RFR: 8343286: Missing unchecked cast warning in polymorphic method call [v3]

[Vicente Romero]

> 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

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' into JDK-8343286
 - fixing build error
 - Merge branch 'master' into JDK-8343286
 - fixing build error
 - 8343286: Redundant cast in polymorphic method call

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/21914/files
  - new: https://git.openjdk.org/jdk/pull/21914/files/34b5b020..5bfcf8ef

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21914&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21914&range=01-02

  Stats: 996 lines in 62 files changed: 572 ins; 306 del; 118 mod
  Patch: https://git.openjdk.org/jdk/pull/21914.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21914/head:pull/21914

PR: https://git.openjdk.org/jdk/pull/21914