nightly-2021-09-03: Compiler hang in project with a lot of axum crate routes

[paolobarbolini]

https://github.com/paolobarbolini/rustc-pr85868-regression

This small reproduction takes 20 seconds to cargo check on 50171c3, 45 seconds on 371f3cd.
On the real project, which is the one I run the bisection on, 50171c3 takes 1 minute, 371f3cd hangs for 12+ hours.

Bisection

searched nightlies: from nightly-2021-08-25 to nightly-2021-09-10
regressed nightly: nightly-2021-09-03
searched commit range: 50171c3...371f3cd
regressed commit: 371f3cd

bisected with cargo-bisect-rustc v0.6.0

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

cargo bisect-rustc 2021-08-25 --end 2021-09-10 --timeout 90 

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Bisected with rust-lang/cargo-bisect-rustc#135 😃

[SNCPlay42]

Looks like another case of #89195, with method chains creating big nested types like the reduction in that issue.

[apiraino]

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize +P-high

[jplatte]

FWIW axum 0.3.0 (released yesterday) is almost definitely not affected by this.

[shirshak55]

@jplatte It's because they used a box to fix this issue. So I don't think the underlying problem is solved?

[davidpdrsn]

@shirshak55 Thats correct.

[jplatte]

I didn't want to imply that the underlying problem is solved. Just thought this info would be interesting for people who are subscribed to this issue because they want to use axum + a recent Rust version.

[pnkfelix]

discussed in P-high review

closing as resolved, both due to axum-local workarounds first, and later due to #89195 being resolved by #90423