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sarugaku / resolvelib

Resolve abstract dependencies into concrete ones
ISC License
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Allow resolution to skip backtracking #66

Closed TheKevJames closed 8 months ago

TheKevJames commented 3 years ago

This change is meant to support pypa/pip#9258, eg. to allow users to opt out of backtracking behaviour in cases where they would prefer to receive failure or conflict results immediately, for example in cases where they wish to use this resolver to help them improve their version pinning strategies.

The full explanation is on the linked PR, though I'm of course happy to accept more specific resolvelib-related feedback here as well!

uranusjr commented 3 years ago

I don’t think this requires a resolvelib change. To make the resolver to not backtrack, you can simply return only one candidate from find_matches().

TheKevJames commented 3 years ago

@uranusjr grabbing the relevant-to-this-repo part of my response https://github.com/pypa/pip/pull/9258#issuecomment-743474226 :

I think the difference between returning fewer options in find_matches() vs what I've done here by disabling backtracking comes down to debuggability, in my mind. By reducing the number of options in find_matches(), we are preventing the resolver from gathering the potential failure_causes from that first iteration of resolving which can be incredibly useful in debugging; by simply disabling backtracking we are allowing the tool to do the heavy lifting of finding the potentially compatible versions for us and offloading only the decision of how to resolve to the developer. If we instead return only a single option, the developer would not only need to determine how to resolve the issue but would additionally need to determine for themselves what the potential issue is in the first place.

Perhaps the flag is poorly named here, as per your comments in the other PR. Would renaming this more along the lines of attempt_automated_conflict_resolution, or the inverse of fail_fast_on_conflict, make more sense?