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Construct intersection types for type guards involving type parameters

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This commit is contained in:
Anders Hejlsberg
2017-03-05 14:12:55 -08:00
parent 4c71a7c084
commit 91b658da36
1 changed files with 13 additions and 7 deletions
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20
src/compiler/checker.ts
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@@ -9843,9 +9843,8 @@ namespace ts {
if (flags & TypeFlags.NonPrimitive) {
return strictNullChecks ? TypeFacts.ObjectStrictFacts : TypeFacts.ObjectFacts;
}
if (flags & TypeFlags.TypeParameter) {
const constraint = getConstraintOfTypeParameter(<TypeParameter>type);
return getTypeFacts(constraint || emptyObjectType);
if (flags & TypeFlags.TypeVariable) {
return getTypeFacts(getBaseConstraintOfType(<TypeVariable>type) || emptyObjectType);
}
if (flags & TypeFlags.UnionOrIntersection) {
return getTypeFactsOfTypes((<UnionOrIntersectionType>type).types);
@@ -10632,8 +10631,16 @@ namespace ts {
// is a supertype of that primitive type. For example, type 'any' can be narrowed
// to one of the primitive types.
const targetType = typeofTypesByName.get(literal.text);
if (targetType && isTypeSubtypeOf(targetType, type)) {
return targetType;
if (targetType) {
if (isTypeSubtypeOf(targetType, type)) {
return targetType;
}
if (type.flags & TypeFlags.TypeVariable) {
const constraint = getBaseConstraintOfType(<TypeVariable>type) || anyType;
if (isTypeSubtypeOf(targetType, constraint)) {
return getIntersectionType([type, targetType]);
}
}
}
}
const facts = assumeTrue ?
@@ -10731,10 +10738,9 @@ namespace ts {
// 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.
const targetType = type.flags & TypeFlags.TypeParameter ? getApparentType(type) : type;
return isTypeSubtypeOf(candidate, type) ? candidate :
isTypeAssignableTo(type, candidate) ? type :
isTypeAssignableTo(candidate, targetType) ? candidate :
isTypeAssignableTo(candidate, type) ? candidate :
getIntersectionType([type, candidate]);
}