check if we can get a rustc with debug assertions on CI

[matthiaskrgr]

There have been cases recently where clippy would crash if rustc was build with debug-assertions enabled.

#3628
rust-lang/rust#57298

To earlier catch regressions it might be helpful if we could get something like a rustc master tarball that has debug assertions enabled but I'm not sure if this exists.

[o01eg]

What about to use Ubuntu's PPA infrastructure?

[mati865]

I could create PPA but there is 2 GiB space quota so it could only keep 1 or 2 latest builds for LTS and latest Ubuntu release.
Additionally depending on the priority of the build it can take up to few hours to get build while rustc master provides builds very fast. We would run into issue when Ubuntu builds are blocking PRs because they are too old.

[ghost]

having rustc with debug assertions can crash firefox/servo too: servo/servo#22613
so, is this one more reason to have such a rustc ready for testing stuff with? ...

[mati865]

Maybe rust infra could provide builds with debug-assertions alongside normal builds if this is beneficial to many users.

[matthiaskrgr]

Hmm... I tried

rustup-toolchain-install-master --alt
cargo +2fba17fc972f89fe9165fbed77d2f0ad6d3e2174-alt test

but the alt rustc did not trigger any ICE on clippy d264e40 :/

[mati865]

Nightly builds have LLVM assertions enabled to catch bugs, nightly alt builds don't have them in order to improve performance.