Draft PR for exposing implied bounds in rustdoc JSON: https://github.com/rust-lang/rust/pull/148379
A concrete plan for how that new info turns into dozens of new lints covering many kinds of bounds
Linting ?Sized and 'static bounds turned out to be quite a bit more complex than I anticipated. The key issue is that seeing T: Foo + ?Sized does not guarantee that T can be unsized, since we might have Foo: Sized which renders the ?Sized relaxation ineffective. Similarly, seeing T: Foo might also non-obviously imply T: 'static via a similar implied bound.
Failure to correctly account for implied bounds would lead to catastrophic false-positives and false-negatives. For example, changing T: Foo to T: Foo + 'static could be a major breaking change or a no-op, depending on whether we have Foo: 'static (either directly or implicitly via other trait bounds).
We cannot determine implied bounds using information present in rustdoc JSON today, so the rustdoc team and I have been iterating on the best way to compute and include that information in rustdoc JSON. Assuming something similar to the aforementioned PR becomes part of rustdoc JSON, cargo-semver-checks stands to gain several dozen new lints covering these tricky cases over trait associated types, generic type parameters, and APIT/RPIT/RPITIT.
