[ty] Avoid bypassing lazy constraints for Divergent#26288
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Typing conformance resultsNo changes detected ✅Current numbersThe percentage of diagnostics emitted that were expected errors held steady at 94.37%. The percentage of expected errors that received a diagnostic held steady at 89.00%. The number of fully passing files held steady at 94/134. |
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mtshiba
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## Summary #26288 fixed a crash by preventing `when_constraint_set_assignable_to_owned` from returning a trivial `always` result for top-level `Divergent` pairs. The underlying issue was that the owned fast path and the lazy relation checker could disagree: the fast path treated some `Divergent` assignability checks as always satisfied, while the lazy relation checker treated top-level `Divergent` as never assignable. This patch resolves the inconsistency in the relation checker instead. Unmaterialized `Divergent` is assignability-compatible in both eager and lazy assignability, while it is still not a subtype of arbitrary types and still must not be eliminated by redundancy/union simplification. With the lazy relation checker aligned with the fast path, we no longer need the top-level `Divergent` exclusion in `is_trivially_constraint_set_assignable_to`. The regression test from #26288 still passes, and the unit test now asserts that constraint-set assignability treats `Divergent` consistently. ## Test Plan unit test updated
charliermarsh
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Jun 24, 2026
## Summary This reverts #26163 and its follow-up changes in #26230, #26246, #26274, #26275, and #26316. The recursive nominal-growth recovery replaces a previous cycle result nested inside a specialization with `Divergent`. The follow-up regressions show that this local replacement is not structurally safe: multi-arm union recovery can lose stable arms, and variadic tuple growth can continue after replacement. Addressing those cases required increasingly shape-specific alignment and guards without a general way to establish correspondence between fixed-point iterations. This restores the cycle-recovery behavior from before #26163. The direct self-referential `TypeOf` case and the regression coverage for astral-sh/ty#3835 and astral-sh/ty#3838 continue to pass without the heuristic and are retained. We remove only the cases that no longer converge: `TypeOf` references nested in nominal specializations and the nested-iterable case from astral-sh/ty#3827. The independent `Divergent` constraint fixes from #26288 and #26334, including the regression coverage for astral-sh/ty#3836, are also retained.
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Summary
when_constraint_set_assignable_to_ownedavoids entering its tracked Salsa query when a relation appears to be unconditionally satisfied. The shortcut usedmaterialized_divergent_fallback().is_none()to guard the union and intersection cases, but an unmaterializedDivergentmarker also has no fallback.During recursive inference, that allowed the shortcut to return an always-satisfied constraint set for relations such as
Divergenttoint | Divergent. Lazy constraint-set assignability intentionally handles a top-levelDivergentdifferently, so bypassing the query could admit an inconsistent bound and eventually trigger a debug assertion in constraint solving.This keeps the exact-equality fast path, but routes every other relation involving a top-level
Divergentthrough the tracked query. It also adds direct coverage for union and dynamic relations alongside the original nested-loop reproducer:Closes astral-sh/ty#3836.