Add transformation to indexing intersection of homomorphic mapepd type and generic parameter #25490
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…e and generic parameter
| newMappedType.typeParameter = (t as MappedType).typeParameter; | ||
| newMappedType.constraintType = (t as MappedType).constraintType; | ||
| const newSet = (<IntersectionType>objectType).types.slice(); | ||
| newSet.splice(matchIndex!, 1); // Remove the generic |
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orderedRemoveItemAt (or unorderedRemoveItemAt if it doesn't matter)
| newMappedType.constraintType = (t as MappedType).constraintType; | ||
| const newSet = (<IntersectionType>objectType).types.slice(); | ||
| newSet.splice(matchIndex!, 1); // Remove the generic | ||
| newSet.splice(newSet.indexOf(t), 1, newMappedType); // Remove the original mapped type |
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Why not directly overwrite the original location?
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... fair point. I was in a splicy mood, I suppose.
| // If we don't do such a transformation now, due to how we reason over intersections, we will never come to the | ||
| // realization that the member we're trying to pluck out is influenced by both `T[P]` _and_ the mapped type template | ||
| const isInSet = isMappedTypeOverKeyofGenericInSet((<IntersectionType>objectType).types); | ||
| if (some((<IntersectionType>objectType).types, isInSet)) { |
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Could you turn this into a findIndex and then avoid the inner loop?
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Superseded by #26281, which is much more elegant, IMO. |
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In
getSimplifiedType, adds a branch which transforms(T & {[P in keyof T]: Foo})[K](which we can't reason about, thanks to how we combine the intersection before looking for members on its apparent type) into{[P in keyof T]: T[P] & Foo}[K](which we can reason about).Specifically, in the first case, when calculating its constraint, we see that it's an indexed access, attempt to simplify it (and it doesn't), then we get the base constraints of
T & {[P in keyof T]: Foo}andK, and produce a new indexed access - that becomes({} & {})[string | number | symbol], which then becomes theerrortype.Now, when we attempt to simplify it, we apply the above mapping, and the index type
{[P in keyof T]: T[P] & Foo}[K]in the provided sample simplifies toT[K] & Foo(sinceKiskeyof T) whose constraint is simplyFoo.Fixes #25181