Allow sorting by file extension

file.rs

@@ -31,6 +31,11 @@ impl<'a> File<'a> {
         return File { path: path, stat: stat, name: filename };
     }
 
+    pub fn ext(&self) -> Option<&'a str> {
+        let re = regex!(r"\.(.+)$");
+        re.captures(self.name).map(|caps| caps.at(1))
+    }
+
     pub fn is_dotfile(&self) -> bool {
         self.name.starts_with(".")
     }

options.rs

@@ -1,7 +1,8 @@
 use file::File;
+use std::cmp::lexical_ordering;
 
 pub enum SortField {
-    Name, Size
+    Name, Extension, Size
 }
 
 pub struct Options {
@@ -14,6 +15,7 @@ impl SortField {
         match word.as_slice() {
             "name" => Name,
             "size" => Size,
+            "ext" => Extension,
             _ => fail!("Invalid sorting order"),
         }
     }
@@ -22,6 +24,11 @@ impl SortField {
         match *self {
             Name => files.sort_by(|a, b| a.name.cmp(&b.name)),
             Size => files.sort_by(|a, b| a.stat.size.cmp(&b.stat.size)),
+            Extension => files.sort_by(|a, b| {
+                let exts = a.ext().cmp(&b.ext());
+                let names = a.name.cmp(&b.name);
+                lexical_ordering(exts, names)
+            }),
         }
     }
 }