Start hacking checkstyle output in.

checkstyle now shows up on the option parser, and the code still
compiles/passes tests. Next up will be outputing the XML to stdout.

src/bin/rustfmt.rs

@@ -90,7 +90,7 @@ fn execute() -> i32 {
     opts.optopt("",
                 "write-mode",
                 "mode to write in (not usable when piping from stdin)",
-                "[replace|overwrite|display|diff|coverage]");
+                "[replace|overwrite|display|diff|coverage|checkstyle]");
     opts.optflag("", "skip-children", "don't reformat child modules");
 
     opts.optflag("",

src/config.rs

@@ -136,6 +136,8 @@ configuration_option_enum! { WriteMode:
     Coverage,
     // Unfancy stdout
     Plain,
+    // Output a checkstyle XML file.
+    Checkstyle,
 }
 
 // This trait and the following impl blocks are there so that we an use

src/filemap.rs

@@ -38,6 +38,7 @@ pub fn write_all_files(file_map: &FileMap,
         try!(write_file(&file_map[filename], filename, mode, config));
     }
 
+    // Output trailers for write mode.
     Ok(())
 }
 
@@ -142,6 +143,19 @@ pub fn write_file(text: &StringBuffer,
         WriteMode::Default => {
             unreachable!("The WriteMode should NEVER Be default at this point!");
         }
+        WriteMode::Checkstyle => {
+            // Generate the diff for the current file.
+            // Output the XML tags for the lines that are different.
+            // Use the new text as 'should be X'.
+        }
+        WriteMode::Return => {
+            // io::Write is not implemented for String, working around with
+            // Vec<u8>
+            let mut v = Vec::new();
+            try!(write_system_newlines(&mut v, text, config));
+            // won't panic, we are writing correct utf8
+            return Ok(Some(String::from_utf8(v).unwrap()));
+        }
     }
 
     Ok(None)