Improved backwards compatibility hack for git URLs using dir=...

[GrahamDennis]

Motivation

In old versions of Nix, if you had a flake input like

inputs.foo.url = "git+https://foo/bar?dir=subdir";

it would result in a lock file entry like

 "original": {
   "dir": "subdir",
   "type": "git",
   "url": "https://foo/bar?dir=subdir"
 }

New versions of Nix remove ?dir=subdir from the url field, since the subdirectory is intended for FlakeRef, not the fetcher (and specifically the remote server), that is, the flakeref is parsed into

 "original": {
   "dir": "subdir",
   "type": "git",
   "url": "https://foo/bar"
 }

However, new versions of nix parsing old flake.lock files would pass the dir= query parameter in the "url" attribute to git, which will then complain.

Some mitigations for this issue were added before:

• 9f72d5b cleared all query attributes from file-scheme git URLs, but didn't touch other schemes (e.g. https or ssh). This PR removes the dir query parameter from all git URLs.
• d00682b ensured that newer nix versions wouldn't consider flake.lock files out-of-date that had these unnecessary dir=... attributes

Context

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[xokdvium]

@GrahamDennis sounds good in principle. Could you add a test though? A unit test in libflake-tests would be good I think.

[GrahamDennis]

@GrahamDennis sounds good in principle. Could you add a test though? A unit test in libflake-tests would be good I think.

This don't impact the Input you get by using inputFromAttrs or inputFromURL, it only impacts RepoInfo which is internal to git.cc and isn't (currently) exposed via git.hh to enable a test to be written in libfetchers-tests either.

The only way I can think to test this would be to write a functional test, but that would require using an ssh or http/s server for git and I believe all tests need to execute in a nix sandbox.

Happy to write a test, I'm just not sure how to do that in this case without refactoring to expose RepoInfo in git.hh.

[xokdvium]

I see. In that case this could probably go to fetch-git nixos test. There we have an actual forge (gitea) that should be enough for a test.

[edolstra]

Will merge this since it's simple enough, though a test would still be great.

[internal-nix-ci]

Successfully created backport PR for 2.32-maintenance:

• [Backport 2.32-maintenance] Improved backwards compatibility hack for git URLs using dir=... #14256