Implement Display for PrefPathError.

src/sdl2/filesystem.rs

@@ -1,4 +1,5 @@
 use std::ffi::{CStr, CString, NulError};
+use std::fmt;
 use get_error;
 use libc::c_char;
 
@@ -24,6 +25,18 @@ pub enum PrefPathError {
     SdlError(String),
 }
 
+impl fmt::Display for PrefPathError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use self::PrefPathError::*;
+
+        match *self {
+            InvalidOrganizationName(ref e) => write!(f, "Invalid organization name: {}", e),
+            InvalidApplicationName(ref e) => write!(f, "Invalid application name: {}", e),
+            SdlError(ref e) => write!(f, "SDL error: {}", e)
+        }
+    }
+}
+
 // TODO: Change to OsStr or something?
 /// Return the preferred directory for the application to write files on this
 /// system, based on the given organization and application name.