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Handle type variables in isTypeDerivedFrom

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Anders Hejlsberg 2017-11-19 09:50:33 -08:00
parent 6c4c10c7cf
commit 40579472a2
1 changed files with 2 additions and 0 deletions
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src/compiler/checker.ts
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@ -8868,6 +8868,7 @@ namespace ts {
// An object type S is considered to be derived from an object type T if
// S is a union type and every constituent of S is derived from T,
// T is a union type and S is derived from at least one constituent of T, or
// S is a type variable with a base constraint that is derived from T,
// T is one of the global types Object and Function and S is a subtype of T, or
// T occurs directly or indirectly in an 'extends' clause of S.
// Note that this check ignores type parameters and only considers the
@ -8875,6 +8876,7 @@ namespace ts {
function isTypeDerivedFrom(source: Type, target: Type): boolean {
return source.flags & TypeFlags.Union ? every((<UnionType>source).types, t => isTypeDerivedFrom(t, target)) :
target.flags & TypeFlags.Union ? some((<UnionType>target).types, t => isTypeDerivedFrom(source, t)) :
source.flags & TypeFlags.TypeVariable ? isTypeDerivedFrom(getBaseConstraintOfType(source) || emptyObjectType, target) :
target === globalObjectType || target === globalFunctionType ? isTypeSubtypeOf(source, target) :
hasBaseType(source, getTargetType(target));
}