RFR: 8318160: javac does not reject private method reference with type-variable receiver [v6]

[Maurizio Cimadamore]

On Tue, 17 Oct 2023 23:21:26 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> right nice example thanks
>
> I made several experiments and decided for the approach in the last commit pushed. We will need an additional field in class `MethodResolutionContext` basically pointing to the current `LookupHelper` which can now decide if a symbol is inherited at a given site or not. Semantically there are not changes for any other method the only semantic change will be when we are looking for the method in a method reference.

I looked at the Resolve code some more, and also looked at the fix which likely caused this: 
https://bugs.openjdk.org/browse/JDK-8073842

So, `Resolve::findMethod` basically must NOT be called on a `site` Type that is a type variable. The original method resolution code enforces this in Attr::selectSym:

https://github.com/openjdk/jdk/blob/6fc35142315f1616fa35e415005c9483939c6920/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java#L4575

Note that here:

1. If we see that the qualifier is a type variable, we recurse on the upper bound
2. If we find that we ended up accessing a symbol that was private, replace the symbol with an access error
3. call `accessBase` on the final symbol

I think a similar fix should be possible for method references. That is, as we do now, normalize the `site` using `skipTypeVars`, but also save the original `site` somewhere (as we already do). Note that the LookupHelper class has an `access` method, which is used to validate the result of the lookup (e.g. typically call `accessBase` on it). Effectively, this is a post-resolution step, pretty much like the one in `Attr`, so we can add whatever logic we want there (I think replicating the code in `Attr`  - see steps above - would be the best).

So, I don't think we need to add the new `isInherited` method - just overriding `access` to do the same thing we do in `Attr::selectSym` should be enough (I hope)

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PR Review Comment: https://git.openjdk.org/jdk/pull/16210#discussion_r1363668229