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Reuse existing type instantiations

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This commit is contained in:
Anders Hejlsberg 2019-05-11 11:15:37 -07:00
parent 33c7e7fd2c
commit bb9c5c96c8
1 changed files with 2 additions and 2 deletions
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4
src/compiler/checker.ts
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@ -10379,7 +10379,7 @@ namespace ts {
// Simplifications for types of the form `T extends U ? T : never` and `T extends U ? never : T`.
if (root.falseType.flags & TypeFlags.Never && getActualTypeVariable(root.trueType) === getActualTypeVariable(root.checkType)) {
if (checkType.flags & TypeFlags.Any || isTypeAssignableTo(getRestrictiveInstantiation(checkType), getRestrictiveInstantiation(extendsType))) { // Always true
return instantiateType(root.trueType, mapper);
return checkType;
}
else if (isIntersectionEmpty(checkType, extendsType)) { // Always false
return neverType;
@ -10390,7 +10390,7 @@ namespace ts {
return neverType;
}
else if (checkType.flags & TypeFlags.Any || isIntersectionEmpty(checkType, extendsType)) { // Always false
return instantiateType(root.falseType, mapper);
return checkType;
}
}
const checkTypeInstantiable = maybeTypeOfKind(checkType, TypeFlags.Instantiable | TypeFlags.GenericMappedType);