Add initial prototype for the GN meta-buildsystem.

tools/gn/function_process_file_template.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/file_template.h"
+#include "tools/gn/functions.h"
+#include "tools/gn/parse_tree.h"
+
+/*
+process_file_template: Do template expansion over a list of files.
+
+  process_file_template(source_list, template)
+
+  process_file_template applies a template list to a source file list,
+  returning the result of applying each template to each source. This is
+  typically used for computing output file names from input files.
+
+Arguments:
+
+  The source_list is a list of file names.
+
+  The template can be a string or a list. If it is a list, multiple output
+  strings are generated for each input.
+
+  The following template substrings are used in the template arguments
+  and are replaced with the corresponding part of the input file name:
+
+    "{{source}}": The entire source name.
+
+    "{{source_name_part}}": The source name with no path or extension.
+
+Example:
+
+  sources = [
+    "foo.idl",
+    "bar.idl",
+  ]
+  myoutputs = process_file_template(
+      sources,
+      [ "$target_gen_dir/{{source_name_part}}.cc",
+        "$target_gen_dir/{{source_name_part}}.h" ])
+
+ The result in this case will be:
+    [ "/out/Debug/foo.cc"
+      "/out/Debug/foo.h"
+      "/out/Debug/bar.cc"
+      "/out/Debug/bar.h" ]
+*/
+Value ExecuteProcessFileTemplate(Scope* scope,
+                                 const FunctionCallNode* function,
+                                 const std::vector<Value>& args,
+                                 Err* err) {
+  if (args.size() != 2) {
+    *err = Err(function->function(), "Expected two arguments");
+    return Value();
+  }
+
+  FileTemplate file_template(args[1], err);
+  if (err->has_error())
+    return Value();
+
+  Value ret(function, Value::LIST);
+  file_template.Apply(args[0], function, &ret.list_value(), err);
+  return ret;
+}