Add [Float.]Array.{equal.compare}

[dbuenzli]

As the title says. Two notes for reviewers:

1. It seems that test_array.ml uses snapshot testing. I don't think it's that great for testing this kind of library code. So you may find the test structure a bit at odds (but if an assert fails the empty expectation fails).

2. There's a bit of tricky stuff around compare whose naked incarnation is used by Array.mem (and Float.Array.mem which uses Float.compare) which is bellow the compare addition. Since there's currently no dependency on Stdlib in array.ml I prefered not to use Stdlib.compare but rename it locally. If that's a dependency that is fine to introduce I can change that. Looking forward to Add a Repr module to the standard library #13755

P.S. Contributing functions to Array is painfull, between the label madness and Float.Array one spends most time bureaucratizing around and c&p code :-(

[lthls]

Since there's currently no dependency on Stdlib in array.ml I prefered not to use Stdlib.compare but rename it locally

Technically, there is: Stdlib is opened implictly, and things like invalid_arg and compare already introduce a dependency on Stdlib. But it's possible that using Stdlib.compare would make ocamldep see the dependency, which may or may not be an issue, so being conservative fells justified.

[dbuenzli]

But it's possible that using Stdlib.compare would make ocamldep see the dependency,

Yes that's what happend, a dependency on stdlib.cmi was added on stdlib__Array.* so I backed off (note however that stdlib_Float.* already has it, so I used it there).

[nojb]

LGTM, but I would avoid the exception.

A second approval from a core dev is needed to move forward with the PR.

[dbuenzli]

Thanks @nojb for the review. Your comments have been addressed.

[dbuenzli]

Not sure what happend with the CI of MSVC / clang-cl 64 bits:

List of failed tests:
    tests/compaction/test_compact_manydomains.ml

[nojb]

LGTM, modulo nits below

[gasche]

This looks nice to me as well.

Note: adding Array.compare may break code in the ecosystem that uses stdlib compare in an Array.(...) context, but this breakage would result in an type error and can be fixed in a backward-compatible way.

[dbuenzli]

Note: adding Array.compare may break code in the ecosystem that uses stdlib compare in an Array.(...)

At least on the sherlocode corpus of OCaml code and assuming this happens on a single line, this doesn't seem to happen.

[dbuenzli]

I think this could be merged.

[nojb]

Thanks for the ping!