Skip candidate not providing valid metadata by uranusjr · Pull Request #9264 · pypa/pip (original) (raw)

I had a galaxy-brain moment and realised the resolver does not really need to offer additional hooks for this. Since the candidate sequence is already implemented lazily, all we need to do is to check if the build fails during iteration, and skip the candidate when it happens.

Technical details (taken directly from the commit message):

This is done by catching InstallationError from the underlying distribution preparation logic. There are three cases to catch:

1. Candidates from indexes. These are simply ignored since we can potentially satisfy the requirement with other candidates.
2. Candidates from URLs with a dist name (PEP 508 or #egg=). A new UnsatisfiableRequirement class is introduced to represent this; it is like an ExplicitRequirement without an underlying candidate. As the name suggests, an instance of this can never be satisfied, and will cause eventual backtracking.
3. Candidates from URLs without a dist name. This is only possible for top-level user requirements, and no recourse is possible for them. So we error out eagerly.

The InstallationError raised during distribution preparation is cached in the factory, like successfully prepared candidates, since we don't want to repeatedly try to build a candidate if we already know it'd fail. Plus pip's preparation logic also does not allow packages to be built multiple times anyway.

Fix #9203, and also fix #9246 without changing with minimal change to the underlying build code.