--file_lines argument now supports "stdin"

src/bin/rustfmt.rs

@@ -217,17 +217,16 @@ fn execute(opts: &Options) -> FmtResult<Summary> {
             // write_mode is always Plain for Stdin.
             config.write_mode = WriteMode::Plain;
 
+            // parse file_lines
+            if let Some(ref file_lines) = matches.opt_str("file-lines") {
+                config.file_lines = try!(file_lines.parse());
+            }
+
             Ok(run(Input::Text(input), &config))
         }
-        Operation::Format {
-            mut files,
-            config_path,
-        } => {
+        Operation::Format { files, config_path } => {
             let options = try!(CliOptions::from_matches(&matches));
 
-            // Add any additional files that were specified via `--file-lines`.
-            files.extend(options.file_lines.files().cloned().map(PathBuf::from));
-
             let mut config = Config::default();
             let mut path = None;
             // Load the config path file if provided
@@ -345,9 +344,8 @@ fn determine_operation(matches: &Matches) -> FmtResult<Operation> {
                       Some(dir)
                   });
 
-    // if no file argument is supplied and `--file-lines` is not specified, read from stdin
-    if matches.free.is_empty() && !matches.opt_present("file-lines") {
-
+    // if no file argument is supplied, read from stdin
+    if matches.free.is_empty() {
         let mut buffer = String::new();
         try!(io::stdin().read_to_string(&mut buffer));
 
@@ -357,7 +355,6 @@ fn determine_operation(matches: &Matches) -> FmtResult<Operation> {
                   });
     }
 
-    // We append files from `--file-lines` later in `execute()`.
     let files: Vec<_> = matches.free.iter().map(PathBuf::from).collect();
 
     Ok(Operation::Format {

src/file_lines.rs

@@ -162,6 +162,10 @@ impl<'a> iter::Iterator for Files<'a> {
 }
 
 fn canonicalize_path_string(s: &str) -> Result<String, ()> {
+    if s == "stdin" {
+        return Ok(s.to_string());
+    }
+
     match path::PathBuf::from(s).canonicalize() {
         Ok(canonicalized) => canonicalized.to_str().map(|s| s.to_string()).ok_or(()),
         _ => Err(()),