Add lint to check if non-inlined local reexports have documentation

[GuillaumeGomez]

Fixes #43087.

Everything can't be checked directly from the newly added pass unfortunately since glob reexports have already been inlined at this point.

r? @notriddle

[rust-log-analyzer]

The job x86_64-gnu-llvm-13 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

Prepare all required actions
Getting action download info
Download action repository 'actions/checkout@v3' (SHA:ac593985615ec2ede58e132d2e21d2b1cbd6127c)
Download action repository 'rust-lang/simpleinfra@master' (SHA:b9dd95b10bcfe24d57bf54db874f81a7c8315a80)
Complete job name: PR (x86_64-gnu-llvm-13, false, ubuntu-20.04-xl)
git config --global core.autocrlf false
shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
env:
  CI_JOB_NAME: x86_64-gnu-llvm-13
---
---- [rustdoc] tests/rustdoc/multiple-import-levels.rs stdout ----

error: rustdoc failed!
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustdoc" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc/multiple-import-levels/auxiliary" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc/multiple-import-levels" "--deny" "warnings" "/checkout/tests/rustdoc/multiple-import-levels.rs"
stdout: none
--- stderr -------------------------------
error: doc comments on non-inlined reexports of local items are ignored
   |
12 |     /// 2
   |     ^^^^^
   |
   |
   = note: the documentation won't be visible because reexports don't have their own page
   = note: `-D rustdoc::unused-reexport-documentation` implied by `-D warnings`
help: try adding `#[doc(inline)]`
   |
13 |     #[doc(inline)] pub use crate::a::Type;
help: or move the documentation directly on the reexported item
   |
12 -     /// 2
12 +     
12 +     
   |

error: doc comments on non-inlined reexports of local items are ignored
   |
17 |     /// 3
   |     ^^^^^
   |
   |
   = note: the documentation won't be visible because reexports don't have their own page
help: try adding `#[doc(inline)]`
   |
18 |     #[doc(inline)] pub use crate::b::Type;
help: or move the documentation directly on the reexported item
   |
17 -     /// 3
17 +     
17 +     
   |

error: doc comments on non-inlined reexports of local items are ignored
   |
19 |     /// 4
   |     ^^^^^
   |
   |
   = note: the documentation won't be visible because reexports don't have their own page
help: try adding `#[doc(inline)]`
   |
20 |     #[doc(inline)] pub use crate::b::Type as Woof;
help: or move the documentation directly on the reexported item
   |
19 -     /// 4
19 +     

[GuillaumeGomez]

So, the failure is actually quite interesting because if a reexport is itself reexported, then it shouldn't emit a warning. This lint implementation will require a bit more work to take this into account. But before that, does this lint make sense or not?

[notriddle]

I think it does make sense to produce a warning in any case where actually using the doc comment is impractical.

[GuillaumeGomez]

We have some unused_attr lint emitted for doc comments in some places, but impractical, not that I know of.

[bors]

☔ The latest upstream changes (presumably #108934) made this pull request unmergeable. Please resolve the merge conflicts.

[anden3]

Hello @GuillaumeGomez! This PR has some merge conflicts, what's the status of it?

[GuillaumeGomez]

I need to reimplement it as described above. I keep this PR open as a reminder for future me when I have time. ^^'