Unexpected "does not satisfy the constraint"

[jamesknelson]

TypeScript Version: 2.2.1

Code

type Group = {
    [key: string]: string;
}

class Foo<G extends Group> {
    attributes: G;
}

declare function createResource<G extends Group>(x: G): Foo<{ [K in keyof G]: string }>;

Expected behavior:

This should compile, I think. { [K in keyof G]: string } does satisfy { [key: string]: string }.

Actual behavior:

The compiler outputs the following:

type-error-demo.ts(9,61): error TS2344: Type '{ [K in keyof G]: string; }' does not satisfy the constraint 'Group'.

---

Use case:

This is a larger example which is closer to the original use case. The idea is to add "keys" to the passed in object's values based on the passed in object's keys.

type AttributeOptions<P> = {
    default: P;
}
type AttributeOptionsSet = {
    [key: string]: AttributeOptions<any>;
}

type Attribute<P> = {
    key: string;
    default: P;
}
type AttributeSet = {
    [key: string]: Attribute<any>;
}

class Resource<As extends AttributeSet> {
    attributes: As;
}

declare function createResource<AOs extends AttributeOptionsSet>(x: AOs): Resource<{ [Key in keyof AOs]: Attribute<AOs[Key]["default"]> }>;

A hacky way to make this compile involves adding a generic to AttributeSet that contains its keys, and letting typescript infer them:

type AttributeOptions<P> = {
    default: P;
}
type AttributeOptionsSet = {
    [key: string]: AttributeOptions<any>;
}

type Attribute<P, Key extends string> = {
    key: Key;
    default: P;
}
type AttributeSet<Keys extends string> = {
    [Key in Keys]: Attribute<any, Key>;
}

class Resource<As extends AttributeSet<keyof As>> {
    attributes: As;
}

// This actually compiles
declare function createResource<AOs extends AttributeOptionsSet>(x: AOs): Resource<{ [Key in keyof AOs]: Attribute<AOs[Key]["default"], Key> }>;

The problem with this is that it causes tsc to fail further through the application code -- see my comment in #14723

[RyanCavanaugh]

Same as #14548