Ignore deprecation for items deprecated by the same attribute

[TimNN]

Whenever a node would be reported as deprecated:

• check if the parent item is also deprecated
• if it is and both were deprecated by the same attribute
• skip the deprecation warning

fixes#35128
closes#16490

r? @eddyb

[eddyb]

Not entirely sure, is this a good use of the lint hooks and DefIndex?
The need for a Vec is a bit sad - manually written visitors can get away with just regular stack recursion.
cc @Manishearth@llogiq@nikomatsakis

[Manishearth]

Remember that all the lints have the cost of a single visitor; they are threaded together. This cannot be done with arbitrary visitors. The lint hooks exist basically for this use case.

That said, can't we pull instead of push here? We can use parent nodes and walk up the node tree. The case of a lint being triggered is relatively rare, so paying the cost of a tree walk there isn't too bad.

[eddyb]

You mean we could use get_parent instead of a stack, and store a single NodeId?
I think that would work - the problem solved by the stack here is that not all NodeIds are in the map.

[Manishearth]

Why do we need to store anything?

Also, I thought that was fixed? Which nodes are missing from the map?

[TimNN]

@Manishearth: The cases I encountered where Paths: for example Foo and Bar in impl Foo for Bar or fn f<T: Foo>() {}, if I remember correctly.

[Manishearth]

Oh, I see. Hmm.

In that case,do what eddy suggested -- store a single node id, and dynamically walk up the tree from there on error.

[eddyb]

on error.

Not always in post_item?

[eddyb]

LGTM, modulo the two comments I've left.

[llogiq]

Yeah, walking up the tree isn't so bad if we can get away without allocation in the non-error case.

[eddyb]

@bors r+

[bors]

📌 Commit 65dafe0 has been approved by eddyb

[TimNN]

@eddyb could you r+ again, I had to fix a tidy failure.

[eddyb]

@bors r+

[bors]

📌 Commit 627b1e8 has been approved by eddyb

[bors]

⌛ Testing commit 627b1e8 with merge 4c02363...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-cargotest, auto-linux-64-cross-freebsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-no-mir, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-opt, auto-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-no-mir, auto-win-msvc-64-opt-rustbuild
Approved by: eddyb
Pushing 4c02363 to master...