melbournedeveloper/dart_sdk_skills/modify-dart-language

Modifying the Dart Language

Compiler pipeline

Source → _fe_analyzer_shared (scan+parse) → front_end (type-check) → kernel IR
                                                    ↓
              ┌─────────────────────────────────────┼───────────────────┐
              ↓                                     ↓                   ↓
    pkg/compiler (dart2js)              runtime/vm/compiler      pkg/dart2wasm
    → JavaScript                        → native code            → WebAssembly

All backends share the same front-end. Language changes typically touch:

1. Parser (pkg/_fe_analyzer_shared/)
2. CFE type inference (pkg/front_end/)
3. Analyzer AST (pkg/analyzer/)
4. Tests (tests/language/)

Key files by subsystem

Adding an experimental feature

1. Add entry to tools/experimental_features.yaml:

``yaml my-feature: help: "Short description of the feature." ``

1. Regenerate flags:

``bash ./tools/sdks/dart-sdk/bin/dart pkg/front_end/tool/cfe.dart generate-experimental-flags ``

1. Gate parser/CFE code with the experiment flag.

Subsystem reference docs

• Analyzer AST patterns: ast-patterns.md — adding AST nodes, visitor methods
• CFE patterns: cfe-patterns.md — body builder, diagnostics, Kernel IR
• Parser patterns: parser-patterns.md — parser methods, listener events

Code generation steps

After modifying AST nodes or messages, run the appropriate generators:

# After editing messages.yaml
./tools/sdks/dart-sdk/bin/dart pkg/front_end/tool/generate_messages.dart
 
# After editing experimental_features.yaml
./tools/sdks/dart-sdk/bin/dart pkg/front_end/tool/cfe.dart generate-experimental-flags
 
# After editing analyzer AST (regenerate visitors etc.)
./tools/sdks/dart-sdk/bin/dart pkg/analyzer/tool/generate_nodes.dart
 
# After editing parser tests
./tools/sdks/dart-sdk/bin/dart pkg/front_end/tool/update_expectations.dart

Typical feature implementation order

1. Add experimental flag
2. Parser changes (scan, parse, listener events)
3. CFE changes (body builder, type inference, Kernel IR generation)
4. Analyzer AST changes (nodes, visitors, resolution)
5. Diagnostic messages
6. Language tests
7. Update static error test expectations