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Remove assignability cases in getNarrowedType + an isArray improvement for readonly arrays (#39258)

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* Explore using a different isArray declaration

* Add tests and the new isArray definition

* Baseline updates

* Upda the isArray type
This commit is contained in:
Orta Therox
2020-09-08 14:43:48 -04:00
committed by GitHub
parent 1d2278be05
commit fa89ce6158
23 changed files with 700 additions and 63 deletions
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14
src/compiler/checker.ts
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@@ -21984,15 +21984,11 @@ namespace ts {
return assignableType;
}
}
// If the candidate type is a subtype of the target type, narrow to the candidate type.
// Otherwise, if the target type is assignable to the candidate type, keep the target type.
// Otherwise, if the candidate type is assignable to the target type, narrow to the candidate
// type. Otherwise, the types are completely unrelated, so narrow to an intersection of the
// two types.
return isTypeSubtypeOf(candidate, type) ? candidate :
isTypeAssignableTo(type, candidate) ? type :
isTypeAssignableTo(candidate, type) ? candidate :
getIntersectionType([type, candidate]);
// If the candidate type is a subtype of the target type, narrow to the candidate type,
// if the target type is a subtype of the candidate type, narrow to the target type,
// otherwise, narrow to an intersection of the two types.
return isTypeSubtypeOf(candidate, type) ? candidate : isTypeSubtypeOf(type, candidate) ? type : getIntersectionType([type, candidate]);
}
function narrowTypeByCallExpression(type: Type, callExpression: CallExpression, assumeTrue: boolean): Type {

2
src/lib/es5.d.ts vendored
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@@ -1376,7 +1376,7 @@ interface ArrayConstructor {
(arrayLength?: number): any[];
<T>(arrayLength: number): T[];
<T>(...items: T[]): T[];
isArray(arg: any): arg is any[];
isArray<T>(arg: T | {}): arg is T extends readonly any[] ? (unknown extends T ? never : readonly any[]) : any[];
readonly prototype: any[];
}