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Unable to read properties off object spread in generic function parameter (regression with 4.6.1-rc) #47865
Description
Bug Report
I noticed a regression between TypeScript 4.6.0-beta and 4.6.1-rc in my repo where parameters to generic functions that use object spread sometimes get an unusable type.
🔎 Search Terms
- object spread
- 4.6.1-rc
🕗 Version & Regression Information
- This changed between versions 4.6.0-beta and 4.6.1-rc.
⏯ Playground Link
Playground link with relevant code
💻 Code
(see comment below for a simpler repro: #47865 (comment))
/** Extract params from an express path (e.g. '/students/:studentId'). */
export type ExtractRouteParams<T extends string> = string extends T
? Record<string, string>
: T extends `${infer _Start}:${infer Param}/${infer Rest}`
? {[k in Param | keyof ExtractRouteParams<Rest>]: string}
: T extends `${infer _Start}:${infer Param}`
? {[k in Param]: string}
: {};
declare function get<T extends string>(
path: T,
handler: (params: ExtractRouteParams<T>) => void,
): void;
get('/path/:foo/to/:bar', ({foo, ...slugs}) => {
const {bar} = slugs; // ok in TS 4.6.0-beta but not in TS 4.6.1-rc
console.log({bar});
});
get('/path/:foo/to/:bar', slugs => {
const {bar} = slugs; // ok in both
console.log({bar});
});🙁 Actual behavior
Using object spread in a function parameter produces an unusable type in TS 4.6.1-rc.
The type of slugs in the first example is:
slugs: { bar: string; }
in TypeScript 4.6.0-beta but:
slugs: Omit<ExtractRouteParams<T>, "foo">
in TypeScript 4.6.1-rc.
These are both the same (assuming T = "/path/:foo/to/:bar") but the latter doesn't let me read any properties off of it.
🙂 Expected behavior
I should be able to read bar off of slugs.
Activity
danvk commentedon Feb 14, 2022
Here's a simpler repro that doesn't involve template literal types. This (correctly) passes the type checker with TS 4.5.5 but raises a spurious error with 4.6.1-rc.
RyanCavanaugh commentedon Feb 14, 2022
Bisected to #47337
RyanCavanaugh commentedon Feb 14, 2022
Gabriela Araujo Britto (@gabritto) seems like we're failing to assign the inferred type to
resthere;Tshouldn't be appearing at all