[jdk16] RFR: 8231461: static/instance overload leads to 'unexpected static method found in unbound lookup' when resolving method reference

[Maurizio Cimadamore]

On Tue, 12 Jan 2021 02:21:31 GMT, Vicente Romero <vromero at openjdk.org> wrote:

> This patch fixes the following issue, for code like:
> import java.util.function.*;
>  
> public class Test {
>     public String foo(Object o) { return "foo"; }
>     public static String foo(String o) { return "bar"; }
> 
>     public void test() {
>         Function<String, String> f = Test::foo;
>     }
> }
> javac is issuing an invalid method reference error even though the static method is applicable. This is due to a regression on the implementation of the following assertion on section 15.13.1 of the JLS 14:
> 
> If the first search produces a most specific method that is static , and the set
> of applicable methods produced by the second search contains no non- static
> methods, then the compile-time declaration is the most specified method of
> the first search.
> 
> Apart from fixing the mentioned regression, this patch also adds a debug feature for the compiler to print out the findings during the search for an applicable method reference. The information is printed out if a debug flag is passed to the compiler.
> 
> TIA

The debugging logic seems good, but I don't get how the fix is supposed to work, since it seems to replicate the behavior that's already there. I'm probably missing something.

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java line 3327:

> 3325:         @Override
> 3326:         ReferenceLookupResult unboundResult(ReferenceLookupResult boundRes, ReferenceLookupResult unboundRes) {
> 3327:             if (boundRes.isSuccess() && boundRes.sym.isStatic() &&

For consistency here I'd prefer to see `boundRes.hasKind(StaticKind.STATIC)` (which is set if the underlying symbol is static). E.g. I think the fix here is really adding the `isSuccess` part, not changing the static check.

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PR: https://git.openjdk.java.net/jdk16/pull/107