a function. It\n"
" provides a way to add to the built-in target types.\n"
" The template() function is used to declare a template. To invoke the\n"
" template, just use the name of the template like any other target\n"
" type.\n"
" Often you will want to declare your template in a special file that\n"
" other files will import (see \"gn help import\") so your template\n"
" rule can be shared across build files.\n"
"More details:\n"
" When you call template() it creates a closure around all variables\n"
" currently in scope with the code in the template block. When the\n"
" template is invoked, the closure will be executed.\n"
" When the template is invoked, the code in the caller is executed and\n"
" passed to the template code as an implicit \"invoker\" variable. The\n"
" template uses this to read state out of the invoking code.\n"
" One thing explicitly excluded from the closure is the \"current\n"
" directory\" against which relative file names are resolved. The\n"
" current directory will be that of the invoking code, since typically\n"
" that code specifies the file names. This means all files internal\n"
" to the template should use absolute names.\n"
"Target naming:\n"
" Your template should almost always define a built-in target with the\n"
" name the template invoker specified. For example, if you have an IDL\n"
" template and somebody does:\n"
" idl(\"foo\") {...\n"
" you will normally want this to expand to something defining a\n"
" source_set or static_library named \"foo\" (among other things you may\n"
" need). This way, when another target specifies a dependency on\n"
" \"foo\", the static_library or source_set will be linked.\n"
" It is also important that any other targets your template expands to\n"
" have globally unique names, or you will get collisions.\n"
" Access the invoking name in your template via the implicit\n"
" \"target_name\" variable. This should also be the basis of how other\n"
" targets that a template expands to to ensure uniquness.\n"
" A typical example would be a template that defines an action to\n"
" generate some source files, and a source_set to compile that source.\n"
" Your template would name the source_set \"target_name\" because\n"
" that's what you want external targets to depend on to link your code.\n"
" And you would name the action something like \"${target_name}_action\"\n"
" to make it unique. The source set would have a dependency on the\n"
" action to make it run.\n"
"Example of defining a template:\n"
" template(\"my_idl\") {\n"
" # Be nice and help callers debug problems by checking that the\n"
" # variables the template requires are defined. This gives a nice\n"
" # message rather than giving the user an error about an\n"
" # undefined variable in the file defining the template\n"
" #\n"
" # You can also use defined() to give default values to variables\n"
" # unspecified by the invoker.\n"
" assert(defined(invoker.sources),\n"
" \"Need sources in $target_name listing the idl files.\")\n"
" # Name of the intermediate target that does the code gen. This must\n"
" # incorporate the target name so it's unique across template\n"
" # instantiations.\n"
" code_gen_target_name = target_name + \"_code_gen\"\n"
" # Intermediate target to convert IDL to C source. Note that the name\n"
" # is based on the name the invoker of the template specified. This\n"
" # way, each time the template is invoked we get a unique\n"
" # intermediate action name (since all target names are in the global\n"
" # scope).\n"
" action_foreach(code_gen_target_name) {\n"
" # Access the scope defined by the invoker via the implicit\n"
" # \"invoker\" variable.\n"
" sources = invoker.sources\n"
" # Note that we need an absolute path for our script file name.\n"
" # The current directory when executing this code will be that of\n"
" # the invoker (this is why we can use the \"sources\" directly\n"
" # above without having to rebase all of the paths). But if we need\n"
" # to reference a script relative to the template file, we'll need\n"
" # to use an absolute path instead.\n"
" script = \"//tools/idl/\"\n"
" # Tell GN how to expand output names given the sources.\n"
" # See \"gn help source_expansion\" for more.\n"
" outputs = [ \"$target_gen_dir/{{source_name_part}}.cc\",\n"
" \"$target_gen_dir/{{source_name_part}}.h\" ]\n"
" }\n"
" # Name the source set the same as the template invocation so\n"
" # instancing this template produces something that other targets\n"
" # can link to in their deps.\n"
" source_set(target_name) {\n"
" # Generates the list of sources, we get these from the\n"
" # action_foreach above.\n"
" sources = get_target_outputs(\":$code_gen_target_name\")\n"
" # This target depends on the files produced by the above code gen\n"
" # target.\n"
" deps = [ \":$code_gen_target_name\" ]\n"
" }\n"
" }\n"
"Example of invoking the resulting template:\n"
" # This calls the template code above, defining target_name to be\n"
" # \"foo_idl_files\" and \"invoker\" to be the set of stuff defined in\n"
" # the curly brackets.\n"
" my_idl(\"foo_idl_files\") {\n"
" # Goes into the template as \"invoker.sources\".\n"
" sources = [ \"foo.idl\", \"bar.idl\" ]\n"
" }\n"
" # Here is a target that depends on our template.\n"
" executable(\"my_exe\") {\n"
" # Depend on the name we gave the template call above. Internally,\n"
" # this will produce a dependency from executable to the source_set\n"
" # inside the template (since it has this name), which will in turn\n"
" # depend on the code gen action.\n"
" deps = [ \":foo_idl_files\" ]\n"
" }\n";
Value RunTemplate(Scope* scope,
const FunctionCallNode* function,
const std::vector<Value>& args,
BlockNode* block,
Err* err) {
// TODO(brettw) determine if the function is built-in and throw an error if
// it is.
if (args.size() != 1) {
*err = Err(function->function(),
"Need exactly one string arg to template.");
return Value();
if (!args[0].VerifyTypeIs(Value::STRING, err))
return Value();
std::string template_name = args[0].string_value();
const Template* existing_template = scope->GetTemplate(template_name);
if (existing_template) {
*err = Err(function, "Duplicate template definition.",
"A template with this name was already defined.");
"Previous definition."));
return Value();
scope->AddTemplate(template_name, new Template(scope, function));
return Value();
} // namespace functions