Regression in 7.1: contextual parameter type is lost for a destructuring pattern with a default (TS7031) #65011

🔎 Search Terms

TS7031, implicit any, destructuring parameter, default value, JSDoc returns, checkJs, contextual typing

🕗 Version & Regression Information

• This is a regression. It works in tsc 5.9.3 and in 7.0.2, and fails from 7.1 onwards:

The Go implementation from that commit (tsc inside typescript@7.1.0-beta) behaves the same, so this is not specific to one host.

💻 Code

A checkJs file. The object literal is contextually typed by a JSDoc @returns; the method's second parameter is a destructuring pattern with a default.

tsconfig.json:

{ "compilerOptions": { "strict": true, "noEmit": true, "allowJs": true, "checkJs": true, "target": "es2022" }, "files": ["a.js"] }

a.js:

/** @typedef {{ signal?: AbortSignal }} Opts */
/** @typedef {{ structure: (c: string, o?: Opts) => Promise<string[]> }} Adapter */
/** @returns {Adapter} */
export function make() {
  return {
    async structure(c, { signal } = {}) {
      signal?.throwIfAborted()
      return [c]
    },
  }
}

The same happens when the function is a cast target rather than a returned object member:

/** @typedef {(n: number, o?: Opts) => Promise<void>} Fn */
export const p = /** @type {Fn} */ (async (n, { signal } = {}) => {
  signal?.throwIfAborted()
})

🙁 Actual behavior

a.js(6,26): error TS7031: Binding element 'signal' implicitly has an 'any' type.

🙂 Expected behavior

No error: signal is typed AbortSignal | undefined from the contextual Opts, as in 5.9 and 7.0.

Notes

• Destructuring is not generally broken. Removing the = {} default keeps it working, and so does taking a named parameter and destructuring it in the body:

  async structure(c, opts) { const { signal } = opts ?? {}; signal?.throwIfAborted(); return [c] }

• Tagging the parameters explicitly makes 7.1 accept the method again, so a workaround exists for callers who hit it:

  /** @param {string} c @param {Opts} [o] */
  async structure(c, { signal } = {}) { … }

• Not specific to JavaScript or JSDoc. The same shape in .ts fails too:

  type O = { signal?: AbortSignal }
  const f: (o?: O) => void = ({ signal } = {}) => { signal?.throwIfAborted() }

  7.1.0-beta reports TS7031 here; 5.9.3 and 7.0.2 do not.
• Found in a checkJs library that needed it on seven methods. Reported through a port that quotes this compiler against the pinned commit, JS: destructured parameter loses contextual typing from a JSDoc @returns type and reports TS7031 oxc-project/tsrs#847.