regression: overflow evaluating the requirement

[BoxyUwU]

• https://crater-reports.s3.amazonaws.com/beta-1.82-1/beta-2024-09-05/gh/davedray.gatekeeper/log.txt

[INFO] [stdout] error[E0275]: overflow evaluating the requirement `Unique<(dyn scheduled_thread_pool::thunk::Invoke + Send + 'static)>: Send`
[INFO] [stdout]    --> http/src/routes.rs:219:10
[INFO] [stdout]     |
[INFO] [stdout] 219 |         .or(warp::path!("api" / "users" / Uuid / "permissions")
[INFO] [stdout]     |          ^^
[INFO] [stdout]     |
[INFO] [stdout]     = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`http`)
[INFO] [stdout] note: required because it appears within the type `Box<(dyn scheduled_thread_pool::thunk::Invoke + Send + 'static)>`

note: if the relevant team already accepted this breakage then this issue can be closed

[saethlin]

The suggestion to raise the recursion limit works, and also other crates in this workspace have already raised the recursion limit even further. And this is a regression using warp filters.

[lcnr]

The suggestion to raise the recursion limit works, and also other crates in this workspace have already raised the recursion limit even further. And this is a regression using warp filters.

Given this, I would accept this regression without looking into it myself, thanks @saethlin

cc @rust-lang/types unsure whether you think we should FCP close this or if this ping is enough?

[jackh726]

Probably a ping is enough - I am curious what caused the regression though? Just a bisection is probably fine. Not a blocker.

[GrigorenkoPV]

Bisects to #126024

[lcnr]

the old solver does not track recursion depth in cache entries, so if we have:

• evaluate T: Trait, requires depth m
• later evaluate U: Trait which, at depth n depends on T: Trait, with m + n being greater than the recursion limit. This overflows if we do not use the cache entry for T: Trait

If T: Trait is cached, we avoid the overflow. The new solver always tracks the recursion limit when using the global cache to avoid this kind of instability