Support Direct URL editable requirements

[ichard26]

This is crucial for the deprecation of non-bare egg URL fragments as they used to be the sole way to request an extra for a VCS editable install.

I've also removed all references to egg fragments from the user docs and added further explanation of the Direct URL form in the VCS support topic.

Getting the error handling right was a pain. That's why I extracted the two parsing flows into their own functions.

Towards #13157.
Towards #1289.
Supersedes #9471.

[ichard26]

Ugh, why is everything filled with so many exceptions and undocumented extensions. There is a backwards compatibility break here. I'll fix it, but I do want to take a closer look at why it's happening.

[notatallshaw]

@ichard26 is this ready for review? Hard to tell from your last comment.

[ichard26]

@notatallshaw short of the one outstanding documentation change that's noted above, this is indeed ready for review.

[sbidoul]

Thanks for this work @ichard26. I made a pass on this and did a few tests. Everything works as I expected.

A few minor comments, some of which for possible followups.

I noticed a remaining #egg mention in a warning message:

pip install -e "pkgb @ file://$PWD/pkga"

WARNING: Generating metadata for package pkgb produced metadata for project name pkga. Fix your #egg=pkgb fragments.

[sbidoul]

Note: it could be convenient to support pkgname[extras] @ ./localdir as an alternative to ./localdir[extras]. But that can be discussed separately.

[ichard26]

I'd rather not add extensions to standard requirement syntax, but yes, this would be a follow up.

[sbidoul]

What do you mean with this comment?

[ichard26]

With the extraction of _parse_pip_syntax_editable(), now every editable requirement is checked that there is a known project name. This is problematic for local editable reqs like -e . or -e /local/path. Previously these cases would return early in parse_editable() skipping this check, but now they fail it. However, pip can and will infer the project name for local file URIs so we skip the check if that's the case.

[ichard26]

@notatallshaw I do want to get this into the 25.3 release. I'll aim to get this updated by EOD tomorrow.

[notatallshaw]

@ichard26 👍, I'll try and do a quick pass over this today, but as it's so far outside my expertise it's unlikely I'll have any additional comments.

[sbidoul]

Don't forget to postpone the #egg deprecation:

pip/src/pip/_internal/models/link.py

Lines 476 to 482 in 4dd68aa

	if not self._project_name_re.match(project_name):
	deprecated(
	reason=f"{self} contains an egg fragment with a non-PEP 508 name.",
	replacement="to use the req @ url syntax, and remove the egg fragment",
	gone_in="25.3",
	issue=13157,
	)

At some point this warning will also need addressing to be complete:

pip/src/pip/_internal/req/req_install.py

Lines 424 to 430 in 4dd68aa

	logger.warning(
	"Generating metadata for package %s "
	"produced metadata for project name %s. Fix your "
	"#egg=%s fragments.",
	self.name,
	metadata_name,
	self.name,

[notatallshaw]

Thanks @ichard26 ! I'll follow up in a moment with a PR that bumps any remaining gone_ins.