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Improve detection of cases where subtype reduction is unnecessary (#53435)

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This commit is contained in:
Anders Hejlsberg
2023-03-23 07:09:12 -07:00
committed by GitHub
parent 37bafa539c
commit 511921e1e2
4 changed files with 128 additions and 4 deletions
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8
src/compiler/checker.ts
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@@ -25891,7 +25891,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}
function isTypeSubsetOf(source: Type, target: Type) {
return source === target || target.flags & TypeFlags.Union && isTypeSubsetOfUnion(source, target as UnionType);
return !!(source === target || source.flags & TypeFlags.Never || target.flags & TypeFlags.Union && isTypeSubsetOfUnion(source, target as UnionType));
}
function isTypeSubsetOfUnion(source: Type, target: UnionType) {
@@ -26715,7 +26715,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
// If an antecedent type is not a subset of the declared type, we need to perform
// subtype reduction. This happens when a "foreign" type is injected into the control
// flow using the instanceof operator or a user defined type predicate.
if (!isTypeSubsetOf(type, declaredType)) {
if (!isTypeSubsetOf(type, initialType)) {
subtypeReduction = true;
}
if (isIncomplete(flowType)) {
@@ -26733,7 +26733,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
return type;
}
antecedentTypes.push(type);
if (!isTypeSubsetOf(type, declaredType)) {
if (!isTypeSubsetOf(type, initialType)) {
subtypeReduction = true;
}
if (isIncomplete(flowType)) {
@@ -26808,7 +26808,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
// If an antecedent type is not a subset of the declared type, we need to perform
// subtype reduction. This happens when a "foreign" type is injected into the control
// flow using the instanceof operator or a user defined type predicate.
if (!isTypeSubsetOf(type, declaredType)) {
if (!isTypeSubsetOf(type, initialType)) {
subtypeReduction = true;
}
// If the type at a particular antecedent path is the declared type there is no