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Fixed distributive conditional types with never intersections (#57345)

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This commit is contained in:
Mateusz Burzyński
2024-02-09 12:25:02 -08:00
committed by GitHub
parent c5db0ac0ef
commit e2bf8b437d
4 changed files with 70 additions and 2 deletions
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src/compiler/checker.ts
+2 -2
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@@ -19877,12 +19877,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
if (!result) {
const newMapper = createTypeMapper(root.outerTypeParameters, typeArguments);
const checkType = root.checkType;
const distributionType = root.isDistributive ? getMappedType(checkType, newMapper) : undefined;
const distributionType = root.isDistributive ? getReducedType(getMappedType(checkType, newMapper)) : undefined;
// Distributive conditional types are distributed over union types. For example, when the
// distributive conditional type T extends U ? X : Y is instantiated with A | B for T, the
// result is (A extends U ? X : Y) | (B extends U ? X : Y).
result = distributionType && checkType !== distributionType && distributionType.flags & (TypeFlags.Union | TypeFlags.Never) ?
mapTypeWithAlias(getReducedType(distributionType), t => getConditionalType(root, prependTypeMapping(checkType, t, newMapper), forConstraint), aliasSymbol, aliasTypeArguments) :
mapTypeWithAlias(distributionType, t => getConditionalType(root, prependTypeMapping(checkType, t, newMapper), forConstraint), aliasSymbol, aliasTypeArguments) :
getConditionalType(root, newMapper, forConstraint, aliasSymbol, aliasTypeArguments);
root.instantiations!.set(id, result);
}