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Invalid declaration emit for conditional type with 'infer' #22755
Description
TypeScript Version: 2.8.0-rc
Search Terms: "invalid declaration emit", "declaration infer"
Code
// ========== tsc input ==========
// index.ts
// @declaration: true
export declare function foo<T>(obj: T): T extends () => infer P ? P : never;
export function bar<T>(obj: T) {
return foo(obj);
}
// ========== tsc output ==========
// index.d.ts
export declare function foo<T>(obj: T): T extends () => infer P ? P : never;
export declare function bar<T>(obj: T): T extends () => P ? P : never;Expected behavior:
In the emitted declaration file, foo and bar should have equivalent return type annotations.
Actual behavior:
The return type annotation for bar is missing the infer keyword, making the declaration invalid. Any TypeScript project consuming this declaration file will produce the error "Cannot find name 'P'".
Related Issues:
- 'infer' type parameters declarations aren't printed in quick info. #21836 is similar but relates to Quick Info. The sample code there produces a correct declaration emit however.
- WIP - Allow infer types in expression type argument positions #22368 says it fixes 'infer' type parameters declarations aren't printed in quick info. #21836, so maybe it fixes this too?
Activity
yortus commentedon Mar 21, 2018
Wesley Wigham (@weswigham) would #22368 fix this?
weswigham commentedon Mar 21, 2018
It might, by chance, because I introduced an actual
InferTypetype kind in that PR so I could distinguish the infer location from the use locations for type parameter lists.DanielRosenwasser commentedon Mar 21, 2018
Let's get a fix specifically for this first if we can, and then use #22368 if that gets pulled in.