RFR: 8272564: Incorrect attribution of method invocations of Object methods on interfaces

[Jim Laskey]

On Wed, 18 Aug 2021 13:46:59 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> Consider these declarations:
> 
>     interface I {
>         public String toString();
>     }
>     interface J extends I {}
> 
> 
> There are two issues with the `toString` inherited from `I` into `J`:
> -`Trees.isAccessible(..., I.toString, J)` will return false, because `Resolve.isAccessible` will return false, because `Resolve.notOverriddenIn` returns false, because the `Object.toString` method is found as an implementation of `I.toString` in the context of `J`. This is unfortunate, because `Elements.getAllMembers(J)` will return `I.toString` as a member, not `Object.toString`, so any API client listing all members and then validating them using `Trees.isAccessible` will filter `toString` out. The proposed solution is to avoid using the methods from `java.lang.Object` as implementations of interface methods in `Resolve.notOverriddenIn`. (Interfaces don't inherit from `j.l.Object` per my understanding of JLS.)
> -as a slightly less problematic case, consider:
> 
> I i = null;
> i.toString(); //AST and classfile contain call to I.toString()
> J j = null;
> j.toString(); //AST and classfile contain call to j.l.Object.toString()
> 
> 
> I believe the second invocation should also preferably be a call to `I.toString()`, not a call to `j.l.Object.toString()`. The reason for this behavior is that in javac, interfaces have `j.l.Object` as a supertype, so method lookups over interfaces will look into `j.l.Object` before looking into the superinterfaces, and the concrete method will prevail over the super interface method found later. The proposal is, for interfaces, to only look into `j.l.Object` is a method is not found in the interface and its superinterfaces.

Marked as reviewed by jlaskey (Reviewer).

test/langtools/tools/javac/api/TestIsAccessible.java line 61:

> 59:             for (Element member : ct.getElements().getAllMembers(name)) {
> 60:                 if (!trees.isAccessible(s, member, (DeclaredType) name.asType())) {
> 61:                     trees.isAccessible(s, member, (DeclaredType) name.asType());

Why is this statement necessary?

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PR: https://git.openjdk.java.net/jdk/pull/5165