Fix the 'no matching distributions' message being shown for installable packages

[2ykwang]

What does this PR do?

Fixes #14193

Uses find_all_candidates() so the no matching distributions available.... message is only shown when the project has no candidates.

PR Checklist:

• I agree to follow the PSF Code of Conduct.
• I have read and have followed the CONTRIBUTING.md file.
• I have added a news file fragment (or this PR does not need one).
• I have read and followed the AI_POLICY.md file, and if any AI tools were used, I have disclosed it below.

Assisted-by: Codex (review)

[2ykwang]

pre-commit.ci autofix

[sepehr-rs]

LGTM, thanks for the fix!

[ichard26]

Hmm, the "have no matching distributions available" note would still be printed if there no distributions available from an index (or find-links), but the package is given by an direct URL requirement.

Generally, whenever an "explicit requirement -- a requirement that forces a particular distribution at a specific URI -- is specified, the finder is irrelevant since the resolver must use the explicit distributions.

[2ykwang]

Generally, whenever an "explicit requirement -- a requirement that forces a particular distribution at a specific URI -- is specified, the finder is irrelevant since the resolver must use the explicit distributions.

ah, you're right. should names given by an explicit requirement be excluded from the hint then?

[ichard26]

I believe so. Not sure if there's an easy way to do that though.

[2ykwang]

How about something like this? We could collect the names of ExplicitRequirements in a separate set:

causes = set()
explicit_names = set()
for req, _ in e.causes:
    if isinstance(req, ExplicitRequirement):
        explicit_names.add(req.name)
    causes.add(req.name)
 

Finally, exclude ExplicitRequirement names from the _has_any_candidates() check:

no_candidates = {
    c for c in causes - explicit_names if not self._has_any_candidates(c)
}

[ichard26]

I'd have to dig into the resolver implementation further to be sure, but that looks generally OK...?

[notatallshaw]

I've been meaning to review this, I'll get round to it soonish.