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Allow assignability of non-empty object to generic mapped type #32071

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Jul 1, 2019
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Allow assignability of non-empty object to generic mapped type #32071

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7bbd299
Look at properties of constraint-instantiated optional mapped types w…
andrewbranch Jun 24, 2019
79c6048
Use intersectTypes instead of filterType
andrewbranch Jun 26, 2019
27b8c45
Update baselines
andrewbranch Jul 1, 2019
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8 changes: 4 additions & 4 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -13200,14 +13200,14 @@ namespace ts {
if (!isGenericMappedType(source)) {
const targetConstraint = getConstraintTypeFromMappedType(target);
const sourceKeys = getIndexType(source, /*stringsOnly*/ undefined, /*noIndexSignatures*/ true);
const hasOptionalUnionKeys = modifiers & MappedTypeModifiers.IncludeOptional && targetConstraint.flags & TypeFlags.Union;
const filteredByApplicability = hasOptionalUnionKeys ? filterType(targetConstraint, t => !!isRelatedTo(t, sourceKeys)) : undefined;
const includeOptional = modifiers & MappedTypeModifiers.IncludeOptional;
const filteredByApplicability = includeOptional ? intersectTypes(targetConstraint, sourceKeys) : undefined;
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My expectation was that when a mapped type target was instantiated with some T with a constraint like { x: number }, either getConstraintTypeFromMappedType(target) or getIndexType(target) would essentially give me keyof { x: number }. But instead, they both give me a fairly unhelpful index type for a generic object.

So then I thought, “ah, maybe if I use the apparent type of the mapped type,” but in the test case I added, getApparentType(target) === target.

My true intent was just to get a plain object type for that instantiation of that generic mapped type, at which point I think I could just call isRelatedTo(source, plainObjectType).

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If the constraint is keyof U | "a" | "b", getLiteralTypeFromProperties is going to ignore the U-ness of the keyof U part, while the targetConstraint will keep it. We'd like to keep as a keyof (T extends Entity) is different from a keyof (U extends Entity) and needs to be recognized as such. Rather than the filtering using filterType to calculate filteredByApplicability as we're doing now, it's actually probably best to use intersectTypes(targetConstraint, sourceKeys) since the result is the overlapping keys (be they generic or not). Making the indexed access below with that intersection should then work dandily.

In fact, it seems like this is all the changes needed to fix the issue (from master):

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 64bf09d8b3..4476214e71 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13200,8 +13200,8 @@ namespace ts {
                         if (!isGenericMappedType(source)) {
                             const targetConstraint = getConstraintTypeFromMappedType(target);
                             const sourceKeys = getIndexType(source, /*stringsOnly*/ undefined, /*noIndexSignatures*/ true);
-                            const hasOptionalUnionKeys = modifiers & MappedTypeModifiers.IncludeOptional && targetConstraint.flags & TypeFlags.Union;
-                            const filteredByApplicability = hasOptionalUnionKeys ? filterType(targetConstraint, t => !!isRelatedTo(t, sourceKeys)) : undefined;
+                            const hasOptionalUnionKeys = modifiers & MappedTypeModifiers.IncludeOptional;
+                            const filteredByApplicability = hasOptionalUnionKeys ? intersectTypes(targetConstraint, sourceKeys) : undefined;
                             // A source type T is related to a target type { [P in Q]: X } if Q is related to keyof T and T[Q] is related to X.
                             // A source type T is related to a target type { [P in Q]?: X } if some constituent Q' of Q is related to keyof T and T[Q'] is related to X.
                             if (hasOptionalUnionKeys

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Oh, fantastic, that’s so much better 🙌

// A source type T is related to a target type { [P in Q]: X } if Q is related to keyof T and T[Q] is related to X.
// A source type T is related to a target type { [P in Q]?: X } if some constituent Q' of Q is related to keyof T and T[Q'] is related to X.
if (hasOptionalUnionKeys
if (includeOptional
? !(filteredByApplicability!.flags & TypeFlags.Never)
: isRelatedTo(targetConstraint, sourceKeys)) {
const indexingType = hasOptionalUnionKeys ? filteredByApplicability! : getTypeParameterFromMappedType(target);
const indexingType = filteredByApplicability || getTypeParameterFromMappedType(target);
const indexedAccessType = getIndexedAccessType(source, indexingType);
const templateType = getTemplateTypeFromMappedType(target);
if (result = isRelatedTo(indexedAccessType, templateType, reportErrors)) {
Expand Down
156 changes: 98 additions & 58 deletions ...rcularlyConstrainedMappedTypeContainingConditionalNoInfiniteInstantiationDepth.errors.txt
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6 changes: 6 additions & 0 deletions tests/baselines/reference/mappedTypeRelationships.errors.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -386,4 +386,10 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(168,5): error TS
function f82<T, K1 extends keyof T, K2 extends keyof T[K1]>(t: T, k1: K1, k2: K2): Partial<T[K1][K2]> {
return t[k1][k2];
}

// #31070
type Numeric<T> = { [K in keyof T]?: number };
function f90<T extends { x: number }>() {
const n: Numeric<T> = { x: 1 };
}

15 changes: 15 additions & 0 deletions tests/baselines/reference/mappedTypeRelationships.js
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Expand Up @@ -180,6 +180,12 @@ function f81<T, K extends keyof T>(t: T, k: K): Partial<T[K]> {
function f82<T, K1 extends keyof T, K2 extends keyof T[K1]>(t: T, k1: K1, k2: K2): Partial<T[K1][K2]> {
return t[k1][k2];
}

// #31070
type Numeric<T> = { [K in keyof T]?: number };
function f90<T extends { x: number }>() {
const n: Numeric<T> = { x: 1 };
}


//// [mappedTypeRelationships.js]
Expand Down Expand Up @@ -310,6 +316,9 @@ function f81(t, k) {
function f82(t, k1, k2) {
return t[k1][k2];
}
function f90() {
var n = { x: 1 };
}


//// [mappedTypeRelationships.d.ts]
Expand Down Expand Up @@ -393,3 +402,9 @@ declare function f76<T, U extends T, K extends keyof T>(x: {
declare function f80<T>(t: T): Partial<T>;
declare function f81<T, K extends keyof T>(t: T, k: K): Partial<T[K]>;
declare function f82<T, K1 extends keyof T, K2 extends keyof T[K1]>(t: T, k1: K1, k2: K2): Partial<T[K1][K2]>;
declare type Numeric<T> = {
[K in keyof T]?: number;
};
declare function f90<T extends {
x: number;
}>(): void;
19 changes: 19 additions & 0 deletions tests/baselines/reference/mappedTypeRelationships.symbols
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Expand Up @@ -805,3 +805,22 @@ function f82<T, K1 extends keyof T, K2 extends keyof T[K1]>(t: T, k1: K1, k2: K2
>k2 : Symbol(k2, Decl(mappedTypeRelationships.ts, 178, 73))
}

// #31070
type Numeric<T> = { [K in keyof T]?: number };
>Numeric : Symbol(Numeric, Decl(mappedTypeRelationships.ts, 180, 1))
>T : Symbol(T, Decl(mappedTypeRelationships.ts, 183, 13))
>K : Symbol(K, Decl(mappedTypeRelationships.ts, 183, 21))
>T : Symbol(T, Decl(mappedTypeRelationships.ts, 183, 13))

function f90<T extends { x: number }>() {
>f90 : Symbol(f90, Decl(mappedTypeRelationships.ts, 183, 46))
>T : Symbol(T, Decl(mappedTypeRelationships.ts, 184, 13))
>x : Symbol(x, Decl(mappedTypeRelationships.ts, 184, 24))

const n: Numeric<T> = { x: 1 };
>n : Symbol(n, Decl(mappedTypeRelationships.ts, 185, 9))
>Numeric : Symbol(Numeric, Decl(mappedTypeRelationships.ts, 180, 1))
>T : Symbol(T, Decl(mappedTypeRelationships.ts, 184, 13))
>x : Symbol(x, Decl(mappedTypeRelationships.ts, 185, 27))
}

15 changes: 15 additions & 0 deletions tests/baselines/reference/mappedTypeRelationships.types
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Expand Up @@ -653,3 +653,18 @@ function f82<T, K1 extends keyof T, K2 extends keyof T[K1]>(t: T, k1: K1, k2: K2
>k2 : K2
}

// #31070
type Numeric<T> = { [K in keyof T]?: number };
>Numeric : Numeric<T>

function f90<T extends { x: number }>() {
>f90 : <T extends { x: number; }>() => void
>x : number

const n: Numeric<T> = { x: 1 };
>n : Numeric<T>
>{ x: 1 } : { x: number; }
>x : number
>1 : 1
}

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