Refactor verifyVersion into typed Version object, use it (flutter#172780)

Towards flutter#171900.

Author: matanlurey

dev/bots/post_process_docs.dart

@@ -4,6 +4,7 @@
 
 import 'dart:convert';
 import 'dart:io';
+import 'package:file/local.dart';
 import 'package:intl/intl.dart';
 import 'package:meta/meta.dart';
 
@@ -12,6 +13,8 @@ import 'package:platform/platform.dart' as platform;
 
 import 'package:process/process.dart';
 
+import 'utils.dart';
+
 class CommandException implements Exception {}
 
 Future<void> main() async {
@@ -46,12 +49,15 @@ Future<void> postProcess() async {
 
   // Generate versions file.
   await runProcessWithValidations(<String>['flutter', '--version'], docsPath);
-  final File versionFile = File(path.join(checkoutPath, 'bin', 'cache', 'flutter.version.json'));
-  final String version = () {
-    final Map<String, Object?> json =
-        jsonDecode(versionFile.readAsStringSync()) as Map<String, Object?>;
-    return json['flutterVersion']! as String;
-  }();
+  final String version;
+  switch (await Version.resolveIn(const LocalFileSystem().directory(checkoutPath))) {
+    case VersionError(:final String error):
+      print('Could not read flutter version: $error');
+      exit(1);
+    case VersionOk(version: final String parsedVersion):
+      version = parsedVersion;
+  }
+
   // Recreate footer
   final String publishPath = path.join(docsPath, '..', 'docs', 'doc', 'flutter', 'footer.js');
   final File footerFile = File(publishPath)..createSync(recursive: true);

dev/bots/suite_runners/run_test_harness_tests.dart

@@ -128,9 +128,8 @@ Future<void> testHarnessTestsRunner() async {
   }
 
   // Verify that we correctly generated the version file.
-  final String? versionError = await verifyVersion(File(path.join(flutterRoot, 'version')));
-  if (versionError != null) {
-    foundError(<String>[versionError]);
+  if (await Version.resolveIn() case final VersionError e) {
+    foundError(<String>[e.error]);
   }
 }
 

dev/bots/test/test_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:convert';
 import 'dart:io' hide Platform;
 
 import 'package:collection/collection.dart';
@@ -50,12 +51,12 @@ void main() {
         '1.2.3-5.0.pre.12',
       ];
       for (final String version in valid_versions) {
-        final File file = fileSystem.file('version');
-        file.writeAsStringSync(version);
+        final fs.File file = fileSystem.file('version');
+        file.writeAsStringSync(jsonEncode(<String, String>{'flutterVersion': version}));
 
-        expect(
-          await verifyVersion(file),
-          isNull,
+        await expectLater(
+          Version.resolveFile(file),
+          completion(isA<VersionOk>()),
           reason: '$version is valid but verifyVersionFile said it was bad',
         );
       }
@@ -72,12 +73,18 @@ void main() {
         '1.2.3-hotfix.1',
       ];
       for (final String version in invalid_versions) {
-        final File file = fileSystem.file('version');
-        file.writeAsStringSync(version);
-
-        expect(
-          await verifyVersion(file),
-          'The version logic generated an invalid version string: "$version".',
+        final fs.File file = fileSystem.file('version');
+        file.writeAsStringSync(jsonEncode(<String, String>{'flutterVersion': version}));
+
+        await expectLater(
+          Version.resolveFile(file),
+          completion(
+            isA<VersionError>().having(
+              (VersionError e) => e.error,
+              'error',
+              'The version logic generated an invalid version string: "$version".',
+            ),
+          ),
           reason: '$version is invalid but verifyVersionFile said it was fine',
         );
       }

dev/bots/utils.dart

@@ -735,22 +735,75 @@ Future<void> _runFromList(
   }
 }
 
-/// Checks the given file's contents to determine if they match the allowed
-/// pattern for version strings.
-///
-/// Returns null if the contents are good. Returns a string if they are bad.
-/// The string is an error message.
-Future<String?> verifyVersion(File file) async {
-  final RegExp pattern = RegExp(r'^(\d+)\.(\d+)\.(\d+)((-\d+\.\d+)?\.pre([-\.]\d+)?)?$');
-  if (!file.existsSync()) {
-    return 'The version logic failed to create the Flutter version file.';
-  }
-  final String version = await file.readAsString();
-  if (version == '0.0.0-unknown') {
-    return 'The version logic failed to determine the Flutter version.';
+/// Provides access to read and parse the `bin/cache/flutter.version.json`.
+sealed class Version {
+  static final RegExp _pattern = RegExp(r'^(\d+)\.(\d+)\.(\d+)((-\d+\.\d+)?\.pre([-\.]\d+)?)?$');
+
+  /// Attempts to read and resolve the version stored in the [checkoutPath].
+  ///
+  /// If omitted, defaults the current flutter root using the real file system.
+  static Future<Version> resolveIn([fs.Directory? checkoutPath]) async {
+    checkoutPath ??= const LocalFileSystem().directory(flutterRoot);
+    return resolveFile(
+      checkoutPath.childDirectory('bin').childDirectory('cache').childFile('flutter.version.json'),
+    );
+  }
+
+  /// Attempts to read and resolve the version stored in [file].
+  static Future<Version> resolveFile(fs.File file) async {
+    if (!file.existsSync()) {
+      return VersionError._(
+        'The version logic failed to create the Flutter version file: ${file.path}',
+        contents: null,
+      );
+    }
+    final Object? json = jsonDecode(await file.readAsString());
+    if (json is! Map<String, Object?>) {
+      return VersionError._('The version file was in an unexpected format.', contents: '$json');
+    }
+    final String? version = json['flutterVersion'] as String?;
+    if (version == null) {
+      return VersionError._(
+        'The version file was missing the key "flutterVersion".',
+        contents: '$json',
+      );
+    }
+    if (version == '0.0.0-unknown') {
+      return VersionError._(
+        'The version logic failed to determine the Flutter version.',
+        contents: version,
+      );
+    }
+    if (!version.contains(_pattern)) {
+      return VersionError._(
+        'The version logic generated an invalid version string: "$version".',
+        contents: version,
+      );
+    }
+    return VersionOk._(version);
   }
-  if (!version.contains(pattern)) {
-    return 'The version logic generated an invalid version string: "$version".';
+}
+
+/// A failed result of [Version.resolveFile].
+final class VersionError implements Version {
+  const VersionError._(this.error, {required this.contents});
+
+  /// Describes the error state.
+  final String error;
+
+  /// The contents of the version file, if any.
+  final String? contents;
+
+  @override
+  String toString() {
+    return error;
   }
-  return null;
+}
+
+/// A successful result of [Version.resolveFile].
+final class VersionOk implements Version {
+  const VersionOk._(this.version);
+
+  /// The contents of the version file, successfully parsed.
+  final String version;
 }