Reference written files relatively when possible.

tools/gn/filesystem_utils.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/filesystem_utils.h"
 
 #include <algorithm>
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
@@ skipping 314 matching lines @@
     return true;  // Output directory is hardcoded.
 
   *err = Err(origin, "File is not inside output directory.",
       "The given file should be in the output directory. Normally you would "
       "specify\n\"$target_out_dir/foo\" or "
       "\"$target_gen_dir/foo\". I interpreted this as\n\""
       + str + "\".");
   return false;
 }
 
+base::FilePath::StringType ComputeStringInOutputDir(const SourceDir& output_dir,
+                                           const SourceFile& output_file,
+                                           Err* err) {
+  if (output_file.is_source_absolute() != output_dir.is_source_absolute()) {
+    *err = Err(nullptr,
+        "Cannot determine if output file is in output directory",
+        "Absolute files/dirs are incomparable with source rooted ones.");
+    return base::FilePath::StringType();
+  }
+
+  const std::string& dir_str = output_dir.value();
+  const std::string& str = output_file.value();
+  if (str.compare(0, dir_str.length(), dir_str) != 0 ||
+      str.length() <= dir_str.length() ||
+      IsSlash(str[dir_str.length()])) {
+    *err = Err(nullptr, "File is not inside output directory.",
+        "The given file should be in the output directory. Normally you would "
+        "specify\n\"$target_out_dir/foo\" or "
+        "\"$target_gen_dir/foo\". I interpreted this as\n\""
+        + str + "\".");
+    return base::FilePath::StringType();
+  }
+  return base::FilePath::StringType(str.c_str() + dir_str.length(),
+                                    str.length() - dir_str.length());
+}
+
 bool IsPathAbsolute(const base::StringPiece& path) {
   if (path.empty())
     return false;
 
   if (!IsSlash(path[0])) {
 #if defined(OS_WIN)
     // Check for Windows system paths like "C:\foo".
     if (path.size() > 2 && path[1] == ':' && IsSlash(path[2]))
       return true;
 #endif
@@ skipping 469 matching lines @@
 
 SourceDir GetCurrentOutputDir(const Scope* scope) {
   return GetOutputDirForSourceDirAsOutputFile(
       scope->settings(), scope->GetSourceDir()).AsSourceDir(
           scope->settings()->build_settings());
 }
 
 SourceDir GetCurrentGenDir(const Scope* scope) {
   return GetGenDirForSourceDir(scope->settings(), scope->GetSourceDir());
 }