Build issue with `no_std`

[ralphtandetzky]

Common issues

Problem: The package causes builds to fail when building with #![no_std].

Quick solution: It looks like this has already been addressed in the commit 6169a5261b496b319be4daefc52e3f010b688e08"rand_distr: fix no_std build". It would be great if a patch would be released sometime soon.

Details: My crate fails to build in the CI when I try to update to rand 0.9.0 and rand_distr 0.5.0. See https://github.com/ralphtandetzky/num-quaternion/actions/runs/13338283033/job/37258123493?pr=129. Therefore, this is blocking updating the dependencies of my crate.

The reasons is that in no_std builds, f64 does not provide the method abs() by itself. Therefore, the line

use num_traits::Float;

is necessary to pull in the abs() method in the file src/utils.rs. This line was removed in the new major version 0.5.
This problem does not occur with rust 1.84, but apparently with all older versions of the rustc compiler.

[dhardy]

The mentioned commit is from 2021, very much prior to the v0.5 release.

Can you confirm whether using rand_distr from the git repo works by adding this to your Cargo.toml?

[patch.crates-io.rand_distr]
git = "https://github.com/rust-random/rand_distr.git"

[ralphtandetzky]

No, it does NOT work. Sorry, my mistake. Here's what I found: It looks like the line use num_traits::Float; has been removed in commit a855547 Replaces the Poisson rejection method implementation (#1560) three weeks ago. It was not added again afterwards (that happened a long time ago). Therefore, we would need a new fix. Would you like me to create a fix and send a pull request? I can make it so clippy won't complain about a seemingly unused import.

[dhardy]

Please do!

But I'm confused about why this fails for you: it appears to be the cargo build --no-default-features --features=rand build. But cargo build --no-default-features works locally. Is it because of our dev-dependencies? They don't look relevant.

Is there something we should add to our CI?

[dhardy]

BTW you don't need to care about this because small_rng doesn't add any dependencies or even much code:

features = ["small_rng"] # Needed only for testing. TODO: Move tests outside lib.rs and make this a development dependency

[ralphtandetzky]

Okay. Fixed it in PR #13. I also made some small additions to your CI script.