FRB Develop Feature

Note: Check your user-level remote-testing rules before running commands. Tests and codegen may require remote execution.

Overview

Iterate in frb_example/dart_minimal (fast compile), migrate to frb_example/pure_dart (full coverage).

Write one test → get ~6 variants automatically via TwinNormal suffix.

When to Use

• •Adding a new function or feature
• •Writing tests for new or existing functionality
• •Compilation feels slow (use frb_example/dart_minimal instead)

Implementation

digraph workflow {
    rankdir=TB;
    node [shape=box];

    "Write test + impl in dart_minimal" -> "Run test";
    "Run test" -> "Pass?" [shape=diamond];
    "Pass?" -> "Move to pure_dart" [label="yes"];
    "Pass?" -> "Fix" [label="no"];
    "Fix" -> "Run test";
    "Move to pure_dart" -> "Add TwinNormal suffix" -> "Run code gen" -> "All tests pass?";
    "All tests pass?" -> "Done" [label="yes"];
    "All tests pass?" -> "Debug" [label="no"];
    "Debug" -> "All tests pass?";
}

Phase 1: Iterate in frb_example/dart_minimal

1. •

   Add tests:

   • •Rust: add function to frb_example/dart_minimal/rust/src/api/minimal.rs
   • •Dart: add test to frb_example/dart_minimal/test/minimal_test.dart

   There is usually no need to create any new files.

2. •

   Add implementations:

   Usually need to modify frb_codegen, frb_dart, and/or frb_rust.

3. •

   Run codegen and test:

   bash

   (cd frb_example/dart_minimal && cargo run --manifest-path ../../frb_codegen/Cargo.toml -- generate)
   ./frb_internal test-dart-native --package frb_example/dart_minimal
   

   After codegen: Check your user-level remote-testing rules. If codegen was run remotely, pull changes back to local.

4. •

   Iterate until test passes

Phase 2: Migrate to frb_example/pure_dart

1. •

   Move code to frb_example/pure_dart:

   • •Rust: frb_example/pure_dart/rust/src/api/my_feature.rs
   • •Dart: frb_example/pure_dart/test/api/my_feature_test.dart

   Either add to existing files or create new files. Then remove from frb_example/dart_minimal files.

2. •

   Add TwinNormal suffix to all functions and types:

   Context	Suffix	Example
   snake_case	_twin_normal	my_func_twin_normal()
   PascalCase	TwinNormal	MyStructTwinNormal

   This triggers automatic test generation (~6 variants) under different codegen modes. Always mimic existing frb_example/pure_dart tests for exact patterns.

3. •

   Run codegen and test:

   bash

   # Codegen
   ./frb_internal precommit-generate
   
   # Native tests (can run in parallel)
   ./frb_internal test-dart-native --package frb_example/pure_dart
   ./frb_internal test-dart-native --package frb_example/pure_dart_pde
   
   # Web tests (optional, for web platform coverage)
   ./frb_internal test-dart-web --package frb_example/pure_dart
   ./frb_internal test-dart-web --package frb_example/pure_dart_pde
   

   After codegen: Check your user-level remote-testing rules. If codegen was run remotely, pull changes back to local.

   Native tests must pass - they test different codegen configurations. Web tests are optional but recommended for web platform coverage.

4. •

   Iterate until test passes

   You may use frb_example/dart_minimal again if there are bugs and need fast iteration.

Quick Reference

Tasks and Commands

Architecture

• •Doc: website/docs/guides/contributing/overview.md - System architecture, codegen flow, directory structure
• •Key directories:

  Directory	Purpose
  frb_codegen/	Code generator (IR → Rust/Dart output)
  frb_dart/	Dart runtime library
  frb_rust/	Rust runtime library
  frb_example/	Examples + tests (pure_dart has most coverage)

Common Mistakes

Related Skills

• •frb-code-generation - Which generation commands to run
• •frb-test - How to run tests locally
• •frb-debugging - Debug code generation issues
• •frb-prepare-pr - Preparing a PR for review