From 8e55e206a177fc046b1d2bac42acd86a40b00658 Mon Sep 17 00:00:00 2001
From: Alexander Wang <alex@terrastruct.com>
Date: Mon, 19 Dec 2022 13:20:41 -0800
Subject: [PATCH] write fmt only on diff

---
 ci/release/changelogs/next.md | 2 ++
 fmt.go                        | 7 ++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/ci/release/changelogs/next.md b/ci/release/changelogs/next.md
index f3c0d2a77..55bafe4af 100644
--- a/ci/release/changelogs/next.md
+++ b/ci/release/changelogs/next.md
@@ -3,3 +3,5 @@
 #### Improvements 🧹
 
 #### Bugfixes ⛑️
+
+- `d2 fmt` only rewrites if it has changes, instead of always rewriting. [#470](https://github.com/terrastruct/d2/pull/470)
diff --git a/fmt.go b/fmt.go
index e3a755a79..58a4f671b 100644
--- a/fmt.go
+++ b/fmt.go
@@ -33,5 +33,10 @@ func fmtCmd(ctx context.Context, ms *xmain.State) (err error) {
 		return err
 	}
 
-	return ms.WritePath(inputPath, []byte(d2format.Format(m)))
+	output := []byte(d2format.Format(m))
+	if !bytes.Equal(output, input) {
+		return ms.WritePath(inputPath, output)
+	}
+
+	return nil
 }