While working on locking multiple platforms by default, I got an
infinite resolution loop in one of our resolver specs.
The culprit ended up being that when dealing with lockfile specs with
incomplete dependencies (spec appears in lockfile, but its dependencies
don't), those specs were not being properly expired and that tripped up
resolution.
The issue for some reason only manifests when dealing with multiple
lockfile platforms, that's why it only manifested when working on
locking multiple platforms by default.
4ca72913bb
Bundler is very conservative by default, trying to preserve versions
from the lockfile as possible, and never downgrading them. However, when
it runs into a resolution error, it still tries to find a valid
resolution.
This fallback behavior was too "brute-force" though, completely
unrestricting any gem found in the resolution conflict, and that could
lead to direct dependencies being downgraded in some edge cases.
Instead, unlock things a bit more carefully:
* First try unlocking fully pinned indirect dependencies, but leave a
lower bound requirement in place to prevent downgrades.
* Then try unlocking any fully pinned dependency, also leaving a lower
bound requirement in place.
* Finally completely unrestrict dependencies if nothing else worked.
7f55ed8302
Recent bugs fixed made me realize we were relying on state too much
here. We only need to keep incomplete specs to be able to expire them
and retry resolution without them locked. If we use a separate class, we
can do that more transparently and handle them just like we handle
"missing specs".
