Add _post methods for blocks and crates

[llogiq]

This fixes #31512 for me.

A bit of explanation: I want to have check_block_post(&mut self, &Context, &Block) and check_crate_post(&mut self, &Context, &Crate) methods in both early and late lint passes. Ideally we'd have _post methods for all operations that walk, but this'll do for now.

@Manishearth r?

[rust-highfive]

r? @nikomatsakis

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[llogiq]

r? @Manishearth – I always forget which way 'round...

[Manishearth]

Could we have one for items too? That sounds like another logical thing to have a post-check for.

[llogiq]

Sure. I've got the commit here, but my notebook network is flaky. Will commit soon.

[llogiq]

@Manishearth done.

[Manishearth]

r=me, but also asking @eddyb for a second opinion

[eddyb]

I think we should try to experiment with a way to avoid combinatoric explosion, perhaps trait Check<T> with e.g. impl Check<Expr> for MyLint, but I don't see how this could be done cleanly without specialization (same goes for our visitors and folders btw).

[Manishearth]

That's an interesting idea, but I don't think combinatoric explosion can happen here, or that such changes need to be made here often.

An eventual new design for lint passes would be nice though. Not sure if we need it right now.

[Manishearth]

@bors r+

[bors]

📌 Commit d483a6e has been approved by Manishearth

[llogiq]

FWIW, I don't think we get combinatoric explosion here. Worst (or best, depending on how you look at it) case we have an entry/exit (or check/post in our current nomenclature) for each node that contains other nodes.

[llogiq]

There is some duplicate error messages in the compiletest output. I doubt it has something to do with the new methods, as there is nothing that uses them yet.

@bors retry

[oli-obk]

this should be check_item_post

[llogiq]

Thanks, @oli-obk ! Good catch.

[Manishearth]

@bors r+

[bors]

📌 Commit a270b7b has been approved by Manishearth

[bors]

⌛️ Testing commit a270b7b with merge 5801991...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-mac-ios-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt