docs: Clarify return type of lookup_project_file

diff --git a/src/bin/rustfmt.rs b/src/bin/rustfmt.rs
index 3bd575bfe873f6a8a36cd9b4511ce28b030e86d7..14cb63db7d506729db60c65b95d950f4ba835366 100644 (file)
--- a/src/bin/rustfmt.rs
+++ b/src/bin/rustfmt.rs
@@ -43,7 +43,8 @@ enum Operation {
     Stdin(String, WriteMode),
 }
 
-/// Try to find a project file in the given directory and its parents.
+/// Try to find a project file in the given directory and its parents. Returns the path of a the
+/// nearest project file if one exists, or `None` if no project file was found.
 fn lookup_project_file(dir: &Path) -> io::Result<Option<PathBuf>> {
     let mut current = if dir.is_relative() {
         try!(env::current_dir()).join(dir)