From 17add138607a557ab4c35f456054e5ba4fae5ea6 Mon Sep 17 00:00:00 2001
From: Simon Lydell <simon.lydell@gmail.com>
Date: Sun, 29 Jan 2017 16:09:22 +0100
Subject: [PATCH] Only write to files if the change (#511)

Fixes #506.
---
 bin/prettier.js | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/bin/prettier.js b/bin/prettier.js
index 16ea3381..2de67aae 100755
--- a/bin/prettier.js
+++ b/bin/prettier.js
@@ -191,13 +191,17 @@ if (stdin) {
       }
 
       if (write) {
-        fs.writeFile(filename, output, "utf8", err => {
-          if (err) {
-            console.error("Unable to write file: " + filename + "\n" + err);
-            // Don't exit the process if one file failed
-            process.exitCode = 2;
-          }
-        });
+        // Don't write the file if it won't change in order not to invalidate
+        // mtime based caches.
+        if (output !== input) {
+          fs.writeFile(filename, output, "utf8", err => {
+            if (err) {
+              console.error("Unable to write file: " + filename + "\n" + err);
+              // Don't exit the process if one file failed
+              process.exitCode = 2;
+            }
+          });
+        }
       } else {
         // Don't use `console.log` here since it adds an extra newline at the end.
         process.stdout.write(output);