Check for type parameters on the original type when asking for the ty…

…pe argument constraint.
microsoft · Nov 1, 2021 · 3c0d51b · 3c0d51b
1 parent e77514a
commit 3c0d51b
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -34729,7 +34729,8 @@ namespace ts {
         function getTypeArgumentConstraint(node: TypeNode): Type | undefined {
             const typeReferenceNode = tryCast(node.parent, isTypeReferenceType);
             if (!typeReferenceNode) return undefined;
-            const typeParameters = getTypeParametersForTypeReference(typeReferenceNode)!; // TODO: GH#18217
+            const typeParameters = getTypeParametersForTypeReference(typeReferenceNode);
+            if (!typeParameters) return undefined;
             const constraint = getConstraintOfTypeParameter(typeParameters[typeReferenceNode.typeArguments!.indexOf(node)]);
             return constraint && instantiateType(constraint, createTypeMapper(typeParameters, getEffectiveTypeArguments(typeReferenceNode, typeParameters)));
         }