ignore: impl Clone for DirEntry

There is a small hiccup here in that a `DirEntry` can embed errors
associated with reading an ignore file, which can be accessed and logged
by consumers if desired. That error type can contain an io::Error, which
isn't cloneable. We therefore implement Clone on our library's error
type in a way that re-creates the I/O error as best as possible.

Fixes #891

ignore/src/lib.rs

@@ -132,6 +132,44 @@ pub enum Error {
     InvalidDefinition,
 }
 
+impl Clone for Error {
+    fn clone(&self) -> Error {
+        match *self {
+            Error::Partial(ref errs) => Error::Partial(errs.clone()),
+            Error::WithLineNumber { line, ref err } => {
+                Error::WithLineNumber { line: line, err: err.clone() }
+            }
+            Error::WithPath { ref path, ref err } => {
+                Error::WithPath { path: path.clone(), err: err.clone() }
+            }
+            Error::WithDepth { depth, ref err } => {
+                Error::WithDepth { depth: depth, err: err.clone() }
+            }
+            Error::Loop { ref ancestor, ref child } => {
+                Error::Loop {
+                    ancestor: ancestor.clone(),
+                    child: child.clone()
+                }
+            }
+            Error::Io(ref err) => {
+                match err.raw_os_error() {
+                    Some(e) => Error::Io(io::Error::from_raw_os_error(e)),
+                    None => {
+                        Error::Io(io::Error::new(err.kind(), err.to_string()))
+                    }
+                }
+            }
+            Error::Glob { ref glob, ref err } => {
+                Error::Glob { glob: glob.clone(), err: err.clone() }
+            }
+            Error::UnrecognizedFileType(ref err) => {
+                Error::UnrecognizedFileType(err.clone())
+            }
+            Error::InvalidDefinition => Error::InvalidDefinition,
+        }
+    }
+}
+
 impl Error {
     /// Returns true if this is a partial error.
     ///