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Compiler hangs #31823
Description
But looks like CPU and Memory usage is not increasing.
TypeScript Version: master
Search Terms:
Code
export type Prepend<Elm, T extends unknown[]> =
T extends unknown ?
((arg: Elm, ...rest: T) => void) extends ((...args: infer T2) => void) ? T2 :
never :
never;
export type ExactExtract<T, U> = T extends U ? U extends T ? T : never : never;
type Conv<T, U = T> =
{ 0: [T]; 1: Prepend<T, Conv<ExactExtract<U, T>>>;}[U extends T ? 0 : 1];Expected behavior:
pass
Actual behavior:
hang
Playground Link:
Related Issues:
Activity
sandersn commentedon Jun 11, 2019
Also fails on 3.5.1
weswigham commentedon Jun 12, 2019
The type expands so well:
I'm actually surprised we just hang rather than quickly OOM. Apparently a
Conv<ExactExtract<U, T>>is not a simple type, and determining if it's assignable to anunknown[]is not so easy. :Pfatcerberus commentedon Jun 26, 2019
Wesley Wigham (@weswigham) Wait, why does that type expand recursively like that? Shouldn't that have been caught by the instantiation depth limiter?
weswigham commentedon Jun 26, 2019
Oh, it is. The depth limit is 50 instances of the same type and there's like 10 different types, so that's like 500 types deep that it can easily go.