¶Codegen — specta → TypeScript

rata codegen generates a bindings.ts from your commands, containing:

1. TypeScript type declarations for every referenced Rust type, and
2. a typed api.* facade whose calls delegate to @elyra/runtime's invoke.

It uses specta for the type graph and specta-typescript's framework_runtime hook (the same mechanism tauri-specta uses) — but Elyra has its own bridge, so rata codegen is the replacement for tauri-specta's generator.

¶Running it

rata codegen        # writes to [codegen].out (default app/src/bindings.ts)

Under the hood the app runs in codegen mode (ELYRA_CODEGEN_OUT is set), writes the file, and exits before opening a window.

¶Example output

// Generated by Ratatosk (`rata codegen`). Do not edit by hand.
import { invoke } from "@elyra/runtime";

export type Todo = { id: number, title: string, done: boolean };

export const api = {
  greet(name: string): Promise<string> {
    return invoke("greet", name);
  },
  list_todos(): Promise<Todo[]> {
    return invoke("list_todos");
  },
  checked_div(a: number, b: number): Promise<number> {
    return invoke("checked_div", a, b);
  },
};

• Named types render as references (Promise<Todo>), not inlined.
• Result<T, E> commands surface T; errors reject the promise.
• Every command arg/return type must implement specta::Type (and serde).

¶serde attributes

Types are exported through specta-serde, so serde container attributes are reflected in the generated TypeScript:

• #[serde(rename = "...")] / #[serde(rename_all = "...")] — field and variant renaming.
• Tagged enums (#[serde(tag = "...")], tag + content, untagged) — rendered as discriminated (or bare) unions.
• #[serde(flatten)] — merged as a TypeScript intersection (A & B).
• #[serde(skip)] / skip_serializing — omitted fields.

Keep serde symmetric (the same shape for serialize and deserialize); asymmetric attributes aren't supported by this single-shape export.

¶Number policy

The sqlx/JS number story has sharp edges; Elyra's policy (in codegen.rs):

• specta-typescript refuses to export 64-bit integers (they can't round-trip through a JS number). Elyra's wire is MessagePack, where they already arrive as JS numbers, so i64/u64/… render as number.
• Floats render as number (not specta's JSON-oriented number | null) — MessagePack represents NaN/Infinity natively.
• This applies both to the facade and to named-struct fields (a collection-level pass), so a struct with an i64 field exports cleanly.

If you need integers beyond 2^53, reach for bigint transport (a future opt-in).

¶Related

• Frontend runtime — using api.*
• Commands · Models (models are plain structs, so they flow through codegen)