feat: Add support for no_std

[oschijns]

Hello, I made a first draft for adding no_std support for this crate.
I needed to add a few dependencies to replace some std types with no_std equivalents.
I tried to find a way to replace the thread_local!{BUCKETS} with something but I am unsure if what I did makes sense...

[finnbear]

Thanks for the PR! I think no_std would be great for bvh :)

[codecov]

Codecov Report

❌ Patch coverage is 46.15385% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.69%. Comparing base (8005e04) to head (87848f0).
⚠️ Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
src/flat_bvh.rs	0.00%	5 Missing ⚠️
src/bvh/bucket.rs	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
- Coverage   49.89%   49.69%   -0.21%     
==========================================
  Files          17       18       +1     
  Lines        1471     1479       +8     
==========================================
+ Hits          734      735       +1     
- Misses        737      744       +7     

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[oschijns]

I didn't check the CI, I will submit fixes this evening.

[finnbear]

Thank you! Apologies for taking longer than I said I would take for review.

[finnbear]

Code changes look great! Here's what remains, in my opinion:

• Fixing whatever clippy found ;) (but don't worry about code coverage)
• Adding a CI step to test with no_std, possibly like the simd feature's CI step
• Rebasing into a few, meaningful, logical commits. There should be a bias towards avoiding commits that undo previous commits (e.g. the temporary inclusion of hashbrown shouldn't be reflected in the final commits). It seems easiest, for this PR, to rebase all code changes into a single commit. Once done, request svenstaro's review.
• Writing a changelog entry, which can be a separate commit.

Thanks!

[oschijns]

Hello, I added a CI for testing builds without the std feature.
I would suspect that I don't need the matrix.os list since no-std imply I don't use OS's features.

[oschijns]

Since Rust 1.80 has been released more than a year ago, I guess it is fine to bump the version? It fixes the dependency resolution.

[svenstaro]

I'd be fine with that.

[svenstaro]

@finnbear do you wanna merge this?

[finnbear]

@svenstaro I'm in favor of merging as-is, yes :)

I see user-facing benefit from the diff, and the only user-facing risk I see is that a higher MSRV could force a rustc upgrade (but raising it is consistent with our stated policy). Diff code style and commit history looks good (not perfect but not something I have time to fix or enumerate as review comments at the moment).

[svenstaro]

I would like to see a mention of this new feature in the README so that users are aware it exists.

[oschijns]

Ok, I'll add it.

[svenstaro]

Sorry about the conflicts. Should be easy to fix though.

[oschijns]

Sorry about the conflicts. Should be easy to fix though.

No problem.

However there may still be issues with clippy this time

cargo clippy --all-targets --all-features -- -D warnings
    Checking bvh v0.11.0 (/media/oschijns/Projects/rust/bvh)
error[E0554]: `#![feature]` may not be used on the stable release channel
  --> src/lib.rs:81:32
   |
81 | #![cfg_attr(feature = "bench", feature(test))]
   |                                ^^^^^^^^^^^^^

error[E0554]: `#![feature]` may not be used on the stable release channel
  --> src/lib.rs:82:31
   |
82 | #![cfg_attr(feature = "simd", feature(min_specialization))]
   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0554`.
error: could not compile `bvh` (lib) due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
error: could not compile `bvh` (lib test) due to 2 previous errors

[svenstaro]

Almost there! Just tiny fixes.

[svenstaro]

LGTM! @finnbear any last comments?

[finnbear]

Reread the diff; LGTM too 👍

[svenstaro]

Cool! Thanks @oschijns

[oschijns]

Thank you for the crate and for the merge!
:)