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Favor asserted type in type predicate narrowing #50044

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Merged
merged 2 commits into from
Jul 27, 2022
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Favor asserted type in type predicate narrowing #50044

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1e96c57
Favor asserted type in type predicate narrowing
ahejlsberg Jul 25, 2022
a9484d3
Accept new baselines
ahejlsberg Jul 25, 2022
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8 changes: 6 additions & 2 deletions src/compiler/checker.ts
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Expand Up @@ -25428,8 +25428,12 @@ namespace ts {
const discriminant = keyPropertyName && getTypeOfPropertyOfType(c, keyPropertyName);
const matching = discriminant && getConstituentTypeForKeyType(type as UnionType, discriminant);
// For each constituent t in the current type, if t and and c are directly related, pick the most
// specific of the two.
const directlyRelated = mapType(matching || type, t => isRelated(t, c) ? t : isRelated(c, t) ? c : neverType);
// specific of the two. When t and c are related in both directions, we prefer c for type predicates
// because that is the asserted type, but t for `instanceof` because generics aren't reflected in
// prototype object types.
const directlyRelated = mapType(matching || type, checkDerived ?
t => isTypeDerivedFrom(t, c) ? t : isTypeDerivedFrom(c, t) ? c : neverType :
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@DanielRosenwasser DanielRosenwasser Jul 26, 2022 •
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Why do you need the new isTypeDerivedFrom checks too?

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The isTypeDerivedFrom check isn't new. It's just that I'm calling it directly instead of indirectly through the isRelated local. Once we know checkDerived is true, we also know that isRelated references isTypeDerivedFrom, so might as well call it directly.

t => isTypeSubtypeOf(c, t) ? c : isTypeSubtypeOf(t, c) ? t : neverType);
// If no constituents are directly related, create intersections for any generic constituents that
// are related by constraint.
return directlyRelated.flags & TypeFlags.Never ?
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8 changes: 4 additions & 4 deletions tests/baselines/reference/controlFlowBinaryOrExpression.symbols
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Expand Up @@ -64,19 +64,19 @@ if (isNodeList(sourceObj)) {
>sourceObj : Symbol(sourceObj, Decl(controlFlowBinaryOrExpression.ts, 23, 3))

sourceObj.length;
>sourceObj.length : Symbol(length, Decl(controlFlowBinaryOrExpression.ts, 10, 27), Decl(controlFlowBinaryOrExpression.ts, 14, 33))
>sourceObj.length : Symbol(NodeList.length, Decl(controlFlowBinaryOrExpression.ts, 10, 27))
>sourceObj : Symbol(sourceObj, Decl(controlFlowBinaryOrExpression.ts, 23, 3))
>length : Symbol(length, Decl(controlFlowBinaryOrExpression.ts, 10, 27), Decl(controlFlowBinaryOrExpression.ts, 14, 33))
>length : Symbol(NodeList.length, Decl(controlFlowBinaryOrExpression.ts, 10, 27))
}

if (isHTMLCollection(sourceObj)) {
>isHTMLCollection : Symbol(isHTMLCollection, Decl(controlFlowBinaryOrExpression.ts, 18, 67))
>sourceObj : Symbol(sourceObj, Decl(controlFlowBinaryOrExpression.ts, 23, 3))

sourceObj.length;
>sourceObj.length : Symbol(length, Decl(controlFlowBinaryOrExpression.ts, 10, 27), Decl(controlFlowBinaryOrExpression.ts, 14, 33))
>sourceObj.length : Symbol(HTMLCollection.length, Decl(controlFlowBinaryOrExpression.ts, 14, 33))
>sourceObj : Symbol(sourceObj, Decl(controlFlowBinaryOrExpression.ts, 23, 3))
>length : Symbol(length, Decl(controlFlowBinaryOrExpression.ts, 10, 27), Decl(controlFlowBinaryOrExpression.ts, 14, 33))
>length : Symbol(HTMLCollection.length, Decl(controlFlowBinaryOrExpression.ts, 14, 33))
}

if (isNodeList(sourceObj) || isHTMLCollection(sourceObj)) {
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8 changes: 4 additions & 4 deletions tests/baselines/reference/controlFlowBinaryOrExpression.types
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Expand Up @@ -69,26 +69,26 @@ if (isNodeList(sourceObj)) {

sourceObj.length;
>sourceObj.length : number
>sourceObj : NodeList | HTMLCollection
>sourceObj : NodeList
>length : number
}

if (isHTMLCollection(sourceObj)) {
>isHTMLCollection(sourceObj) : boolean
>isHTMLCollection : (sourceObj: any) => sourceObj is HTMLCollection
>sourceObj : EventTargetLike
>sourceObj : NodeList | { a: string; }

sourceObj.length;
>sourceObj.length : number
>sourceObj : NodeList | HTMLCollection
>sourceObj : HTMLCollection
>length : number
}

if (isNodeList(sourceObj) || isHTMLCollection(sourceObj)) {
>isNodeList(sourceObj) || isHTMLCollection(sourceObj) : boolean
>isNodeList(sourceObj) : boolean
>isNodeList : (sourceObj: any) => sourceObj is NodeList
>sourceObj : EventTargetLike
>sourceObj : HTMLCollection | { a: string; }
>isHTMLCollection(sourceObj) : boolean
>isHTMLCollection : (sourceObj: any) => sourceObj is HTMLCollection
>sourceObj : { a: string; }
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4 changes: 2 additions & 2 deletions tests/baselines/reference/instanceofWithStructurallyIdenticalTypes.symbols
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Expand Up @@ -95,9 +95,9 @@ function foo2(x: C1 | C2 | C3): string {
>x : Symbol(x, Decl(instanceofWithStructurallyIdenticalTypes.ts, 23, 14))

return x.item;
>x.item : Symbol(item, Decl(instanceofWithStructurallyIdenticalTypes.ts, 2, 10), Decl(instanceofWithStructurallyIdenticalTypes.ts, 4, 10))
>x.item : Symbol(C1.item, Decl(instanceofWithStructurallyIdenticalTypes.ts, 2, 10))
>x : Symbol(x, Decl(instanceofWithStructurallyIdenticalTypes.ts, 23, 14))
>item : Symbol(item, Decl(instanceofWithStructurallyIdenticalTypes.ts, 2, 10), Decl(instanceofWithStructurallyIdenticalTypes.ts, 4, 10))
>item : Symbol(C1.item, Decl(instanceofWithStructurallyIdenticalTypes.ts, 2, 10))
}
else if (isC2(x)) {
>isC2 : Symbol(isC2, Decl(instanceofWithStructurallyIdenticalTypes.ts, 19, 66))
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2 changes: 1 addition & 1 deletion tests/baselines/reference/instanceofWithStructurallyIdenticalTypes.types
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Expand Up @@ -85,7 +85,7 @@ function foo2(x: C1 | C2 | C3): string {

return x.item;
>x.item : string
>x : C1 | C3
>x : C1
>item : string
}
else if (isC2(x)) {
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4 changes: 2 additions & 2 deletions tests/baselines/reference/typePredicateStructuralMatch.symbols
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Expand Up @@ -51,9 +51,9 @@ function getResults1(value: Results | { data: Results }): Results {
return isResponseInData(value) ? value.data : value;
>isResponseInData : Symbol(isResponseInData, Decl(typePredicateStructuralMatch.ts, 9, 24))
>value : Symbol(value, Decl(typePredicateStructuralMatch.ts, 15, 21))
>value.data : Symbol(data, Decl(typePredicateStructuralMatch.ts, 15, 39))
>value.data : Symbol(data, Decl(typePredicateStructuralMatch.ts, 11, 63))
>value : Symbol(value, Decl(typePredicateStructuralMatch.ts, 15, 21))
>data : Symbol(data, Decl(typePredicateStructuralMatch.ts, 15, 39))
>data : Symbol(data, Decl(typePredicateStructuralMatch.ts, 11, 63))
>value : Symbol(value, Decl(typePredicateStructuralMatch.ts, 15, 21))
}

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2 changes: 1 addition & 1 deletion tests/baselines/reference/unionWithIndexSignature.types
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Expand Up @@ -55,7 +55,7 @@ export function flatten<T extends number|TypedArray>(arr: T) {

arr[1];
>arr[1] : number
>arr : TypedArray
>arr : Int32Array | Uint8Array
>1 : 1
}
}
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