Support for source_target_relative expansion in GN

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/functions.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/settings.h"
 #include "tools/gn/substitution_list.h"
 #include "tools/gn/substitution_writer.h"
@@ skipping 75 matching lines @@
     if (!subst.Parse(list, template_arg.origin(), err))
       return Value();
   } else if (template_arg.type() == Value::LIST) {
     if (!subst.Parse(template_arg, err))
       return Value();
   } else {
     *err = Err(template_arg, "Not a string or a list.");
     return Value();
   }
 
+  auto& types = subst.required_types();
+  if (std::find(types.begin(), types.end(),
+                SUBSTITUTION_SOURCE_TARGET_RELATIVE) != types.end()) {
+    *err = Err(template_arg, "Not a valid substitution type for the function.");
+    return Value();
+  }
+
   SubstitutionWriter::ApplyListToSourcesAsString(
-      scope->settings(), subst, input_files, &result_files);
+      nullptr, scope->settings(), subst, input_files, &result_files);
 
   // Convert the list of strings to the return Value.
   Value ret(function, Value::LIST);
   ret.list_value().reserve(result_files.size());
   for (const auto& file : result_files)
     ret.list_value().push_back(Value(function, file));
 
   return ret;
 }
 
 }  // namespace functions