[tools] Ignore comments in federated safety check

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

@@ -211,9 +211,9 @@ Future<bool> _isGradleTestDependencyChange(List<String> pathComponents,
     return false;
   }
   final List<String> diff = await git.getDiffContents(targetPath: repoPath);
-  final RegExp changeLine = RegExp(r'[+-] ');
+  final RegExp changeLine = RegExp(r'^[+-] ');
   final RegExp testDependencyLine =
-      RegExp(r'[+-]\s*(?:androidT|t)estImplementation\s');
+      RegExp(r'^[+-]\s*(?:androidT|t)estImplementation\s');
   bool foundTestDependencyChange = false;
   for (final String line in diff) {
     if (!changeLine.hasMatch(line) ||

script/tool/lib/src/federation_safety_check_command.dart

@@ -85,7 +85,8 @@ class FederationSafetyCheckCommand extends PackageLoopingCommand {
         packageName = relativeComponents.removeAt(0);
       }
 
-      if (relativeComponents.last.endsWith('.dart')) {
+      if (relativeComponents.last.endsWith('.dart') &&
+          !await _changeIsCommentOnly(gitVersionFinder, path)) {
         _changedDartFiles[packageName] ??= <String>[];
         _changedDartFiles[packageName]!
             .add(p.posix.joinAll(relativeComponents));
@@ -196,4 +197,31 @@ class FederationSafetyCheckCommand extends PackageLoopingCommand {
     }
     return pubspec.version != previousVersion;
   }
+
+  Future<bool> _changeIsCommentOnly(
+      GitVersionFinder git, String repoPath) async {
+    if (git == null) {
+      return false;
+    }
+    final List<String> diff = await git.getDiffContents(targetPath: repoPath);
+    final RegExp changeLine = RegExp(r'^[+-] ');
+    // This will not catch /**/-style comments, but false negatives are fine
+    // (and in practice, we almost never use that comment style in Dart code).
+    final RegExp commentLine = RegExp(r'^[+-]\s*//');
+    bool foundComment = false;
+    for (final String line in diff) {
+      if (!changeLine.hasMatch(line) ||
+          line.startsWith('--- ') ||
+          line.startsWith('+++ ')) {
+        continue;
+      }
+      if (!commentLine.hasMatch(line)) {
+        return false;
+      }
+      foundComment = true;
+    }
+    // Only return true if a comment change was found, as a fail-safe against
+    // against having the wrong (e.g., incorrectly empty) diff output.
+    return foundComment;
+  }
 }

script/tool/test/federation_safety_check_command_test.dart

@@ -202,6 +202,23 @@ void main() {
     final RepositoryPackage platformInterface =
         createFakePlugin('foo_platform_interface', pluginGroupDir);
 
+    const String appFacingChanges = '''
+diff --git a/packages/foo/foo/lib/foo.dart b/packages/foo/foo/lib/foo.dart
+index abc123..def456 100644
+--- a/packages/foo/foo/lib/foo.dart
++++ b/packages/foo/foo/lib/foo.dart
+@@ -51,6 +51,9 @@ Future<bool> launchUrl(
+   return true;
+ }
+
++// This is a new method
++bool foo() => true;
++
+ // This in an existing method
+ void aMethod() {
+   // Do things.
+''';
+
     final String changedFileOutput = <File>[
       appFacing.libDirectory.childFile('foo.dart'),
       implementation.libDirectory.childFile('foo.dart'),
@@ -210,6 +227,12 @@ void main() {
     ].map((File file) => file.path).join('\n');
     processRunner.mockProcessesForExecutable['git-diff'] = <FakeProcessInfo>[
       FakeProcessInfo(MockProcess(stdout: changedFileOutput)),
+      // Ensure that a change with both a comment and non-comment addition is
+      // counted, to validate change analysis.
+      FakeProcessInfo(MockProcess(stdout: appFacingChanges),
+          <String>['', 'HEAD', '--', '/packages/foo/foo/lib/foo.dart']),
+      // The others diffs don't need to be specified, since empty diff is also
+      // treated as a non-comment change.
     ];
 
     Error? commandError;
@@ -308,6 +331,141 @@ void main() {
     );
   });
 
+  test('ignores comment-only changes in implementation packages', () async {
+    final Directory pluginGroupDir = packagesDir.childDirectory('foo');
+    final RepositoryPackage implementation =
+        createFakePlugin('foo_bar', pluginGroupDir);
+    final RepositoryPackage platformInterface =
+        createFakePlugin('foo_platform_interface', pluginGroupDir);
+
+    final String changedFileOutput = <File>[
+      implementation.libDirectory.childFile('foo.dart'),
+      platformInterface.pubspecFile,
+      platformInterface.libDirectory.childFile('foo.dart'),
+    ].map((File file) => file.path).join('\n');
+
+    const String platformInterfaceChanges = '''
+diff --git a/packages/foo/foo_platform_interface/lib/foo.dart b/packages/foo/foo_platform_interface/lib/foo.dart
+index abc123..def456 100644
+--- a/packages/foo/foo_platform_interface/lib/foo.dart
++++ b/packages/foo/foo_platform_interface/lib/foo.dart
+@@ -51,6 +51,7 @@ Future<bool> launchUrl(
+ enum Foo {
+   a,
+   b,
++  c,
+   d,
+   e,
+ }
+''';
+    const String implementationChanges = '''
+diff --git a/packages/foo/foo_bar/lib/foo.dart b/packages/foo/foo_bar/lib/foo.dart
+index abc123..def456 100644
+--- a/packages/foo/foo_bar/lib/foo.dart
++++ b/packages/foo/foo_bar/lib/foo.dart
+@@ -51,6 +51,7 @@ Future<bool> launchUrl(
+ }
+
+ void foo() {
++  // ignore: exhaustive_cases
+   switch(a_foo) {
+     case a:
+       // Do things
+''';
+
+    processRunner.mockProcessesForExecutable['git-diff'] = <FakeProcessInfo>[
+      FakeProcessInfo(
+          MockProcess(stdout: changedFileOutput), <String>['--name-only']),
+      FakeProcessInfo(MockProcess(stdout: implementationChanges),
+          <String>['', 'HEAD', '--', '/packages/foo/foo_bar/lib/foo.dart']),
+      FakeProcessInfo(MockProcess(stdout: platformInterfaceChanges), <String>[
+        '',
+        'HEAD',
+        '--',
+        '/packages/foo/foo_platform_interface/lib/foo.dart'
+      ]),
+    ];
+
+    final List<String> output =
+        await runCapturingPrint(runner, <String>['federation-safety-check']);
+
+    expect(
+      output,
+      containsAllInOrder(<Matcher>[
+        contains('Running for foo_bar...'),
+        contains('No Dart changes.'),
+      ]),
+    );
+  });
+
+  test('ignores comment-only changes in platform interface packages', () async {
+    final Directory pluginGroupDir = packagesDir.childDirectory('foo');
+    final RepositoryPackage implementation =
+        createFakePlugin('foo_bar', pluginGroupDir);
+    final RepositoryPackage platformInterface =
+        createFakePlugin('foo_platform_interface', pluginGroupDir);
+
+    final String changedFileOutput = <File>[
+      implementation.libDirectory.childFile('foo.dart'),
+      platformInterface.pubspecFile,
+      platformInterface.libDirectory.childFile('foo.dart'),
+    ].map((File file) => file.path).join('\n');
+
+    const String platformInterfaceChanges = '''
+diff --git a/packages/foo/foo_platform_interface/lib/foo.dart b/packages/foo/foo_platform_interface/lib/foo.dart
+index abc123..def456 100644
+--- a/packages/foo/foo_platform_interface/lib/foo.dart
++++ b/packages/foo/foo_platform_interface/lib/foo.dart
+@@ -51,6 +51,8 @@ Future<bool> launchUrl(
+   // existing comment
+   // existing comment
+   // existing comment
++  //
++  // additional comment
+   void foo() {
+     some code;
+   }
+''';
+    const String implementationChanges = '''
+diff --git a/packages/foo/foo_bar/lib/foo.dart b/packages/foo/foo_bar/lib/foo.dart
+index abc123..def456 100644
+--- a/packages/foo/foo_bar/lib/foo.dart
++++ b/packages/foo/foo_bar/lib/foo.dart
+@@ -51,6 +51,7 @@ Future<bool> launchUrl(
+ }
+
+ void foo() {
++  new code;
+   existing code;
+   ...
+   ...
+''';
+
+    processRunner.mockProcessesForExecutable['git-diff'] = <FakeProcessInfo>[
+      FakeProcessInfo(
+          MockProcess(stdout: changedFileOutput), <String>['--name-only']),
+      FakeProcessInfo(MockProcess(stdout: implementationChanges),
+          <String>['', 'HEAD', '--', '/packages/foo/foo_bar/lib/foo.dart']),
+      FakeProcessInfo(MockProcess(stdout: platformInterfaceChanges), <String>[
+        '',
+        'HEAD',
+        '--',
+        '/packages/foo/foo_platform_interface/lib/foo.dart'
+      ]),
+    ];
+
+    final List<String> output =
+        await runCapturingPrint(runner, <String>['federation-safety-check']);
+
+    expect(
+      output,
+      containsAllInOrder(<Matcher>[
+        contains('Running for foo_bar...'),
+        contains('No public code changes for foo_platform_interface.'),
+      ]),
+    );
+  });
+
   test('allows things that look like mass changes, with warning', () async {
     final Directory pluginGroupDir = packagesDir.childDirectory('foo');
     final RepositoryPackage appFacing = createFakePlugin('foo', pluginGroupDir);