RFR: 8343286: Missing unchecked cast warning in polymorphic method call

[Joe Darcy]

On Tue, 5 Nov 2024 19:51:04 GMT, Vicente Romero <vromero at openjdk.org> wrote:

> Javac is not issuing a mandated unchecked cast warning for code like:
> 
> 
> import java.lang.invoke.VarHandle;
> 
> class VarHandleCast<V> {
>      VarHandle vh;
>      V method(Object obj) {
>          return (V)vh.getAndSet(this, obj);
>      }
> }
> 
> 
> according to the spec the return type inferred for this method polymorphic method should be Object see:
> 
> -  If the compile-time declaration for the method invocation is a signature polymorphic method, then:
> ...
>     – The compile-time result is determined as follows:
>         Otherwise, if the method invocation expression is the operand of a cast
>     expression (§15.16), the compile-time result is the erasure of the type of the
>     cast expression (§4.6).
> 
> javac is not doing the type erasure mandated by the spec which is what this PR is fixing
> 
> TIA
> 
> Note: I had to add some annotations to suppress warnings in java.base that were not being issued before due to the javac bug

Hi @vicente-romero-oracle , please file a CSR to evaluate the behavioral changes here. Thanks.

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PR Comment: https://git.openjdk.org/jdk/pull/21914#issuecomment-2458209273