Generate a warning if the return value of FilePath::Append is ignored.

base/file_path.h

 // Copyright (c) 2008 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.
 
 // FilePath is a container for pathnames stored in a platform's native string
 // type, providing containers for manipulation in according with the
 // platform's conventions for pathnames.  It supports the following path
 // types:
 //
 //                   POSIX            Windows
@@ skipping 49 matching lines @@
 // | void Function() {
 // |   FilePath log_file_path(kLogFileName);
 // |   [...]
 // | }
 
 #ifndef BASE_FILE_PATH_H_
 #define BASE_FILE_PATH_H_
 
 #include <string>
 
+#include "base/compiler_specific.h"
 #include "base/basictypes.h"
 
 // Windows-style drive letter support and pathname separator characters can be
 // enabled and disabled independently, to aid testing.  These #defines are
 // here so that the same setting can be used in both the implementation and
 // in the unit test.
 #if defined(OS_WIN)
 #define FILE_PATH_USES_DRIVE_LETTERS
 #define FILE_PATH_USES_WIN_SEPARATORS
 #endif  // OS_WIN
@@ skipping 54 matching lines @@
   // the root directory, returns a FilePath identifying the root directory;
   // this is the only situation in which BaseName will return an absolute path.
   FilePath BaseName() const;
 
   // Returns a FilePath by appending a separator and the supplied path
   // component to this object's path.  Append takes care to avoid adding
   // excessive separators if this object's path already ends with a separator.
   // If this object's path is kCurrentDirectory, a new FilePath corresponding
   // only to |component| is returned.  |component| must be a relative path;
   // it is an error to pass an absolute path.
-  FilePath Append(const StringType& component) const;
+  FilePath Append(const StringType& component) const WARN_UNUSED_RESULT;
 
   // Returns true if this FilePath contains an absolute path.  On Windows, an
   // absolute path begins with either a drive letter specification followed by
   // a separator character, or with two separator characters.  On POSIX
   // platforms, an absolute path begins with a separator character.
   bool IsAbsolute() const;
 
   // Older Chromium code assumes that paths are always wstrings.
   // This function converts a wstring to a FilePath, and is useful to smooth
   // porting that old code to the FilePath API.
@@ skipping 27 matching lines @@
 };
 
 // Macros for string literal initialization of FilePath::CharType[].
 #if defined(OS_POSIX)
 #define FILE_PATH_LITERAL(x) x
 #elif defined(OS_WIN)
 #define FILE_PATH_LITERAL(x) L ## x
 #endif  // OS_WIN
 
 #endif  // BASE_FILE_PATH_H_