4.9 regression on conditional type

[testerez]

Bug Report

🔎 Search Terms

4.9 Type 'number' does not satisfy the constraint

🕗 Version & Regression Information

This changed between versions 4.8 and 4.9.3

⏯ Playground Link

tsplay.dev/NdrGyW

💻 Code

type Decrement<N extends number> = [-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10][N]

type PathImpl<T, K extends keyof T, Depth extends number> = Depth extends 0
  ? ''
  : K extends string | number
  ? T[K] extends Record<string, any>
    ? T[K] extends ArrayLike<any>
      ? K | `${K}.${PathImpl<T[K], number, Decrement<Depth>>}`
      : K | `${K}.${PathImpl<T[K], keyof T[K], Decrement<Depth>>}`
    : K
  : never

export type ObjectPath<T> = PathImpl<T, keyof T, 10> | keyof T

🙁 Actual behavior

Type 'number' does not satisfy the constraint 'keyof T[K]'.

🙂 Expected behavior

Since T[K] extends ArrayLike<any> then I should be able to index by number. This was working on 4.8

[Tobias-Scholz]

Here is a slightly smaller example to reproduce the issue.

Playground

type PathImpl<T, K extends keyof T> = 
  K extends string | number
  ? T[K] extends Record<string, any>
    ? T[K] extends ArrayLike<any>
      ? PathImpl<T[K], number>
      : never
    : never
  : never

All three conditionals are needed to reproduce the error.

There is no error if you remove the first conditional.

type PathImpl<T, K extends keyof T> = 
  T[K] extends Record<string, any>
    ? T[K] extends ArrayLike<any>
      ? PathImpl<T[K], number>
      : never
    : never

Which seems counterintuitive to me.

[cjbarth]

I think we might have a similar issue, but it is related to keyof typeof this.privateMember. See node-saml/node-saml#218

[typescript-bot]

The change between release-4.8 and main occurred at 6e8337e.

[JGJP]

Seeing a similar issue in @storybook/components popperjs typing, it fails with this message:

Type 'Options' does not satisfy the constraint 'Obj'

where the code looks like this:

export declare type Modifier<Name, Options> = {
    name: Name;
    enabled: boolean;
    phase: ModifierPhases;
    requires?: Array<string>;
    requiresIfExists?: Array<string>;
    fn: (arg0: ModifierArguments<Options>) => State | void; // <-- fails here
    effect?: (arg0: ModifierArguments<Options>) => (() => void) | void; // <-- and here
    options?: Partial<Options>;
    data?: Obj;
};

export declare type ModifierArguments<Options extends Obj> = {
    state: State;
    instance: Instance;
    options: Partial<Options>;
    name: string;
};

export declare type Obj = {
    [key: string]: any;
};

So it looks like it's failing to assign an untyped generic arg to { [key: string]: any }. Is this expected?

[RyanCavanaugh]

@JGJP that looks like a correct error to me (kinda hard to say since the example is self-contained). Options is unconstrained; if you believe that an unconstrained type parameter should be allowable to pass to a type parameter constrained to Obj, why did you write the extends Obj constraint in the first place?

[JGJP]

@RyanCavanaugh this is not my code, it's from popperjs typings, used by @storybook/components. It's only broken after upgrading TS, so I assume it was passing type checks before (4.6)

[ahejlsberg]

This issue no longer reproduces. Looks like it was fixed in TS 5.0.