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Possible 4.3 regression with generic function and rest in object destructuring #43941
Description
Bug Report
🔎 Search Terms
🕗 Version & Regression Information
- This changed between versions 4.2 and 4.3 beta
⏯ Playground Link
Playground link with relevant code
💻 Code
type Params = {
foo: string;
} & ({ tag: 'a'; type: number } | { tag: 'b'; type: string });
const getType = <P extends Params>(params: P) => {
const {
// Omit
foo,
...rest
} = params;
return rest;
};
declare const params: Params;
switch (params.tag) {
case 'a': {
// TS 4.2: number
// TS 4.3: string | number
const result = getType(params).type;
break;
}
case 'b': {
// TS 4.2: string
// TS 4.3: string | number
const result = getType(params).type;
break;
}
}🙁 Actual behavior
4.3 behaviour should match 4.2 behaviour. See comments in code.
🙂 Expected behavior
See comments in code.
Activity
OliverJAsh commentedon May 27, 2021
This is marked as fixed but the behaviour in 4.3.2 still differs from 4.2 as per my comment above. Is that expected?
OliverJAsh commentedon May 31, 2021
Wesley Wigham (@weswigham) Not sure this issue has been fixed, should we re-open it?
weswigham commentedon Jun 1, 2021
It definitely looks fixed in the nightly playground... and in the associated PR's tests...
OliverJAsh commentedon Jun 2, 2021
I had a look at the tests but I couldn't understand what behaviour they were trying to verify. Do we expect my example to behave the same in 4.3 as it did in 4.2, or is this an intended change? In my testing the behaviour in 4.3 and nightly differs from that of 4.2, as per my code comments.
weswigham commentedon Jun 2, 2021
I see the behavior match what you noted as the 4.2 behavior in the nightly playground?
OliverJAsh commentedon Jun 2, 2021
Yes you're right, sorry!