Allow same source git patches with different rev / branch, etc.

[0xdapper]

Problem

Currently if I wanted to override and patch dependency across workspace of a dependency https://github.com/owner/repo to branch b this does not work

[patch.'https://github.com/owner/repo']
baz = { git = 'https://github.com/owner/repo', branch = 'my-branch' }

because of the input validation here

cargo/src/cargo/core/registry.rs

Lines 363 to 371 in 1366225

	if *summary.package_id().source_id().canonical_url() == canonical {
	return Err(anyhow::anyhow!(
	"patch for `{}` in `{}` points to the same source, but \
	patches must point to different sources",
	dep.package_name(),
	url
	))
	.context(format!("failed to resolve patches for `{}`", url));
	}

Proposed Solution

Remove the validation or make an exception when the source is a git url?

Notes

No response

[weihanglo]

Semi-related: #10667

Source replacement for git URL doesn't support rev and branch.

[fralalonde]

Bumping this up, this is a blocker for private project development where forks are not an option. Patching a project to override a crate dependency with a different branch of the same repo would be the way to go but is impossible right now because of this URL check.

A solution would be to compare the whole package specification (including any tag, branch, commit clause) and block only if every field is the same.

I could start work on a PR for it if this solution makes sense and the interest is there.

[dimonomid]

I definitely agree that it should be supported in cargo properly, but just to mention a workaround in case it's useful to anyone: it's possible to trick cargo into thinking that it's a different repo by using a double slash in the URL, like this:

[patch.'https://github.com/owner/repo']
baz = { git = 'https://github.com/owner//repo', branch = 'my-branch' }

Cloning https://github.com/owner//repo is the same as cloning https://github.com/owner/repo, so it works.

[PixelDust22]

@dimonomid I have tried this on Windows and I would like to report that it did not work. Maybe this is a linux-only workaround?

[dimonomid]

I'm not a Windows expert and don't have it around to try it right now, but I didn't expect that it wouldn't work. Could you share what is the error message?

[juzpermsky]

@dimonomid I have tried this on Windows and I would like to report that it did not work. Maybe this is a linux-only workaround?

That's worked for me on windows, also with ssh paths.
Corrected workaround, with specifying ssh/https port in patching path:

[patch.'https://github.com/owner/repo']
baz = { git = 'https://github.com:443/owner/repo', branch = 'my-branch' }

[weihanglo]

Just found this is exactly the same issue as #5478. Close in favor of that.