[Bug]tsc does not finish

[kgtkr]

TypeScript Version: 3.0.1/3.1.0-dev.20180808

Search Terms:

Code

type Head<T> = T extends [infer P, ...any[]] ? P : never;
type Tail<L extends any[]> = ((...x: L) => void) extends ((h: any, ...rest: infer T) => void) ? T : never

type Last<T extends any[]> = {
 0: never,
 1: Head<T>,
 2: Last<Tail<T>>,
}[T extends [] ? 0 : T extends [any] ? 1 : 2];

type Reverse<L extends any[], X extends any[]=[]> = {
 1: X, 0: Reverse<Tail<L>, Cons<Head<L>, X>>
}[L extends [] ? 1 : 0]

type Fn<R extends any[]> = (...args: R) => void
type Fn1<H, T extends any[]> = (h: H, ...args: T) => void
type Cons<H, T extends any[]> = Fn1<H, T> extends Fn<infer R> ? R : []

type Zip<A extends any[], B extends any[], R extends any[]=[]> = {
 0: Reverse<R>,
 1: Zip<Tail<A>, Tail<B>, Cons<[Head<A>, Head<B>], R>>
}[A extends [] ? 0 : B extends [] ? 0 : 1];

type ShiftZip<T extends any[]> = Zip<T, Tail<T>>;

type Tuple2Fn<T> = T extends [infer A, infer B] ? (x: A) => B : never;

type _Pipe<T extends any[], R extends any[]=[]> = {
 0: Reverse<R>,
 1: _Pipe<Tail<T>, Cons<Tuple2Fn<Head<T>>, R>>
}[T extends [] ? 0 : 1];

type Pipe<T extends any[]>=_Pipe<ShiftZip<T>>;

declare function pipe<T extends any[]>(...f: Pipe<T>): (x: Head<T>) => Last<T>;

Expected behavior:
tsc finish

Actual behavior:
tsc does not finish

Playground Link:

Related Issues:
#24897

[KiaraGrouwstra]

I gotta admit non-terminating compilation is the toughest issue to debug in TypeScript, as it doesn't leave you with a stack trace... type recursion is still pretty much 'here be dragons' territory. :)

To debug, you may wanna first comment bits to see which call is actually triggering the non-terminating recursion, then figure out which recursion termination condition is not going as expected (what's the type it's getting in you expected to terminate execution yet didn't?).

Trying to unit-test with recursive types and random issues like this gets even worse. :)

Edit: すみません、英語が下手だと見落としてしまいました。
TSは確かにこういうエラーがもっともめんどくさいですね。（ｗ）
コードはまだためしてないが、まずタイプを一つ一つコメントしたら、エラッたタイプを見つけるはずです。
見つかったら、回帰の条件をなぜ満たしていないのが見分けるはずです。

[AlCalzone]

Related to, or maybe even a duplicate of #26155?

I've found the recursive Reverse and Concat/Zip definitions to be extremely prone to stalling the language server.

[kgtkr]

tsserverのクラッシュは何度も発生しました
しかしそのようなコードもtscを使えば正常にコンパイルすることが出来ましたし、tsserverを再起動すれば復活します
しかしこのコードはtscでもコンパイル出来ませんし、tsserverを再起動しても復活しません
tscの詳しい内部を知らないので #26155 と関連している問題かは分かりません

Tsserver crash occurred many times
However, such code could be successfully compiled using tsc, restarting tsserver will restore
However, this code can not be compiled with tsc, nor is it restored by restarting tsserver
I do not know the detailed internal of tsc so I do not know if it is related to # 26155

[KiaraGrouwstra]

kgtkr (@kgtkr): Yeah, #26155 is mostly just another bug that occurs with recursive types.

Trying your code at TS Playground (version 3.0.1-insiders.20180726), Head, Tail, Last and Reverse work okay for me.
From Zip I get any as a return type, but when I add Pipe the browser tab hangs for me too...

Maybe the recursion is failing because Zip (and later types) aren't working well?

[RyanCavanaugh]

See comments in #25942 - we don't have any near-term ideas for detecting non-terminating type computations nor good ideas on how to issue useful diagnostics for them.

[RyanCavanaugh]

This quickly errors now.

halting problem: solved