[tool] Add a package-level pre-publish hook

script/tool/lib/src/common/repository_package.dart

@@ -66,6 +66,14 @@ class RepositoryPackage {
   /// The test directory containing the package's Dart tests.
   Directory get testDirectory => directory.childDirectory('test');
 
+  /// The path to the script that is run by the `custom-test` command.
+  File get customTestScript =>
+      directory.childDirectory('tool').childFile('run_tests.dart');
+
+  /// The path to the script that is run before publishing.
+  File get prePublishScript =>
+      directory.childDirectory('tool').childFile('pre_publish.dart');
+
   /// Returns the directory containing support for [platform].
   Directory platformDirectory(FlutterPlatform platform) {
     late final String directoryName;

script/tool/lib/src/custom_test_command.dart

@@ -8,7 +8,6 @@ import 'common/package_looping_command.dart';
 import 'common/pub_utils.dart';
 import 'common/repository_package.dart';
 
-const String _scriptName = 'run_tests.dart';
 const String _legacyScriptName = 'run_tests.sh';
 
 /// A command to run custom, package-local tests on packages.
@@ -32,13 +31,14 @@ class CustomTestCommand extends PackageLoopingCommand {
 
   @override
   final String description = 'Runs package-specific custom tests defined in '
-      "a package's tool/$_scriptName file.\n\n"
+      "a package's custom test script.\n\n"
       'This command requires "dart" to be in your path.';
 
   @override
   Future<PackageResult> runForPackage(RepositoryPackage package) async {
-    final File script =
-        package.directory.childDirectory('tool').childFile(_scriptName);
+    final File script = package.customTestScript;
+    final String relativeScriptPath =
+        getRelativePosixPath(script, from: package.directory);
     final File legacyScript = package.directory.childFile(_legacyScriptName);
     String? customSkipReason;
     bool ranTests = false;
@@ -52,7 +52,7 @@ class CustomTestCommand extends PackageLoopingCommand {
       }
 
       final int testExitCode = await processRunner.runAndStream(
-          'dart', <String>['run', 'tool/$_scriptName'],
+          'dart', <String>['run', relativeScriptPath],
           workingDir: package.directory);
       if (testExitCode != 0) {
         return PackageResult.fail();
@@ -64,7 +64,7 @@ class CustomTestCommand extends PackageLoopingCommand {
     if (legacyScript.existsSync()) {
       if (platform.isWindows) {
         customSkipReason = '$_legacyScriptName is not supported on Windows. '
-            'Please migrate to $_scriptName.';
+            'Please migrate to $relativeScriptPath.';
       } else {
         final int exitCode = await processRunner.runAndStream(
             legacyScript.path, <String>[],
@@ -77,7 +77,8 @@ class CustomTestCommand extends PackageLoopingCommand {
     }
 
     if (!ranTests) {
-      return PackageResult.skip(customSkipReason ?? 'No custom tests');
+      return PackageResult.skip(
+          customSkipReason ?? 'No $relativeScriptPath file');
     }
 
     return PackageResult.success();

script/tool/lib/src/publish_check_command.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io' as io;
 
+import 'package:file/file.dart';
 import 'package:http/http.dart' as http;
 import 'package:pub_semver/pub_semver.dart';
 
@@ -83,6 +84,9 @@ class PublishCheckCommand extends PackageLoopingCommand {
           isError: true);
       result = _PublishCheckResult.error;
     }
+    if (!await _validatePrePublishHook(package)) {
+      result = _PublishCheckResult.error;
+    }
 
     if (result.index > _overallResult.index) {
       _overallResult = result;
@@ -268,6 +272,33 @@ HTTP response: ${pubVersionFinderResponse.httpResponse.body}
     return package.authorsFile.existsSync();
   }
 
+  Future<bool> _validatePrePublishHook(RepositoryPackage package) async {
+    final File script = package.prePublishScript;
+    if (!script.existsSync()) {
+      // If there's no custom step, then it can't block publishing.
+      return true;
+    }
+    final String relativeScriptPath =
+        getRelativePosixPath(script, from: package.directory);
+    print('Running pre-publish hook $relativeScriptPath...');
+
+    // Ensure that dependencies are available.
+    if (!await runPubGet(package, processRunner, platform)) {
+      _printImportantStatusMessage('Failed to get depenedencies',
+          isError: true);
+      return false;
+    }
+
+    final int exitCode = await processRunner.runAndStream(
+        'dart', <String>['run', relativeScriptPath],
+        workingDir: package.directory);
+    if (exitCode != 0) {
+      _printImportantStatusMessage('Pre-publish script failed.', isError: true);
+      return false;
+    }
+    return true;
+  }
+
   void _printImportantStatusMessage(String message, {required bool isError}) {
     final String statusMessage = '${isError ? 'ERROR' : 'SUCCESS'}: $message';
     if (getBoolArg(_machineFlag)) {

script/tool/lib/src/publish_command.dart

@@ -21,6 +21,7 @@ import 'common/git_version_finder.dart';
 import 'common/output_utils.dart';
 import 'common/package_command.dart';
 import 'common/package_looping_command.dart';
+import 'common/pub_utils.dart';
 import 'common/pub_version_finder.dart';
 import 'common/repository_package.dart';
 
@@ -201,6 +202,10 @@ class PublishCommand extends PackageLoopingCommand {
       return checkResult;
     }
 
+    if (!await _runPrePublishScript(package)) {
+      return PackageResult.fail(<String>['pre-publish failed']);
+    }
+
     if (!await _checkGitStatus(package)) {
       return PackageResult.fail(<String>['uncommitted changes']);
     }
@@ -375,6 +380,31 @@ Safe to ignore if the package is deleted in this commit.
     return getRemoteUrlResult.stdout as String?;
   }
 
+  Future<bool> _runPrePublishScript(RepositoryPackage package) async {
+    final File script = package.prePublishScript;
+    if (!script.existsSync()) {
+      return true;
+    }
+    final String relativeScriptPath =
+        getRelativePosixPath(script, from: package.directory);
+    print('Running pre-publish hook $relativeScriptPath...');
+
+    // Ensure that dependencies are available.
+    if (!await runPubGet(package, processRunner, platform)) {
+      printError('Failed to get depenedencies');
+      return false;
+    }
+
+    final int exitCode = await processRunner.runAndStream(
+        'dart', <String>['run', relativeScriptPath],
+        workingDir: package.directory);
+    if (exitCode != 0) {
+      printError('Pre-publish script failed.');
+      return false;
+    }
+    return true;
+  }
+
   Future<bool> _publish(RepositoryPackage package) async {
     print('Publishing...');
     print('Running `pub publish ${_publishFlags.join(' ')}` in '

script/tool/test/publish_check_command_test.dart

@@ -369,6 +369,88 @@ void main() {
           ));
     });
 
+    group('pre-publish script', () {
+      test('runs if present', () async {
+        final RepositoryPackage package =
+            createFakePackage('a_package', packagesDir, examples: <String>[]);
+        package.prePublishScript.createSync(recursive: true);
+
+        final List<String> output = await runCapturingPrint(runner, <String>[
+          'publish-check',
+        ]);
+
+        expect(
+          output,
+          containsAllInOrder(<Matcher>[
+            contains('Running pre-publish hook tool/pre_publish.dart...'),
+          ]),
+        );
+        expect(
+            processRunner.recordedCalls,
+            containsAllInOrder(<ProcessCall>[
+              ProcessCall(
+                  'dart',
+                  const <String>[
+                    'pub',
+                    'get',
+                  ],
+                  package.directory.path),
+              ProcessCall(
+                  'dart',
+                  const <String>[
+                    'run',
+                    'tool/pre_publish.dart',
+                  ],
+                  package.directory.path),
+            ]));
+      });
+
+      test('causes command failure if it fails', () async {
+        final RepositoryPackage package = createFakePackage(
+            'a_package', packagesDir,
+            isFlutter: true, examples: <String>[]);
+        package.prePublishScript.createSync(recursive: true);
+
+        processRunner.mockProcessesForExecutable['dart'] = <FakeProcessInfo>[
+          FakeProcessInfo(MockProcess(exitCode: 1),
+              <String>['run']), // run tool/pre_publish.dart
+        ];
+
+        Error? commandError;
+        final List<String> output = await runCapturingPrint(runner, <String>[
+          'publish-check',
+        ], errorHandler: (Error e) {
+          commandError = e;
+        });
+
+        expect(commandError, isA<ToolExit>());
+        expect(
+          output,
+          containsAllInOrder(<Matcher>[
+            contains('Pre-publish script failed.'),
+          ]),
+        );
+        expect(
+            processRunner.recordedCalls,
+            containsAllInOrder(<ProcessCall>[
+              ProcessCall(
+                  getFlutterCommand(mockPlatform),
+                  const <String>[
+                    'pub',
+                    'get',
+                  ],
+                  package.directory.path),
+              ProcessCall(
+                  'dart',
+                  const <String>[
+                    'run',
+                    'tool/pre_publish.dart',
+                  ],
+                  package.directory.path),
+            ]));
+      });
+    });
+
     test(
         '--machine: Log JSON with status:no-publish and correct human message, if there are no packages need to be published. ',
         () async {

script/tool/test/publish_command_test.dart

@@ -141,6 +141,91 @@ void main() {
     });
   });
 
+  group('pre-publish script', () {
+    test('runs if present', () async {
+      final RepositoryPackage package =
+          createFakePackage('foo', packagesDir, examples: <String>[]);
+      package.prePublishScript.createSync(recursive: true);
+
+      final List<String> output =
+          await runCapturingPrint(commandRunner, <String>[
+        'publish',
+        '--packages=foo',
+      ]);
+
+      expect(
+        output,
+        containsAllInOrder(<Matcher>[
+          contains('Running pre-publish hook tool/pre_publish.dart...'),
+        ]),
+      );
+      expect(
+          processRunner.recordedCalls,
+          containsAllInOrder(<ProcessCall>[
+            ProcessCall(
+                'dart',
+                const <String>[
+                  'pub',
+                  'get',
+                ],
+                package.directory.path),
+            ProcessCall(
+                'dart',
+                const <String>[
+                  'run',
+                  'tool/pre_publish.dart',
+                ],
+                package.directory.path),
+          ]));
+    });
+
+    test('causes command failure if it fails', () async {
+      final RepositoryPackage package = createFakePackage('foo', packagesDir,
+          isFlutter: true, examples: <String>[]);
+      package.prePublishScript.createSync(recursive: true);
+
+      processRunner.mockProcessesForExecutable['dart'] = <FakeProcessInfo>[
+        FakeProcessInfo(MockProcess(exitCode: 1),
+            <String>['run']), // run tool/pre_publish.dart
+      ];
+
+      Error? commandError;
+      final List<String> output =
+          await runCapturingPrint(commandRunner, <String>[
+        'publish',
+        '--packages=foo',
+      ], errorHandler: (Error e) {
+        commandError = e;
+      });
+
+      expect(commandError, isA<ToolExit>());
+      expect(
+        output,
+        containsAllInOrder(<Matcher>[
+          contains('Pre-publish script failed.'),
+        ]),
+      );
+      expect(
+          processRunner.recordedCalls,
+          containsAllInOrder(<ProcessCall>[
+            ProcessCall(
+                getFlutterCommand(platform),
+                const <String>[
+                  'pub',
+                  'get',
+                ],
+                package.directory.path),
+            ProcessCall(
+                'dart',
+                const <String>[
+                  'run',
+                  'tool/pre_publish.dart',
+                ],
+                package.directory.path),
+          ]));
+    });
+  });
+
   group('Publishes package', () {
     test('while showing all output from pub publish to the user', () async {
       createFakePlugin('plugin1', packagesDir, examples: <String>[]);