Regression: false positive from unreachable_pub lint

[djc]

Code

I tried this code:

#![deny(unreachable_pub)]

pub use crate::builder::Foo;

mod builder {
    pub struct Foo(pub(crate) ());
}

I expected to see no output from the compiler.

Instead, this happened:

djc-2021 main test-rs $ cargo +nightly c
    Checking test-rs v0.1.0 (/Users/djc/src/test-rs)
error: unreachable `pub` item
 --> src/lib.rs:3:9
  |
3 | pub use crate::builder::Foo;
  | ---     ^^^^^^^^^^^^^^^^^^^
  | |
  | help: consider restricting its visibility: `pub(crate)`
  |

cargo-bisect-rustc ouptut

searched nightlies: from nightly-2022-09-22 to nightly-2022-09-27
regressed nightly: nightly-2022-09-25
searched commit range: 4a14677...3f83906
regressed commit: 6580010

This is a roll-up, #102109 seems the most likely culprit. cc @petrochenkov @oli-obk

bisected with cargo-bisect-rustc v0.6.4

Host triple: aarch64-apple-darwin
Reproduce with:

cargo bisect-rustc --start=2022-09-22 

@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged

[apiraino]

WG-prioritization assigning priority, probably a P-high since the lint malfunction is blocking valid code (iiuc)

@rustbot label -I-prioritize P-high T-compiler

[oli-obk]

@petrochenkov any ideas how to address this or should I start digging in to it

[petrochenkov]

In HIR pub use crate::builder::Foo; desugars into two items (import in type namespace and import in value namespace).
One of them is externally reachable and another is not (before #102109 both of them were incorrectly marked as externally reachable).

Code in compiler\rustc_lint\src\builtin.rs should somehow account for this desugaring and not report the pub as unnecessary if at least one of the imports is reachable.

[oli-obk]

I have been unable to fix this or apply a revert. @petrochenkov can you look at implementing this before the beta cutoff?

[petrochenkov]

Reverted in #103249.