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Widen blocker terms to excluded membership - #604
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notatallshaw
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July 30, 2026 00:10
charliermarsh
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Aug 8, 2026
This is a partial port of a technique I am adopting in nab, I have been following @konstin's lead in astral-sh/pubgrub#75 and extending the approach into more places (notatallshaw/nab#357, notatallshaw/nab#590, notatallshaw/nab#592, notatallshaw/nab#604). This speeds up `uv lock` with `requires-python >= 3.8` over boto3 + awscli by ~20% wall time, and the largest accumulated range in the run drops from 287 segments to 2. `add_unavailable_version` records one singleton incompatibility per rejected version, so consecutive rejections never coalesce and the accumulated range grows a hole per version. This widens each singleton to the gap between its neighbors in the known versions, the same interval decided-version dependencies use. The win needs long runs of rejected versions. The main source is a Python floor below the ecosystem's support boundary: boto3 and awscli dropped 3.8 in April 2025 and now require >= 3.10, so a 3.8 floor rejects hundreds of releases in one run, while a 3.10 floor rejects almost nothing (14 rounds, 2 segments either way) and the change is a no-op. The first commit keys the pre-release hint on the requesting requirement instead of the derived set's bounds: widened bounds land on whatever the registry lists next, and a pre-release neighbor used to read as a pre-release marker nobody wrote. Rejection widening makes that routine, so the fix leads the series. The second commit merges unavailable versions that are causes of the same derivation, and the third is the widening itself. The fourth keeps the subsequent-index hint, which was suppressed whenever the set covered all versions; after widening that also covers "the index listed versions and none of them worked", which is the case the hint is for. The last two commits are #20809, merged in here so the error messages land as one change. With the widening, uv no longer asks for a version in a gap it created, so the `no_versions` incompatibility behind "only the following versions of X are available" is no longer created there, and steps that cross a gap stop following from the premises next to them. The fifth commit adds that clause back while the tree is reduced, on whichever cause rules the package out, or on the step itself when neither does. The sixth reports the one version a package has as that version rather than as a range over it, so a rejected `sphinx 7.2.6` reads `sphinx==7.2.6` and not `sphinx>=7.2.6`. Neither touches the solver. <details> <summary>MRE</summary> ```toml [project] name = "mre" version = "0.1.0" requires-python = ">=3.8" dependencies = ["boto3", "awscli"] ``` Max accumulated segments (287 on main, 2 with this PR; `uv.lock` identical): ```console $ uv lock --exclude-newer 2026-07-01 -v 2>&1 | grep 'Searching for a compatible version' | awk -F'|' '{print NF}' | sort -n | tail -1 ``` Wall (run without `-v`, which prints the accumulated ranges and dominates the time): ```console $ hyperfine --warmup 3 --min-runs 20 --prepare 'rm -f uv.lock' 'uv lock --exclude-newer 2026-07-01' ``` </details>
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Look-ahead blocker terms widen from the decided version's neighbor gap to the complement of the union of the dependency ranges the scanned candidates were rejected against. Each of those rejections fired because the blocker's version sat outside that candidate's range, so every blocker version outside the union repeats the same rejections and one clause excludes all of them. The widening falls back to the neighbor gap when any rejection in the group lacks a recorded range, or when the complement would not cover the group's own blocker.
pdm-skypilot-dvc, which timed out on every prior configuration, now resolves deterministically in 49s, and the conflict-heavyuv-issue-10344-airflow-py312drops roughly half its decisions on top of the span stack. The direction came from measuring that storm's conflicts: each one arrived already asserting and carried a single excluded version, so exclusion had to move into the clause supply rather than the search order.Stacks on #592.