Use targeted repositories that are only scanned explicitly

[zevisert]

This PR adds functionality for "targeted" repositories, which are not scanned during solving unless a package explicitly marks it as a source.

Example:

[[tool.poetry.source]]
name = "slow"
url = "https://foo.bar/simple/"
targeted = true

[tool.poetry.dependencies]
python = "^3"
your_package = { version = "^1", source="slow" }

Pull Request Check List

Resolves: #4035

• Added tests for changed code.
• Updated documentation for changed code.

[zevisert]

I haven't yet added a test to confirm that solving doesn't communicate with a targeted source unless explicitly requested. The tests started to look pretty complicated with all of the MockRespository functionality, so I thought it best to first check if there's interest in merging this PR at all.

[neersighted]

I'm not sure this is the approach we are going to take -- it's generally agreed that the current design is poor, but we would like to make a breaking change and improve it instead of tacking on more variant settings that increase the difficulty in reasoning about repositories. I would suggest joining the Discord server to discuss this with the core team, or creating an issue to talk about a new design for repositories.

I'm going to close this for now as this won't get merged in its current form -- feel free to re-open if suggestions for a new design occur and they crystalize into code, however.

[zevisert]

No problem, the code changes here were mostly just hacks to get the idea somewhat demonstrable. I agree with that sentiment tacking on more hacks is not the way to go!

🚀

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.