From 05f09c99373308dd6729d1c5f911d986ae6679e9 Mon Sep 17 00:00:00 2001
From: Alex Medinsh <alex.medinsh@gmail.com>
Date: Mon, 28 Apr 2025 19:35:11 +0300
Subject: [PATCH] Skip writing unchanged registrant files (#167262)

<!--
Thanks for filing a pull request!
Reviewers are typically assigned within a week of filing a request.
To learn more about code review, see our documentation on Tree Hygiene:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
-->

This PR adds logic to skip overwriting plugin registrant files if their
contents are unchanged.

Fixes https://github.com/flutter/flutter/issues/134899

## Pre-launch Checklist

- [X] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [X] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [X] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [X] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [X] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md
---
 .../lib/src/flutter_plugins.dart              | 13 ++++++++++
 .../test/general.shard/plugins_test.dart      | 25 +++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/packages/flutter_tools/lib/src/flutter_plugins.dart b/packages/flutter_tools/lib/src/flutter_plugins.dart
index 883cf48cc96..94d469dcc1b 100644
--- a/packages/flutter_tools/lib/src/flutter_plugins.dart
+++ b/packages/flutter_tools/lib/src/flutter_plugins.dart
@@ -15,6 +15,7 @@ import 'base/file_system.dart';
 import 'base/os.dart';
 import 'base/platform.dart';
 import 'base/template.dart';
+import 'base/utils.dart';
 import 'base/version.dart';
 import 'cache.dart';
 import 'compute_dev_dependencies.dart';
@@ -30,6 +31,14 @@ import 'platform_plugins.dart';
 import 'plugins.dart';
 import 'project.dart';
 
+Future<bool> _fileContentsUnchanged(File file, String renderedTemplate) async {
+  if (!await file.exists()) {
+    return false;
+  }
+  final List<int> fileBytes = await file.readAsBytes();
+  return listEquals(fileBytes, renderedTemplate.codeUnits);
+}
+
 Future<void> _renderTemplateToFile(
   String template,
   Object? context,
@@ -37,6 +46,10 @@ Future<void> _renderTemplateToFile(
   TemplateRenderer templateRenderer,
 ) async {
   final String renderedTemplate = templateRenderer.renderString(template, context);
+  if (await _fileContentsUnchanged(file, renderedTemplate)) {
+    globals.printTrace('Skipping generating ${file.basename} because it is up-to-date.');
+    return;
+  }
   await file.create(recursive: true);
   await file.writeAsString(renderedTemplate);
 }
diff --git a/packages/flutter_tools/test/general.shard/plugins_test.dart b/packages/flutter_tools/test/general.shard/plugins_test.dart
index 005a79c0a3a..6aecaad791c 100644
--- a/packages/flutter_tools/test/general.shard/plugins_test.dart
+++ b/packages/flutter_tools/test/general.shard/plugins_test.dart
@@ -1455,6 +1455,31 @@ flutter:
         },
       );
 
+      testUsingContext(
+        'Injecting does not overwrite unchanged registrant files',
+        () async {
+          createFakePlugin(fs);
+
+          await injectPlugins(flutterProject, releaseMode: false, linuxPlatform: true);
+
+          final File registrantHeader = linuxProject.managedDirectory.childFile(
+            'generated_plugin_registrant.h',
+          );
+          final DateTime headerLastModified = registrantHeader.lastModifiedSync();
+
+          await injectPlugins(flutterProject, releaseMode: false, linuxPlatform: true);
+
+          // Check that the last modified date is the same.
+          expect(registrantHeader.lastModifiedSync(), headerLastModified);
+        },
+        overrides: <Type, Generator>{
+          FileSystem: () => fs,
+          ProcessManager: () => FakeProcessManager.any(),
+          FeatureFlags: enableExplicitPackageDependencies,
+          Pub: FakePubWithPrimedDeps.new,
+        },
+      );
+
       testUsingContext(
         'Injecting creates generated macos registrant, but does not include Dart-only plugins',
         () async {