False-positives due to renaming re-exports + name collisions in the same crate

[obi1kenobi]

Our cargo semver-checks CI steps currently fail for libp2p-dcutr and libp2p-relay, even though neither of them merged any changes since the last libp2p v0.50.0 release.

• libp2p-dcutr https://github.com/libp2p/rust-libp2p/actions/runs/3576177811/jobs/6013685638
• libp2p-relay https://github.com/libp2p/rust-libp2p/actions/runs/3576177811/jobs/6013686091

Originally posted by @mxinden in libp2p/rust-libp2p#2647 (comment)

I was able to replicate the issue locally. The generated rustdoc for libp2p-dcutr at first glance doesn't seem to have anything out of place. I spot-checked one of the enums and variants that reported an error, and they were present in both the baseline and current rustdoc with identical IDs and reasonable-looking data.

This issue needs further triage.

[obi1kenobi]

Unfortunately, I found that this is because of a combination of renaming re-exports causing confusion between multiple enums with the same name. For example, a pub enum UpgradeError exists in all of:

protocols/dcutr/src/protocol/outbound.rs
protocols/dcutr/src/protocol/inbound.rs
protocols/dcutr/src/behavior.rs

The false-positives happen because the lint tries to match up all the variants across different enums, which obviously isn't going to do the right thing.

cargo-semver-checks doesn't currently handle re-export renames (and re-exports are already tricky because of the possibility of having infinitely many re-exported names for each item: #152 ), so this isn't a trivial fix.

That said, it's still important to fix and this should be sufficient motivation to come up with a permanent solution to the re-exports problem :)

[obi1kenobi]

It's tempting to use the canonical_path edge instead of importable_path edge in the affected lints. Right now, this wouldn't work, since re-exported items do not currently have a canonical_path available, since that path uses the rustdoc index information which currently does not include re-exported items.

Relevant rustdoc issues:
rust-lang/rust#93522
rust-lang/rust#99513