feature: depopt selection in the workspace

[rgrinberg]

Add a [deopts] field to allow users to select depopts.

The depopts are selected globally for all packages that list them. This is inline with how opam does things.

Fixes #11643

Signed-off-by: Rudi Grinberg me@rgrinberg.com

[Leonidas-from-XIV]

Apart from the typo it looks good and the test works really well. Could use a mention of the depopts field in the documentation.

What do you think about allowing something like :all to enable all depopts? I recently was wanting for this in OPAM but it doesn't support it such an option.

[rgrinberg]

What do you think about allowing something like :all to enable all depopts? I recently was wanting for this in OPAM but it doesn't support it such an option.

Turns out that such a thing isn't that simple to implement. The only way to determine all depopts is to first find a solution.

We could perhaps implement something that's close enough semantically by introducing a "depopts_required" mode. This would just merge depopt constraints into depends constraints for every package and solve. I don't know if that's going to work, but you're welcome to experiment if you have a use case for this.

[bnguyenvanyen]

Hi, thanks a lot for having implemented this.Is this not missing a mention in CHANGES.md, and a guard on the language version ?

[Alizter]

@bnguyenvanyen Since this is a package management related PR and package management is considered "experimental" until we have a full-release, we generally tend not to include changes in the changelog or add version guards. When package management is officially released, there will be backwards compatible changes but until then it allows us to change the implementation details and design without friction.

[bnguyenvanyen]

@Alizter Ok, thank you. I ask because we started using the depopts stanza (at Routine) and it broke downstream packages that did not have the correct dune version (because they're still using opam). We'll pin versions downstream for now I guess.