Installing a package editably in one envs given diamond hierarchy forces all cases to be editable

[PeterJCLaw]

In a monorepo setup it's useful to be able to install base packages as editable (-e) in development, though in production you want to be able to install them fully into the site-packages so that you don't need to cart around the source tree separately from the python environment.

It looks like this mostly works for a basic environment hierarchy, however something isn't quite right when there's a diamond hierarchy involved:

      ┌──→ left ──↘
root ─┼──→ right ─→ dev
      └→ base-dev ↗

In the setup I have, a local package is referenced (non-editable) in root and thus transitively by both left and right. base-dev installs it editable. dev just pulls everything together for convenience.

I realise this is a slightly complicated setup, so I've put a reproduce at https://github.com/PeterJCLaw/pip-compile-multi-diamond-hierarchy-bug-demo.

In the failing case, all references to the common utils package are forced to be editable.

Removing either left.in or right.in from dev.in causes the result I want -- only things which depend on base-dev.in actually get forced to have the local package installed editable.

[peterdemin]

JFYI: I acknowledge the issue but I don't have bandwidth to fix it. You're welcome to propose a solution and I'll review the PR

[PeterJCLaw]

That's ok. Do you have any suggestions on why this might be working in the ordinary diamond hierarchy? (i.e: the case with only two, not three, legs)

[PeterJCLaw]

Hrm, removing --autoresolve also yields the result I'm after.

[PeterJCLaw]

Figured out why removing left.in or right.in from dev.in works -- because then the autoresolve logic can't find a common "sink" file which references all the other environments.

I think I now also understand why this is happening -- because when we do have a common sink and are using --autoresolve, the auto-resolving happens by setting a compatibilities constraints file for pip-compile which includes all the packages from the dev file, which is the editable version of the package.