Microsoft/TypeScript
在 GitHub 查看Unexpected type infer for function first argument with default value since 5.1
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#57,706 建立於 2024年3月9日
Domain: check: Type InferenceHelp WantedPossible Improvement
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描述
🔎 Search Terms
"type infer first argument"
🕗 Version & Regression Information
- This is a crash
- This changed between versions v5.0.4 and v5.1.6
- This changed in commit or PR _______
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
- I was unable to test this on prior versions because _______
⏯ Playground Link
💻 Code
export type Factory<T> = (arg1: T, arg2: any) => any
export type Factory2<T> = (...args: [T, any]) => any
declare function infer1<T>(fn: Factory<T>): T
declare function infer2<T>(fn: Factory2<T>): T
const f1 = (msg: string = 'hello', test: any) => { }
const a1 = infer1(f1)
// ^? const a1: string | undefined
const a2 = infer2(f1)
// ^? const a2: string | undefined
const f2 = (msg: string = 'hello') => { }
const b = infer1(f2)
// ^? const b: string | undefined
const b1 = infer2(f2)
// ^? const b1: string | undefined
const c = infer1((msg: string = 'hello') => { })
// ^? const c: string
const c2 = infer2((msg: string = 'hello') => { })
// ^? const c2: string | undefined
🙁 Actual behavior
In my code you'll notice that the type of c is not the same as b, but the argument we passing into function infer1 is actually the same.
I've tested this between v5.0.4 and v5.1.6, but the type of c is different:
// v5.0.4
const c: string | undefined
// v5.1.6
const c: string
After checking v5.1 changelog, I'm still not sure what changes have been made between 5.0 to 5.1.
So I decided to submit this issue as a "Bug report".
🙂 Expected behavior
The type of c is supposed to be string | undefined.
Additional information about the issue
No response