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FRB Codegen

Working with flutter_rust_bridge code generation in Bull SDK.

When to Regenerate

Regenerate bindings when:

  • Modifying Rust API code in any sub-crate
  • Updating flutter_rust_bridge.yaml inputs
  • Adding new mirror types for data-variant enums
  • Upgrading flutter_rust_bridge version

Codegen Workflow

1. Run FRB Codegen

cd packages/bull_sdk
flutter_rust_bridge_codegen generate

This reads flutter_rust_bridge.yaml and generates: - lib/src/rust/frb_generated.dart — Dart bindings - rust/src/frb_generated.rs — Rust FFI dispatcher

2. Run Post-Processing (MANDATORY)

cd packages/bull_sdk
bash fix_frb_generated.sh

This patches rust/src/frb_generated.rs to: - Wrap external crate error types (LwkError, BoltzError) in FrbWrapper - Add .map_err(FrbWrapper) to closure results - Convert mirrored TxFee via .into() - Convert Vec<ArkTransaction> via iterator mapping

Never skip this step

Without fix_frb_generated.sh, the build fails with ~86 type errors.

3. Validate

cargo check -p rust_lib_bull_sdk

Should complete with zero errors.

Configuration

The codegen is configured in flutter_rust_bridge.yaml:

rust_input: crate::api, ark_wallet::ark, bbqr, dart_bbqr::api, boltz::api, lwk::api
rust_root: rust/
dart_output: lib/src/rust
dart_entrypoint_class_name: BullSdk
enable_lifetime: true
full_dep: true
dart3: true
web: false

Key Settings

Setting Value Meaning
rust_input Multiple crates Scans all sub-crate APIs
dart_entrypoint_class_name BullSdk Main init class
web false No WASM — Dart-only on web

Adding New Mirror Types

When a sub-crate exposes a data-variant enum, create a mirror in packages/bull_sdk/rust/src/api/simple.rs:

#[flutter_rust_bridge::frb(mirror(sub_crate::path::MyEnum))]
pub enum MyEnum {
    Variant1(u64),
    Variant2 { field: String },
}

impl From<MyEnum> for sub_crate::path::MyEnum { /* ... */ }
impl From<sub_crate::path::MyEnum> for MyEnum { /* ... */ }

Then re-run steps 1-3.

Platform Notes

  • macOS: fix_frb_generated.sh works as-is
  • Linux: Patch sed -i '' to sed -i before running (3 occurrences)
  • Windows: Use WSL or Git Bash