Regression in Beta/Nightly: implementation of `Trait` is not general enough

[msrd0]

Code

I tried this code:

https://github.com/gotham-rs/gotham/tree/3da82b63e36db81f73f0d88b7610a3979c62289a/examples/handlers/simple_async_handlers_await

I expected to see this happen: Code compiles (as it does on stable: https://github.com/gotham-rs/gotham/actions/runs/3873554934/jobs/6603712754)

Instead, this happened: Code fails to compile (on beta: https://github.com/gotham-rs/gotham/actions/runs/3873554934/jobs/6603712995 and nightly: https://github.com/gotham-rs/gotham/actions/runs/3873554934/jobs/6603713263)

Version it worked on

It most recently worked on: 1.66.0 (69f9c33 2022-12-12)

Version with regression

1.67.0-beta.6 (51b0345 2022-12-31) and rustc 1.68.0-nightly (cc47b06 2023-01-08)

@rustbot modify labels: +regression-from-stable-to-beta

[albertlarsan68]

searched nightlies: from nightly-2022-10-29 to nightly-2022-12-10
regressed nightly: nightly-2022-12-10
searched commit range: 7632db0...dfe3fe7
regressed commit: 7701a7e (#105456)

bisected with cargo-bisect-rustc v0.6.5

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --access=github --start=1.66.0 --end=2022-12-10 -- build -p=gotham_examples_handlers_simple_async_handlers_await

@rustbot label +regression-from-stable-to-beta -regression-untriaged

[lqd]

@albertlarsan68 The rollup can itself be checked with these artifacts. I'm pretty sure it's going to be #105255 again.

[albertlarsan68]

• Remove UnsafetyState #105441
• Fix warning when libcore is compiled with no_fp_fmt_parse #105434
• CI: add missing line continuation marker #105433
• Use Symbol for the crate name instead of String/str #105423
• Add help for #![feature(impl_trait_in_fn_trait_return)] #105408
• Stop passing -export-dynamic to wasm-ld. #105405
• make retagging work even with 'unstable' places #105317
• Make nested RPIT inherit the parent opaque's generics. #105255
• kmc-solid: std::sys code maintenance #105120
• Detect long types in E0308 and write them to disk #104922

[albertlarsan68]

It is in fact #105255 that makes this error, cc @cjgillot @compiler-errors

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

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