After updating to 3.x.x getting TS2536

TypeScript Version: typescript@3.3.0-dev.20181122

Search Terms:
TS2536 Record Map vuex

Code

interface ITest {
  expectedStr: string;
  expectedN: number;
}

interface MapAccessor<Getters> {
  <T = Getters, Map extends Record<string, keyof T> = Record<string, keyof T>>(
    map: Map
  ): { [K in keyof Map]: (() => T[Map[K]]) };
}

interface TestAccess {
  str: "expectedStr";
}

const t: MapAccessor<ITest> = {} as any;

const str = t({
  str: "expectedStr"
}).str;

Expected behavior:
No compile issue, is working using typescript@3.0.1, checked the breaking changes and found nothing in regards to this.

Intellisense still works as expected giving error if you change expectedStr to an invalid value.

Actual behavior:
Not giving error: index.ts:9:33 - error TS2536: Type 'Map[K]' cannot be used to index type 'T'.

Playground Link:
playground

This might be affected by this: #27490 (and thus working as intended).

Map[K] is no longer pulling in the constraint keyof T because both Map and K are generic.

I'd wait on a final say from someone on the team though,

What I find odd is the intellisense/editor picking up the correct value.

Is there a way to have the same behavior without the error?

Is your editor using an older version of tsserver?

I'm using VSCode and even the typescript playground it works (even with the error it resolves the correct type).

playground

EDIT:

I think @jack-williams is right; but I'm unsure if we wanted this specific kind of pattern to break

This is working as intended. A simplified example:

function f1<T, U extends Record<string, keyof T>, K extends keyof U>(obj: T, map: U, key: K) {
    return obj[map[key]];  // Error
}

Here, U is constrained to an object type where properties with string names are constrained to keyof T. However, it is possible for an instantiation to supply a type argument for U that has properties with symbol names which aren't constrained in any way. Therefore U[K] isn't known to be constrained to keyof T.

Changing the constraint of U to an object type where all properties are constrained to keyof T does indeed work:

function f2<T, U extends Record<keyof U, keyof T>, K extends keyof U>(obj: T, map: U, key: K) {
    return obj[map[key]];  // Ok
}

Yep, so it seems like I was completely wrong on this one. The mistake I made was that the PR I linked to only concerned the case when relating to an indexed access type; this example is about relating from an indexed access type. Subtle, but wrong. Sorry!

cc @DanielRosenwasser to double-check that we're documenting this break in the 3.2 (? I think that's the first) release.

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

Sorry to comment on a closed issue, is this suppose to happen:

interface MyGetter {
    vstring : string,
    vnumber: number,

    vhidden: boolean;
}
declare interface TestGeneric<Getters> {
    <Map extends Record<string, keyof Getters>>(map: Map) : { [K in keyof Map]: Getters[Map[K]]}; 
}

declare interface TestSpecific {
    <Map extends Record<string, keyof MyGetter>>(map: Map): { [K in keyof Map]: MyGetter[Map[K]]}
}

declare const genericInterface: TestGeneric<MyGetter>;
declare const speficInterface: TestSpecific;

const generic = genericInterface({
    testString: 'vstring',
    testNumber: 'vnumber'
});
const specific = speficInterface({
    testString: 'vstring',
    testNumber: 'vnumber'
}); 


generic.testNumber; //number
specific.testNumber; // number

generic.testString; // string
specific.testString; //string

TestGeneric is getting a compile error but TestSpecific doesn't, shouldn't the type be correct?

playground

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After updating to 3.x.x getting TS2536 #28647

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After updating to 3.x.x getting TS2536 #28647

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jack-williams commented on Nov 22, 2018

pikax commented on Nov 23, 2018

jack-williams commented on Nov 23, 2018

pikax commented on Nov 23, 2018

weswigham commented on Nov 26, 2018

ahejlsberg commented on Nov 26, 2018

jack-williams commented on Nov 26, 2018

weswigham commented on Nov 26, 2018

typescript-bot commented on Dec 13, 2018

pikax commented on Feb 14, 2019

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