From 9fdf64baa217c2001a36fae0bf6fb23f5f8447c6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kat=20March=C3=A1n?= <kzm@sykosomatic.org>
Date: Wed, 28 Jun 2017 21:26:32 -0700
Subject: [PATCH] save: only write package.json and locks if files have changed

Fixes: https://github.com/npm/npm/issues/17173
---
 lib/install/save.js |  7 ++++++-
 lib/shrinkwrap.js   | 21 ++++++++++++++-------
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/lib/install/save.js b/lib/install/save.js
index 56a4a892ad4..66b4a4ea9ad 100644
--- a/lib/install/save.js
+++ b/lib/install/save.js
@@ -123,7 +123,12 @@ function savePackageJson (tree, next) {
     }
 
     var json = JSON.stringify(tree.package, null, indent) + '\n'
-    writeFileAtomic(saveTarget, json, next)
+    if (json === packagejson) {
+      log.verbose('shrinkwrap', 'skipping write for package.json because there were no changes.')
+      next()
+    } else {
+      writeFileAtomic(saveTarget, json, next)
+    }
   }))
 }
 
diff --git a/lib/shrinkwrap.js b/lib/shrinkwrap.js
index 48c32486385..2a1c01d3aa1 100644
--- a/lib/shrinkwrap.js
+++ b/lib/shrinkwrap.js
@@ -163,14 +163,20 @@ function save (dir, pkginfo, opts, cb) {
       )
       const updated = updateLockfileMetadata(pkginfo, pkg && pkg.data)
       const swdata = JSON.stringify(updated, null, info.indent) + '\n'
-      writeFileAtomic(info.path, swdata, (err) => {
-        if (err) return cb(err)
-        if (opts.silent) return cb(null, pkginfo)
-        if (!shrinkwrap && !lockfile) {
-          log.notice('', `created a lockfile as ${path.basename(info.path)}. You should commit this file.`)
-        }
+      if (swdata === info.raw) {
+        // skip writing if file is identical
+        log.verbose('shrinkwrap', `skipping write for ${path.basename(info.path)} because there were no changes.`)
         cb(null, pkginfo)
-      })
+      } else {
+        writeFileAtomic(info.path, swdata, (err) => {
+          if (err) return cb(err)
+          if (opts.silent) return cb(null, pkginfo)
+          if (!shrinkwrap && !lockfile) {
+            log.notice('', `created a lockfile as ${path.basename(info.path)}. You should commit this file.`)
+          }
+          cb(null, pkginfo)
+        })
+      }
     }
   ).then((file) => {
   }, cb)
@@ -216,6 +222,7 @@ function checkPackageFile (dir, name) {
   ).then((data) => {
     return {
       path: file,
+      raw: data,
       data: JSON.parse(data),
       indent: detectIndent(data).indent || 2
     }