impl Debug for ReadDir

It is good practice to implement Debug for public types, and
indicating what directory you're reading seems useful.

Signed-off-by: David Henningsson <diwic@ubuntu.com>

src/libstd/fs.rs

@@ -83,6 +83,7 @@ pub struct Metadata(fs_imp::FileAttr);
 ///
 /// [`io::Result`]: ../io/type.Result.html
 #[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
 pub struct ReadDir(fs_imp::ReadDir);
 
 /// Entries returned by the [`ReadDir`] iterator.

src/libstd/sys/unix/fs.rs

@@ -193,6 +193,14 @@ impl FromInner<u32> for FilePermissions {
     }
 }
 
+impl fmt::Debug for ReadDir {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // This will only be called from std::fs::ReadDir, which will add a "ReadDir()" frame.
+        // Thus the result will be e g 'ReadDir("/home")'
+        fmt::Debug::fmt(&*self.root, f)
+    }
+}
+
 impl Iterator for ReadDir {
     type Item = io::Result<DirEntry>;
 

src/libstd/sys/windows/fs.rs

@@ -81,6 +81,14 @@ pub struct FilePermissions { attrs: c::DWORD }
 
 pub struct DirBuilder;
 
+impl fmt::Debug for ReadDir {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // This will only be called from std::fs::ReadDir, which will add a "ReadDir()" frame.
+        // Thus the result will be e g 'ReadDir("C:\")'
+        fmt::Debug::fmt(&*self.root, f)
+    }
+}
+
 impl Iterator for ReadDir {
     type Item = io::Result<DirEntry>;
     fn next(&mut self) -> Option<io::Result<DirEntry>> {