Handle type variables in isTypeDerivedFrom
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@ -8868,6 +8868,7 @@ namespace ts {
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// An object type S is considered to be derived from an object type T if
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// S is a union type and every constituent of S is derived from T,
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// T is a union type and S is derived from at least one constituent of T, or
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// S is a type variable with a base constraint that is derived from T,
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// T is one of the global types Object and Function and S is a subtype of T, or
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// T occurs directly or indirectly in an 'extends' clause of S.
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// Note that this check ignores type parameters and only considers the
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@ -8875,6 +8876,7 @@ namespace ts {
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function isTypeDerivedFrom(source: Type, target: Type): boolean {
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return source.flags & TypeFlags.Union ? every((<UnionType>source).types, t => isTypeDerivedFrom(t, target)) :
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target.flags & TypeFlags.Union ? some((<UnionType>target).types, t => isTypeDerivedFrom(source, t)) :
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source.flags & TypeFlags.TypeVariable ? isTypeDerivedFrom(getBaseConstraintOfType(source) || emptyObjectType, target) :
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target === globalObjectType || target === globalFunctionType ? isTypeSubtypeOf(source, target) :
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hasBaseType(source, getTargetType(target));
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}
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