[weld-dev] Odd type assignability test

[Matej Novotny]

----- Original Message -----
> From: "Laird Nelson" <ljnelson at gmail.com>
> To: "weld-dev" <weld-dev at lists.jboss.org>
> Sent: Monday, April 27, 2020 5:51:54 PM
> Subject: Re: [weld-dev] Odd type assignability test
> 
> 
> On Mon, Apr 27, 2020 at 5:38 AM Martin Kouba < mkouba at redhat.com > wrote:
> 
> 
> I think that you're right. Foo<E> is basically Foo<E extends Object> and
> according to the rules String is assignable to Object.
> 
> Just to be clear, this test (that I added temporarily to CovariantTypesTest
> and ran just to make sure) fails (as I'd expect):
> 
> @Test
> public <E> void testFooStringAssignableFromFooE() {
> Type a = new TypeLiteral<Foo<String>>() {
> }.getType();
> Type b = new TypeLiteral<Foo<E>>() {
> }.getType();
> assertTrue(CovariantTypes.isAssignableFrom(a, b)); // kaboom
> }
> 
> But this test (the one under discussion) in BeanTypeAssignabilityRules
> succeeds (obviously or Weld's test suite would be broken):
> 
> @Test
> public <E> void testStringFooMatchesVariableFoo() throws Exception {
> Type stringFooType = new TypeLiteral<Foo<String>>() {
> }.getType();
> Type variableFooType = new TypeLiteral<Foo<E>>() {
> }.getType();
> Assert.assertTrue("Foo<String> should match Foo<E>",
> getRules().matches(stringFooType, variableFooType));
> }
> 
> So the rules CDI uses to do type matching (represented by
> BeanTypeAssignabilityRules ) are deliberately different from those used by
> JLS (represented by CovariantTypes ), right?

CovariantTypes/InvariantTypes are used by BeanTypeAssignabilityRules.
My understanding was that CDI dictates some rules, few of which are different or requiring some extra steps compared to pure JLS. That's why during evaluation you go through BeanTypeAssignabilityRules and whenever applicable you delegate to Covariant/InvariantTypes.

> 
> Best,
> Laird
> 
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