The `git://` flake-URL type doesn't work

[iFreilicht]

Describe the bug

The docs on flake references give a few examples for how the git:// URL type can be used. Two of them don't work:

• git:/home/user/sub/dir
• git://github.com/edolstra/dwarffs?ref=unstable&rev=e486d8d40e626a20e06d792db8cc5ac5aba9a5b4

Steps To Reproduce

Local git repo:

$ file /Users/feuh/repos/nixpkgs
/Users/feuh/repos/nixpkgs: directory
$ nix shell git:/Users/feuh/repos/nixpkgs#python3
ssh: Could not resolve hostname git: nodename nor servname provided, or not known
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
warning: could not read HEAD ref from repo at 'git:/Users/feuh/repos/nixpkgs', using 'master'
ssh: Could not resolve hostname git: nodename nor servname provided, or not known
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
error:
       … while fetching the input 'git:/Users/feuh/repos/nixpkgs'

       error: program 'git' failed with exit code 128

Remote git repo:

$ nix shell git://github.com/edolstra/dwarffs
fatal: unable to connect to github.com:
github.com[0: 140.82.121.3]: errno=Operation timed out

warning: could not read HEAD ref from repo at 'git://github.com/edolstra/dwarffs', using 'master'
fatal: unable to connect to github.com:
github.com[0: 140.82.121.3]: errno=Operation timed out

error:
       … while fetching the input 'git://github.com/edolstra/dwarffs'

       error: program 'git' failed with exit code 128

Manually specifying (or omitting) the file, ssh or https prefixes works:

$ nix shell git+file:/Users/feuh/repos/nixpkgs#python3
$ nix shell /Users/feuh/repos/nixpkgs#python3
$ nix shell git+ssh://github.com/edolstra/dwarffs
$ nix shell git+https://github.com/edolstra/dwarffs

Expected behavior

I would expect all of these to work.

nix-env --version output

nix-env (Nix) 2.18.1

Additional context

While testing this, I also found that nix shell git+https://github.com/NixOS/nixpkgs has zero output for a long time while it's downloading. That would be a separate issue, though.

Priorities

Add 👍 to issues you find important.

[thufschmitt]

I think requesting the +transport bit is a good approach. But we should indeed fix the manpage examples

[iFreilicht]

@thufschmitt What do you mean by "requesting" in this context? Shouldn't it be possible to automatically detect the transport? At least local filesystem vs remote, and in the remote case ssh is probably preferred as it allows a shallow clone (though I don't know of that is used right now).

Or am I misunderstanding your point?

[thufschmitt]

Discussed in Nix team meeting on 2023-12-19 (sorry for the delay in reporting that 😬 )

Having git:// is ambiguous, it would be better to ask users to explicitly specify the transport (git+https, git+ssh, git+file, etc..).

There's two improvements that can be made though:

1. Fix the doc to remove the wrong examples
2. Give a better error message when people enter plain git:// urls

- @regnat: Explicitly requesting a transport in the url scheme seems fine - @roberth: We need to fix the docs though

Decision:

• For now, just fix the docs. We're not stabilizing that right now any way.
• Also improve the error message when using the git:// scheme
• Removed from the fetchTree milestone because we're not taliking about stabilizing URLs right now

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-12-15-nix-team-meeting-minutes-112/38155/1

[lf-]

Hey, this is actually busted because git:// is the legacy git protocol which GitHub has removed with prejudice several years ago. The examples do not work, not because of a regression, but because the legacy Git protocol is dead.