Rust Issue 87012 Test Case

This is a test case for rust-lang/rust#87012.

Usage

Follow https://blog.rust-lang.org/inside-rust/2020/02/25/intro-rustc-self-profile.html to install summary and crox. You'll also need a nightly build.

Once the prep work is done, just run ./test.sh and you'll get a the affected line (evaluate_obligation) from the summary and a Chrome-compatible profile.

For reference: with rustc 1.57.0-nightly (ac2d9fc50 2021-09-21) the evaluate_obligation took around 30% of the time.

Construction

There are two crates:

• helper_crate: This contains a bunch of async code that involves nested types and calls, like you could find in a larger application. The entire code has a single entrypoint.
• repro_crate: The actual reproducer that just uses a single entrypoint from helper_crate and uses it multiple times in an async-trait.

Observation

It seems that some trait evaluation work is not done while compiling helper_crate (e.g. the Send check that is required by async-trait because it marks the future as Send) and then must be done multiple times when compling repro_crate.