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

[Vicente Romero]

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

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

Commit messages:
 - adding diagnostics tests
 - updating test
 - renaming test file
 - Merge branch 'master' into JDK-8231461
 - Merge branch 'master' into JDK-8231461
 - 8231461: static/instance overload leads to 'unexpected static method found in unbound lookup' when resolving method reference

Changes: https://git.openjdk.java.net/jdk16/pull/107/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16&pr=107&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8231461
  Stats: 300 lines in 8 files changed: 297 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/107.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/107/head:pull/107

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