Can't solve with dune package management since min ocaml version bumped to 5.2.0

[gridbugs]

Opam is still able to find a solution but dune cannot. This has been a problem since #3131. Reverting that PR and dune is able to find a solution, however it chooses ocaml.4.14.2. I'm investigating why dune doesn't choose a later version of ocaml.

[gridbugs]

The problem seems to be related to the river package which is pinned to a specific revision. Dune might be treating this pin differently from opam which has implications on constraints on the versions of other packages but I don't understand the full story yet. Removing river from the dependencies makes the problem go away.

[gridbugs]

In the pinned version of river (https://github.com/aantron/river#476dc945a908a69548bddd267f143a3e5d9c8a1a) there is a dependency on the package ocamlnet which depends on "ocaml" {>= "4.02" & < "5"} which explains why dune refused to choose a version of ocaml above 5. It doesn't explain why opam was able to find a solution. Did it ignore the pin? When I solve the project with opam I don't see a dependency on ocamlnet even though it claims to be using a pinned version of river, but maybe opam just takes the package source from the pin and ignores the package metadata (including dependencies)?. Not sure.

Anyway as long as ocaml.org depends on a pinned version of river with ocamlnet among its dependencies I think we should not constrain the minimum version of ocaml to > 5.

[yawaramin]

The pin was removed in #3178, the project is now depending on upstream river.