Add supported OS version tables to READMEs (#5106)

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

@@ -48,6 +48,9 @@ class RepositoryPackage {
   /// The package's top-level pubspec.yaml.
   File get pubspecFile => directory.childFile('pubspec.yaml');
 
+  /// The package's top-level README.
+  File get readmeFile => directory.childFile('README.md');
+
   late final Pubspec _parsedPubspec =
       Pubspec.parse(pubspecFile.readAsStringSync());
 
@@ -62,6 +65,12 @@ class RepositoryPackage {
       directory.parent.basename != 'packages' &&
       directory.basename.startsWith(directory.parent.basename);
 
+  /// True if this appears to be the app-facing package of a federated plugin,
+  /// according to repository conventions.
+  bool get isAppFacing =>
+      directory.parent.basename != 'packages' &&
+      directory.basename == directory.parent.basename;
+
   /// True if this appears to be a platform interface package, according to
   /// repository conventions.
   bool get isPlatformInterface =>

script/tool/lib/src/main.dart

@@ -26,6 +26,7 @@ import 'native_test_command.dart';
 import 'publish_check_command.dart';
 import 'publish_plugin_command.dart';
 import 'pubspec_check_command.dart';
+import 'readme_check_command.dart';
 import 'test_command.dart';
 import 'version_check_command.dart';
 import 'xcode_analyze_command.dart';
@@ -65,6 +66,7 @@ void main(List<String> args) {
     ..addCommand(PublishCheckCommand(packagesDir))
     ..addCommand(PublishPluginCommand(packagesDir))
     ..addCommand(PubspecCheckCommand(packagesDir))
+    ..addCommand(ReadmeCheckCommand(packagesDir))
     ..addCommand(TestCommand(packagesDir))
     ..addCommand(VersionCheckCommand(packagesDir))
     ..addCommand(XcodeAnalyzeCommand(packagesDir));

script/tool/lib/src/readme_check_command.dart

@@ -0,0 +1,152 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file/file.dart';
+import 'package:git/git.dart';
+import 'package:platform/platform.dart';
+import 'package:pubspec_parse/pubspec_parse.dart';
+import 'package:yaml/yaml.dart';
+
+import 'common/core.dart';
+import 'common/package_looping_command.dart';
+import 'common/process_runner.dart';
+import 'common/repository_package.dart';
+
+/// A command to enforce README conventions across the repository.
+class ReadmeCheckCommand extends PackageLoopingCommand {
+  /// Creates an instance of the README check command.
+  ReadmeCheckCommand(
+    Directory packagesDir, {
+    ProcessRunner processRunner = const ProcessRunner(),
+    Platform platform = const LocalPlatform(),
+    GitDir? gitDir,
+  }) : super(
+          packagesDir,
+          processRunner: processRunner,
+          platform: platform,
+          gitDir: gitDir,
+        );
+
+  // Standardized capitalizations for platforms that a plugin can support.
+  static const Map<String, String> _standardPlatformNames = <String, String>{
+    'android': 'Android',
+    'ios': 'iOS',
+    'linux': 'Linux',
+    'macos': 'macOS',
+    'web': 'Web',
+    'windows': 'Windows',
+  };
+
+  @override
+  final String name = 'readme-check';
+
+  @override
+  final String description =
+      'Checks that READMEs follow repository conventions.';
+
+  @override
+  bool get hasLongOutput => false;
+
+  @override
+  Future<PackageResult> runForPackage(RepositoryPackage package) async {
+    final File readme = package.readmeFile;
+
+    if (!readme.existsSync()) {
+      return PackageResult.fail(<String>['Missing README.md']);
+    }
+
+    final List<String> errors = <String>[];
+
+    final Pubspec pubspec = package.parsePubspec();
+    final bool isPlugin = pubspec.flutter?['plugin'] != null;
+
+    if (isPlugin && (!package.isFederated || package.isAppFacing)) {
+      final String? error = _validateSupportedPlatforms(package, pubspec);
+      if (error != null) {
+        errors.add(error);
+      }
+    }
+
+    return errors.isEmpty
+        ? PackageResult.success()
+        : PackageResult.fail(errors);
+  }
+
+  /// Validates that the plugin has a supported platforms table following the
+  /// expected format, returning an error string if any issues are found.
+  String? _validateSupportedPlatforms(
+      RepositoryPackage package, Pubspec pubspec) {
+    final List<String> contents = package.readmeFile.readAsLinesSync();
+
+    // Example table following expected format:
+    // |                | Android | iOS      | Web                    |
+    // |----------------|---------|----------|------------------------|
+    // | **Support**    | SDK 21+ | iOS 10+* | [See `camera_web `][1] |
+    final int detailsLineNumber =
+        contents.indexWhere((String line) => line.startsWith('| **Support**'));
+    if (detailsLineNumber == -1) {
+      return 'No OS support table found';
+    }
+    final int osLineNumber = detailsLineNumber - 2;
+    if (osLineNumber < 0 || !contents[osLineNumber].startsWith('|')) {
+      return 'OS support table does not have the expected header format';
+    }
+
+    // Utility method to convert an iterable of strings to a case-insensitive
+    // sorted, comma-separated string of its elements.
+    String sortedListString(Iterable<String> entries) {
+      final List<String> entryList = entries.toList();
+      entryList.sort(
+          (String a, String b) => a.toLowerCase().compareTo(b.toLowerCase()));
+      return entryList.join(', ');
+    }
+
+    // Validate that the supported OS lists match.
+    final dynamic platformsEntry = pubspec.flutter!['plugin']!['platforms'];
+    if (platformsEntry == null) {
+      logWarning('Plugin not support any platforms');
+      return null;
+    }
+    final YamlMap platformSupportMaps = platformsEntry as YamlMap;
+    final Set<String> actuallySupportedPlatform =
+        platformSupportMaps.keys.toSet().cast<String>();
+    final Iterable<String> documentedPlatforms = contents[osLineNumber]
+        .split('|')
+        .map((String entry) => entry.trim())
+        .where((String entry) => entry.isNotEmpty);
+    final Set<String> documentedPlatformsLowercase =
+        documentedPlatforms.map((String entry) => entry.toLowerCase()).toSet();
+    if (actuallySupportedPlatform.length != documentedPlatforms.length ||
+        actuallySupportedPlatform
+                .intersection(documentedPlatformsLowercase)
+                .length !=
+            actuallySupportedPlatform.length) {
+      printError('''
+${indentation}OS support table does not match supported platforms:
+${indentation * 2}Actual:     ${sortedListString(actuallySupportedPlatform)}
+${indentation * 2}Documented: ${sortedListString(documentedPlatformsLowercase)}
+''');
+      return 'Incorrect OS support table';
+    }
+
+    // Enforce a standard set of capitalizations for the OS headings.
+    final Iterable<String> incorrectCapitalizations = documentedPlatforms
+        .toSet()
+        .difference(_standardPlatformNames.values.toSet());
+    if (incorrectCapitalizations.isNotEmpty) {
+      final Iterable<String> expectedVersions = incorrectCapitalizations
+          .map((String name) => _standardPlatformNames[name.toLowerCase()]!);
+      printError('''
+${indentation}Incorrect OS capitalization: ${sortedListString(incorrectCapitalizations)}
+${indentation * 2}Please use standard capitalizations: ${sortedListString(expectedVersions)}
+''');
+      return 'Incorrect OS support formatting';
+    }
+
+    // TODO(stuartmorgan): Add validation that the minimums in the table are
+    // consistent with what the current implementations require. See
+    // https://github.com/flutter/flutter/issues/84200
+    return null;
+  }
+}