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

[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

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

Commit messages:
 - 8343286: Redundant cast in polymorphic method call

Changes: https://git.openjdk.org/jdk/pull/21914/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21914&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343286
  Stats: 29 lines in 7 files changed: 28 ins; 0 del; 1 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