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Widen look-ahead pending clause terms - #590
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This was referenced Jul 28, 2026
notatallshaw
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July 29, 2026 23:33
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 pending clause terms, both the candidate term and the decision-keyed blocker term, now widen through the same contract as decided-parent widening: a term may name any range that holds the same listed versions of its package. Adjacent gaps overlap, so consecutive rejected candidates coalesce into a single segment as the union is built, and the union stops accumulating a hole per rejection instead of growing quadratically.
The payoff shows up on conflict-heavy warm resolves. The
uv-issue-10344-airflow-py312scenario goes from roughly 19s to roughly 8s of wall time with an identical pin set.One behaviour changes as a result. When a widened candidate union covers a package's whole listing, the ask now conflicts by propagation rather than reporting no versions, so the terminal diagnostics walk also names candidate packages carried by look-ahead grouped clauses.