Most recent stable version is not selected when using `"*"` in queries

[brendanzab]

Describe the bug opam-nix selects ocaml 5.0.0~rc1 over ocaml 5.0.0 when using ocaml-base-compiler = "*"

To Reproduce

• Clone https://github.com/brendanzab/language-garden.git and checkout https://github.com/brendanzab/language-garden/commit/97f9f2d460a5894b4b2adf0a1612aec902b7d4e0
• Check the ocaml version:

  $ nix develop --command ocaml --version
  The OCaml toplevel, version 5.0.0

• Apply the following diff:

  diff --git a/flake.nix b/flake.nix
  index 012f4aa..2134b1d 100644
  --- a/flake.nix
  +++ b/flake.nix
  @@ -72,7 +72,7 @@
       # when building the opam project with `opam-nix`.
       query = devPackagesQuery // {
         # Force the ocaml compiler to be taken from opam-repository:
  -        ocaml-base-compiler = "5.0.0"; # Fix for opam-nix choosing 5.0.0~rc1 over 5.0.0
  +        ocaml-base-compiler = "*";
       };
  
       # Package-specific derivation overrides.

• Check the ocaml version:

  $ nix develop --command ocaml --version
  The OCaml toplevel, version 5.0.0~rc1

Expected behavior opam-nix would select the most recent stable version when "*" is specified. Alternatively it would select the most recent unstable version (there are more recent versions of ocaml-base-compiler now).

Environment

• OS name + version: macOS 13.4.1
• Version of the code: e83bd1d949c5e330a49f89d394b51b744248e3ca

[balsoft]

ocaml-base-compiler = "*" just gets passed along to opam as --packages ocaml-base-compiler, which should select the latest version (to some definition of "latest"). I believe 5.0.0 is a release, and thus should be "stable"?

[brendanzab]

Ahh, wonder why it is not selecting it 😕 – the docs on version ordering are here.

The ~ character is special as it sorts even before the end of sequence (i.e. before anything shorter: "\~" sorts before "", "a\~b" before "a"). It's most convenient for pre-releases, allowing 1.0~beta to be before 1.0.

[balsoft]

Not sure what else you are expecting? It seems to be behaving according to the documentation.

[balsoft]

You might to be looking at the wrong version of opam-repository; mind that by default opam-nix uses the version pinned in flake.lock (at this point, it's 786c55fa77c37f07eceea7d6a9bec04d2225e302)

[brendanzab]

Not sure what else you are expecting? It seems to be behaving according to the documentation.

I would have expected it to select the most recent non-prerelease version (i.e. nothing after the tilde), based on what is on the pinned version of opam-repository. But perhaps I don’t understand opam versioning that well (I’m used to how it works with Cargo).

Maybe I should just set the compiler version explicitly to avoid this in the future, as opposed to relying on *?

As an aside, is there a good way to query what versions of a package in the local opam-repository? At the moment I have just been going into the github repository to check what is at the current commit pinned in my flake, but that seems a little round-about. I assume there’s probably some OCaml tool that can help?

You might to be looking at the wrong version of opam-repository; mind that by default opam-nix uses the version pinned in flake.lock (at this point, it's 786c55fa77c37f07eceea7d6a9bec04d2225e302)

I was looking at the commit of opam-repository that I pinned on my flake. Sorry, I probably should have mentioned that – I was planning to, but I must have forgot. In the commit I linked to it was https://github.com/ocaml/opam-repository/commit/8241abf97ddbcb63f614372f31abeb306312f33c. I guess I’m wondering if this is exposing an issue that is not obvious in the currently pinned version of opam-repository?