Fixes flutter#99153 ## Summary # Flutter Issue Investigation: flutter#99153 **Issue**: [flutter#99153 - Use dependency graph to determine plugin initialization order](flutter#99153) **Status**: Resolved **Scope**: `packages/flutter_tools` --- ## 1. Overview and Problem Statement When Flutter generates native plugin registrants (such as `GeneratedPluginRegistrant.java`, `GeneratedPluginRegistrant.m`, `generated_plugin_registrant.cc`, `web_plugin_registrant.dart`) and plugin dependency files (`.flutter-plugins-dependencies`), plugins were previously sorted purely alphabetically by plugin name (`left.name.compareTo(right.name)`). While alphabetical sorting ensured deterministic registrant generation, it did not take into account dependencies between plugins. If `plugin_a` depended on `plugin_z`, `plugin_a` would be registered and initialized before `plugin_z`, leading to potential initialization order bugs when a plugin depends on services or state initialized by another plugin. --- ## 2. Root Cause Analysis 1. **`findPlugins` & `refreshPluginsList`**: - `findPlugins` collected plugins in arbitrary traversal order from `computeTransitiveDependencies`. - `refreshPluginsList` sorted `plugins` alphabetically (`plugins.sort((Plugin left, Plugin right) => left.name.compareTo(right.name));`). 2. **`_resolvePluginImplementationsByPlatform`**: - Platform implementation candidate resolution re-sorted the platform-specific plugins alphabetically (`pluginImplementations.sort((Plugin left, Plugin right) => left.name.compareTo(right.name));`), overriding any topological order. 3. **`_writeFlutterPluginsList` and Registrant Generators**: - Iterated over the sorted lists and wrote registrations directly to disk. --- ## 3. Solution & Architecture ### Topological Sort (`sortByDependencies`) Implemented `sortByDependencies(Iterable<Plugin> plugins)` in `packages/flutter_tools/lib/src/flutter_plugins.dart`: - Uses Kahn's algorithm for topological sorting: 1. Computes in-degree for all plugins within the set of active plugins based on `plugin.dependencies`. Non-plugin dependencies (e.g., `flutter`, `meta`, external packages) are filtered out. 2. Seeds available queue with plugins having 0 in-degree, sorted alphabetically. 3. Dequeues plugins and decrements dependent plugins' in-degrees. When in-degree reaches 0, dependent plugins are added to the available queue (alphabetically sorted). 4. If a dependency cycle occurs, the algorithm breaks cycles deterministically by selecting the unplaced plugin with the smallest in-degree, breaking ties alphabetically. 5. For independent plugins with no dependency relationships, preserves alphabetical sorting. ### Call Site Updates - Updated `findPlugins` to return `sortByDependencies(plugins)`. - Updated `_resolvePluginImplementationsByPlatform` to sort platform implementations using `sortByDependencies(pluginResolution.values)`. - Removed redundant `plugins.sort` in `refreshPluginsList` and `packages/flutter_tools/lib/src/commands/build_swift_package.dart`. --- ## 4. Automated Testing and Verification ### Regression & Unit Tests Added - **`Refreshing the plugin list sorts plugins by dependency order`** in `packages/flutter_tools/test/general.shard/plugins_test.dart`. - **`group('sortByDependencies')`** in `plugins_test.dart`: - `returns empty list when input is empty` - `returns single element list as-is` - `sorts independent plugins alphabetically` - `sorts direct dependency before dependent plugin` - `sorts multi-level linear dependency chain` - `sorts diamond dependency graph` - `ignores non-plugin dependencies` - `handles dependency cycle deterministically without throwing or hanging` - **Registrant Injection Tests**: - `Generated Linux plugin files sorts by dependency order` - `Generated Windows plugin files sorts by dependency order` ### Verification Results - `dart format` cleanly applied across all modified files. - `dart analyze --fatal-infos packages/flutter_tools`: Passed with **0 errors, 0 warnings, 0 infos**. - `dart test packages/flutter_tools/test/general.shard/plugins_test.dart`: All **97 tests passing**. ## Verification - Regression test included and verified.

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