check if instantiable type constraint allows spread

Author: collin5

src/compiler/checker.ts

@@ -19222,6 +19222,12 @@ namespace ts {
         }
 
         function isValidSpreadType(type: Type): boolean {
+            if (type.flags & TypeFlags.Instantiable) {
+                const constraint = getBaseConstraintOfType(type);
+                if (constraint !== undefined) {
+                    return isValidSpreadType(constraint);
+                }
+            }
             return !!(type.flags & (TypeFlags.AnyOrUnknown | TypeFlags.NonPrimitive | TypeFlags.Object | TypeFlags.InstantiableNonPrimitive) ||
                 getFalsyFlags(type) & TypeFlags.DefinitelyFalsy && isValidSpreadType(removeDefinitelyFalsyTypes(type)) ||
                 type.flags & TypeFlags.UnionOrIntersection && every((<UnionOrIntersectionType>type).types, isValidSpreadType));