After lengthy reviewing and tinkering i wasn't satisfied with the solution either so i came up with a different proposal, which while a bit radical i strongly believe to be a positive change for users:

Currently pinning a local vcs directory will override the opam files with whatever the version in the working directory is, regardless of whether or not --working-dir is given. I think this behaviour is too surprising to users. If they wish to use the working directory version then they can pass --working-dir explicitly. This also has the side-effect to simplify our code quite a lot which is always nice.

I've pushed the proposal as the fixup proposal commit above. The parent fixup commit implements a couple of cleanups (probably mostly redundant if the proposal is to be accepted), and i've also added a commit at the top to change the return type of OpamRepository.revision which shouldn't have had the version type.

What do you think?

Putting back the PR to its original state as the fix of #6408. I've opened #6418 to discuss default behaviour change and #6419 the part of the PR that contains the wip.