Make base:ReplaceFile return an informative error.

base/file_util_posix.cc

 // Copyright (c) 2012 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 "base/file_util.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <fnmatch.h>
@@ skipping 214 matching lines @@
   if (rename(from_path.value().c_str(), to_path.value().c_str()) == 0)
     return true;
 
   if (!CopyDirectory(from_path, to_path, true))
     return false;
 
   Delete(from_path, true);
   return true;
 }
 
-bool ReplaceFile(const FilePath& from_path, const FilePath& to_path) {
+bool ReplaceFile(const FilePath& from_path, const FilePath& to_path,
+                 base::PlatformFileError* error) {
+  if (error)
+    *error = base::PLATFORM_FILE_OK;
   base::ThreadRestrictions::AssertIOAllowed();
-  return (rename(from_path.value().c_str(), to_path.value().c_str()) == 0);
+  if (rename(from_path.value().c_str(), to_path.value().c_str()) != 0) {
+    if (error)
+      *error = base::ErrnoToPlatformFileError(errno);
+    return false;
+  }
+  return true;

[jar (doing other things), 2013/05/07 01:12:36]

nit: switch the order of the results around, and you won't need curlies, or
extra indent.  This also puts the common case up front, and makes reading
(across an early return) easier.

if(...)
  return true
...

 }
 
 bool CopyDirectory(const FilePath& from_path,
                    const FilePath& to_path,
                    bool recursive) {
   base::ThreadRestrictions::AssertIOAllowed();
   // Some old callers of CopyDirectory want it to support wildcards.
   // After some discussion, we decided to fix those callers.
   // Break loudly here if anyone tries to do this.
   // TODO(evanm): remove this once we're sure it's ok.
@@ skipping 813 matching lines @@
       kFileSystemRoot, path, kRootUid, allowed_group_ids);
 }
 #endif  // defined(OS_MACOSX) && !defined(OS_IOS)
 
 int GetMaximumPathComponentLength(const FilePath& path) {
   base::ThreadRestrictions::AssertIOAllowed();
   return pathconf(path.value().c_str(), _PC_NAME_MAX);
 }
 
 }  // namespace file_util