Java 9 ea154 javac compiler error - legit or bug?

[Vitaly Davidovich]

Hi Maurizio,

Thanks for the reply.  So you're saying the example using assignment
context shouldn't compile either? Also, the call to 'foo' is unchecked in
the wildcard argument, but it has a concrete type in the first argument.
Are you saying that any unchecked param results in return type erasure?

Thanks

On Wed, Feb 8, 2017 at 8:38 PM Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

> Hi,
> it seems like the behavior you observed started in b83 - as a result of
> this:
>
> https://bugs.openjdk.java.net/browse/JDK-8078093
>
> I believe the error is correct (although the diagnostic has always been
> broken since b83 in the 'verbose' mode - the non-verbose mode - w/o
> -Xdiags:verbose is fine). That is, the call to 'foo' is unchecked, so the
> return type should be erased. There seems to be an inconsistency in how
> javac handles this in method context compared to assignment context, and
> that needs to be looked at.
>
> Thanks
>
>
> Maurizio
>
>
>
> On 08/02/17 19:23, Vitaly Davidovich wrote:
>
> Hi all,
>
> Given the following code:
>
> import java.util.ArrayList;
> import java.util.Collection;
>
> public class Foo {
>     static <T> T foo(Class<T> c, Collection<? super T> baz) {
> return null;
>     }
>
>     static void bar(String c) {
>
>     }
>
>     @SuppressWarnings("unchecked")
>     public static void main(String[] args) {
> // this works
> bar(foo(String.class, new ArrayList<String>()));
>
> // this works with a warning
> String s = foo(String.class, new ArrayList());
> bar(s);
>
> // this causes an error on JDK9
> bar(foo(String.class, new ArrayList()));
>     }
> }
>
> javac 9-ea (build 9-ea+154) fails with this interesting error (on the last
> line in main, as the comments there indicate):
>
> Foo.java:23: error: method bar in class Foo cannot be applied to given
> types;
>                 bar(foo(String.class, new ArrayList()));
>                 ^
>   required: String
>   found: String
>   reason: argument mismatch; Object cannot be converted to String
> 1 error
>
> Java 8 compiles fine, and the other 2 lines compile in the same java 9
> build as well.
>
> Is this a javac bug or legit? It seems like a compiler error.  At a
> minimum, the diagnostic output "required String, found String" is confusing.
>
> Thanks
>
>
>
> --
Sent from my phone
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/compiler-dev/attachments/20170209/1f298e9b/attachment.html>