Add FilePath::FinalExtension and RemoveFinalExtension

base/files/file_path.cc

Index: base/files/file_path.cc
diff --git a/base/files/file_path.cc b/base/files/file_path.cc
index 90cf40f4da8453396bae2e473c9865aaa3f27ab2..15fa40fa1647b877e9ebfc6676ad279df1012728 100644
--- a/base/files/file_path.cc
+++ b/base/files/file_path.cc
@@ -18,6 +18,8 @@ const FilePath::CharType FilePath::kSeparators[] = FILE_PATH_LITERAL("/");
 #endif  // FILE_PATH_USES_WIN_SEPARATORS
 
 const FilePath::CharType FilePath::kCurrentDirectory[] = FILE_PATH_LITERAL(".");
+const FilePath::CharType FilePath::kParentDirectory[] = FILE_PATH_LITERAL("..");
+const FilePath::CharType FilePath::kExtensionSeparator = FILE_PATH_LITERAL('.');
 
 typedef FilePath::StringType StringType;
 
@@ -78,6 +80,17 @@ bool IsPathAbsolute(const StringType& path) {
 #endif  // FILE_PATH_USES_DRIVE_LETTERS
 }
 
+// Find the position of the '.' that separates the extension from the rest
+// of the file name. The position is relative to BaseName(), not value().

[Mark Mentovai, 2015/01/20 17:11:53]

The second sentence should be harsher: this function requires that its path
argument be a basename, not a full path.

[scottmg, 2015/01/20 18:01:27]

After simplifying below, just deleted this function.

+// Returns npos if it can't find an extension.
+StringType::size_type FinalExtensionSeparatorPosition(const StringType& path) {
+  // Special case "." and ".."
+  if (path == FilePath::kCurrentDirectory || path == FilePath::kParentDirectory)
+    return StringType::npos;
+
+  return path.rfind(FilePath::kExtensionSeparator);
+}
+
 }  // namespace
 
 FilePath::FilePath() {
@@ -190,6 +203,26 @@ FilePath FilePath::BaseName() const {
   return new_path;
 }
 
+StringType FilePath::FinalExtension() const {
+  FilePath base(BaseName());
+  const StringType::size_type dot = FinalExtensionSeparatorPosition(base.path_);
+  if (dot == StringType::npos)
+    return StringType();
+
+  return base.path_.substr(dot, StringType::npos);
+}
+
+FilePath FilePath::RemoveFinalExtension() const {
+  if (FinalExtension().empty())
+    return *this;
+
+  const StringType::size_type dot = FinalExtensionSeparatorPosition(path_);

[Mark Mentovai, 2015/01/20 17:11:53]

This logic winds up calling FinalExtension() twice, which doesn’t seem
necessary. Why not call it once and then lop off the extension based on its
length?

[scottmg, 2015/01/20 18:01:27]

Done.

+  if (dot == StringType::npos)
+    return *this;
+
+  return FilePath(path_.substr(0, dot));
+}
+
 FilePath FilePath::Append(const StringType& component) const {
   const StringType* appended = &component;
   StringType without_nuls;