feat: Rollback on failed shared dependency resolution (#848)

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## Description

Fixed: #847 

## Type of Change

<!--- Put an `x` in all the boxes that apply: -->

- [x] ✨ `feat` -- New feature (non-breaking change which adds
functionality)
- [ ] 🛠️ `fix` -- Bug fix (non-breaking change which fixes an issue)
- [ ] ❌ `!` -- Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] 🧹 `refactor` -- Code refactor
- [ ] ✅ `ci` -- Build configuration change
- [ ] 📝 `docs` -- Documentation
- [ ] 🗑️ `chore` -- Chore

packages/melos/lib/src/commands/bootstrap.dart

@@ -37,25 +37,29 @@ mixin _BootstrapMixin on _CleanMixin {
           ..newLine();
 
         final filteredPackages = workspace.filteredPackages.values;
+        final rollbackPubspecContent = <String, String>{};
 
         try {
           if (bootstrapCommandConfig.environment != null ||
               bootstrapCommandConfig.dependencies != null ||
               bootstrapCommandConfig.devDependencies != null) {
             logger.log('Updating common dependencies in workspace packages...');
 
-            await Stream.fromIterable(filteredPackages).parallel((package) {
+            await Stream.fromIterable(filteredPackages)
+                .parallel((package) async {
+              final pubspecPath = utils.pubspecPathForDirectory(package.path);
+              final pubspecContent = await readTextFileAsync(pubspecPath);
+              rollbackPubspecContent[pubspecPath] = pubspecContent;
+
               return _setSharedDependenciesForPackage(
                 package,
+                pubspecPath: pubspecPath,
+                pubspecContent: pubspecContent,
                 environment: bootstrapCommandConfig.environment,
                 dependencies: bootstrapCommandConfig.dependencies,
                 devDependencies: bootstrapCommandConfig.devDependencies,
               );
             }).drain<void>();
-
-            logger
-              ..child(successLabel, prefix: '> ')
-              ..newLine();
           }
 
           logger.log(
@@ -73,6 +77,18 @@ mixin _BootstrapMixin on _CleanMixin {
             ..child(successLabel, prefix: '> ')
             ..newLine();
         } on BootstrapException catch (exception) {
+          if (rollbackPubspecContent.isNotEmpty) {
+            logger.log(
+              'Dependency resolution failed, rolling back changes to '
+              'the pubspec.yaml files...',
+            );
+
+            await Stream.fromIterable(rollbackPubspecContent.entries)
+                .parallel((entry) async {
+              await writeTextFileAsync(entry.key, entry.value);
+            }).drain<void>();
+          }
+
           _logBootstrapException(exception, workspace);
           rethrow;
         }
@@ -175,13 +191,13 @@ mixin _BootstrapMixin on _CleanMixin {
 
   Future<void> _setSharedDependenciesForPackage(
     Package package, {
+    required String pubspecPath,
+    required String pubspecContent,
     required Map<String, VersionConstraint?>? environment,
     required Map<String, Dependency>? dependencies,
     required Map<String, Dependency>? devDependencies,
   }) async {
-    final packagePubspecFile = utils.pubspecPathForDirectory(package.path);
-    final packagePubspecContents = await readTextFileAsync(packagePubspecFile);
-    final pubspecEditor = YamlEditor(packagePubspecContents);
+    final pubspecEditor = YamlEditor(pubspecContent);
 
     final updatedEnvironment = _updateEnvironment(
       pubspecEditor: pubspecEditor,
@@ -204,10 +220,7 @@ mixin _BootstrapMixin on _CleanMixin {
     );
 
     if (pubspecEditor.edits.isNotEmpty) {
-      await writeTextFileAsync(
-        packagePubspecFile,
-        pubspecEditor.toString(),
-      );
+      await writeTextFileAsync(pubspecPath, pubspecEditor.toString());
 
       final message = <String>[
         if (updatedEnvironment) 'Updated environment',

packages/melos/test/commands/bootstrap_test.dart

@@ -946,6 +946,139 @@ Generating IntelliJ IDE files...
     });
   });
 
+  test(
+    'rollbacks applied shared dependencies on resolution failure',
+    () async {
+      final workspaceDir = await createTemporaryWorkspace(
+        workspacePackages: ['a', 'b'],
+        configBuilder: (path) => MelosWorkspaceConfig(
+          name: 'Melos',
+          packages: [
+            createGlob('packages/**', currentDirectoryPath: path),
+          ],
+          commands: CommandConfigs(
+            bootstrap: BootstrapCommandConfigs(
+              environment: {
+                'sdk': VersionConstraint.parse('>=3.6.0 <4.0.0'),
+                'flutter': VersionConstraint.parse('>=2.18.0 <3.0.0'),
+              },
+              dependencies: {
+                'flame': HostedDependency(
+                  version: VersionConstraint.compatibleWith(
+                    // Should fail since the version is not compatible with
+                    // the flutter version.
+                    Version.parse('0.1.0'),
+                  ),
+                ),
+              },
+              devDependencies: {
+                'flame_lint': HostedDependency(
+                  version: VersionConstraint.compatibleWith(
+                    Version.parse('1.2.1'),
+                  ),
+                ),
+              },
+            ),
+          ),
+          path: path,
+        ),
+      );
+
+      final pkgA = await createProject(
+        workspaceDir,
+        Pubspec(
+          'a',
+          environment: {},
+          dependencies: {
+            'flame': HostedDependency(
+              version:
+                  VersionConstraint.compatibleWith(Version.parse('1.23.0')),
+            ),
+          },
+          devDependencies: {
+            'flame_lint': HostedDependency(
+              version: VersionConstraint.compatibleWith(Version.parse('1.2.0')),
+            ),
+          },
+        ),
+      );
+
+      final pkgB = await createProject(
+        workspaceDir,
+        Pubspec(
+          'b',
+          environment: {
+            'sdk': VersionConstraint.parse('>=2.12.0 <3.0.0'),
+            'flutter': VersionConstraint.parse('>=2.12.0 <3.0.0'),
+          },
+          dependencies: {
+            'flame': HostedDependency(
+              version:
+                  VersionConstraint.compatibleWith(Version.parse('1.23.0')),
+            ),
+            'integral_isolates': HostedDependency(
+              version: VersionConstraint.compatibleWith(Version.parse('0.4.1')),
+            ),
+            'intl': HostedDependency(
+              version:
+                  VersionConstraint.compatibleWith(Version.parse('0.17.0')),
+            ),
+            'path': HostedDependency(version: VersionConstraint.any),
+          },
+        ),
+      );
+
+      final logger = TestLogger();
+      final config = await MelosWorkspaceConfig.fromWorkspaceRoot(workspaceDir);
+      final melos = Melos(
+        logger: logger,
+        config: config,
+      );
+
+      final pubspecAPreBootstrap = pubspecFromYamlFile(directory: pkgA.path);
+      final pubspecBPreBootstrap = pubspecFromYamlFile(directory: pkgB.path);
+
+      await expectLater(
+        () => runMelosBootstrap(melos, logger),
+        throwsA(isA<BootstrapException>()),
+      );
+
+      final pubspecA = pubspecFromYamlFile(directory: pkgA.path);
+      final pubspecB = pubspecFromYamlFile(directory: pkgB.path);
+
+      expect(
+        pubspecAPreBootstrap.environment,
+        equals(defaultTestEnvironment),
+      );
+      expect(
+        pubspecA.environment['sdk'],
+        equals(pubspecAPreBootstrap.environment['sdk']),
+      );
+      expect(
+        pubspecA.dependencies,
+        equals(pubspecAPreBootstrap.dependencies),
+      );
+      expect(
+        pubspecA.devDependencies,
+        equals(pubspecAPreBootstrap.devDependencies),
+      );
+
+      expect(
+        pubspecBPreBootstrap.environment['flutter'],
+        equals(VersionConstraint.parse('>=2.12.0 <3.0.0')),
+      );
+      expect(
+        pubspecB.dependencies,
+        equals(pubspecBPreBootstrap.dependencies),
+      );
+      expect(
+        pubspecB.devDependencies,
+        equals(pubspecBPreBootstrap.devDependencies),
+      );
+    },
+    timeout: const Timeout(Duration(minutes: 20)),
+  );
+
   group('melos bs --offline', () {
     test('should run pub get with --offline', () async {
       final workspaceDir = await createTemporaryWorkspace(