[CP-Stable] Unset GIT_DIR and other variables before updating (flutter#166772)

Cherry picks flutter#165818

`update_engine_version.{ps1|sh}` needs to operate on a foreign repository.
When flutter is run in a git-hook, these environment variables will override our git calls location and corrupt the install.

Cherry pick notes: The files are diverging a bit; but the guts of the change were clean (ps1|sh) and the tests just needed some care.

Author: jtmcdole

CHANGELOG.md

@@ -27,6 +27,7 @@ INTERNAL NOTE
 ## Flutter 3.29 Changes
 
 ### [3.29.3](https://github.com/flutter/flutter/releases/tag/3.29.3)
+- [flutter/165818](https://github.com/flutter/flutter/pull/165818) - Unset `GIT_DIR` to enable flutter tool calls in githooks.
 - [flutter/163421](https://github.com/flutter/flutter/issues/163421) - Impeller,
   Android, Fixes Android Emulator crash when navigating to routes with backdrop
   blurs.

bin/internal/update_engine_version.ps1

@@ -16,6 +16,11 @@
 
 $ErrorActionPreference = "Stop"
 
+# When called from a submodule hook; these will override `git -C dir`
+$env:GIT_DIR = $null
+$env:GIT_INDEX_FILE = $null
+$env:GIT_WORK_TREE = $null
+
 $progName = Split-Path -parent $MyInvocation.MyCommand.Definition
 $flutterRoot = (Get-Item $progName).parent.parent.FullName
 

bin/internal/update_engine_version.sh

@@ -17,6 +17,11 @@
 
 set -e
 
+# When called from a submodule hook; these will override `git -C dir`
+unset GIT_DIR
+unset GIT_INDEX_FILE
+unset GIT_WORK_TREE
+
 # Allow overriding the intended engine version via FLUTTER_PREBUILT_ENGINE_VERSION.
 #
 # This is for systems, such as Github Actions, where we know ahead of time the

dev/tools/test/update_engine_version_test.dart

@@ -29,13 +29,13 @@ void main() {
     }
   }
 
-  io.ProcessResult run(String executable, List<String> args) {
+  io.ProcessResult run(String executable, List<String> args, {String? workingPath}) {
     print('Running "$executable ${args.join(" ")}"');
     final io.ProcessResult result = io.Process.runSync(
       executable,
       args,
       environment: environment,
-      workingDirectory: testRoot.root.absolute.path,
+      workingDirectory: workingPath ?? testRoot.root.absolute.path,
       includeParentEnvironment: false,
     );
     if (result.exitCode != 0) {
@@ -92,11 +92,68 @@ void main() {
     run('git', <String>['commit', '-m', 'tracking engine.version']);
   }
 
-  void setupRemote({required String remote}) {
-    run('git', <String>['remote', 'add', remote, testRoot.root.path]);
-    run('git', <String>['fetch', remote]);
+  void setupRemote({required String remote, String? rootPath}) {
+    run('git', <String>[
+      'remote',
+      'add',
+      remote,
+      rootPath ?? testRoot.root.path,
+    ], workingPath: rootPath);
+    run('git', <String>['fetch', remote], workingPath: rootPath);
   }
 
+  void initGitRepoWithBlankInitialCommit({String? workingPath}) {
+    run('git', <String>['init', '--initial-branch', 'master'], workingPath: workingPath);
+    run('git', <String>[
+      'config',
+      '--local',
+      'user.email',
+      '[email protected]',
+    ], workingPath: workingPath);
+    run('git', <String>['config', '--local', 'user.name', 'Test User'], workingPath: workingPath);
+    run('git', <String>['add', '.'], workingPath: workingPath);
+    run('git', <String>[
+      'commit',
+      '--allow-empty',
+      '-m',
+      'Initial commit',
+    ], workingPath: workingPath);
+  }
+
+  group('GIT_DIR', () {
+    late Directory externalGit;
+    late String externalHead;
+    setUp(() {
+      externalGit = localFs.systemTempDirectory.createTempSync('GIT_DIR_test.');
+      initGitRepoWithBlankInitialCommit(workingPath: externalGit.path);
+      setupRemote(remote: 'upstream', rootPath: externalGit.path);
+
+      externalHead =
+          (run('git', <String>['rev-parse', 'HEAD'], workingPath: externalGit.path).stdout
+                  as String)
+              .trim();
+    });
+
+    test('un-sets environment variables', () {
+      // Needs to happen before GIT_DIR is set
+      initGitRepoWithBlankInitialCommit();
+      setupRemote(remote: 'upstream');
+
+      environment['GIT_DIR'] = '${externalGit.path}/.git';
+      environment['GIT_INDEX_FILE'] = '${externalGit.path}/.git/index';
+      environment['GIT_WORK_TREE'] = externalGit.path;
+
+      runUpdateEngineVersion();
+
+      final String engineStamp = testRoot.binInternalEngineVersion.readAsStringSync().trim();
+      expect(engineStamp, isNot(equals(externalHead)));
+    });
+
+    tearDown(() {
+      externalGit.deleteSync(recursive: true);
+    });
+  });
+
   group('if FLUTTER_PREBUILT_ENGINE_VERSION is set', () {
     setUp(() {
       environment['FLUTTER_PREBUILT_ENGINE_VERSION'] = '123abc';