Suggest this == obj instead of super.equals(obj) when the two are equivalent.

[copybara-service]

Suggest this == obj instead of super.equals(obj) when the two are equivalent.

(inspired by Marcono1234's google/guava#6780)

[Marcono1234]

Thanks @cpovirk!

If you have time and energy for this, do you think it would also make sense to cover super.hashCode actually calling Object.hashCode? This also seems to happen now and then (e.g. elastic/elasticsearch#100871 or netty/netty#13659).

[cpovirk]

You're welcome. It has found way more problems than I expected, so thanks!

hashCode had occurred to me at one point, but I'd set it aside without much thought. I should have reconsidered after seeing how prevalent the equals problems were. I'm seeing what that turns up now. If it's as good as I'd expect, I'll productionize it.

[cpovirk]

The hashCode check turns up a bunch of bugs (many in the same file as the equals bugs, unsurprisingly) though maybe with a relatively larger fraction of inadvisable but not necessarily buggy methods. For example:

return id == null ? super.hashCode() : id.hashCode();

There are also some false-positive examples similar to what I'd seen with equals, in which people do some bit of work before delegating to super.

The checker is probably still worth doing, but it's not a complete no-brainer, so I'll try to come back to this when I have more brain to spare.

[cpovirk]

Eh, it looks like those are (mostly? entirely?) in classes whose equals methods we'd also be flagging. And really, in both cases, I think it makes sense to inline the == or System.identityHashCode operation instead of hiding it behind a super call that obscures things. So I'll mail out the review and see what happens.

[Marcono1234]

Thanks a lot for extending the check and also for the extensive documentation!

[cpovirk]

(I just took a quick peek at super calls to Object.toString(), and they look less broken. I suspect that a few are bugs, but many look legitimate (e.g., delegating to super for prod builds but producing more verbose output for dev builds).)