[ty] Require subtyping for transitive constraint pivots#25778
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[ty] Require subtyping for transitive constraint pivots#25778charliermarsh wants to merge 2 commits into
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Typing conformance resultsNo changes detected ✅Current numbersThe percentage of diagnostics emitted that were expected errors held steady at 92.23%. The percentage of expected errors that received a diagnostic held steady at 87.42%. The number of fully passing files held steady at 92/134. |
Memory usage reportSummary
Significant changesClick to expand detailed breakdownsphinx
prefect
|
|
| Lint rule | Added | Removed | Changed |
|---|---|---|---|
invalid-assignment |
0 | 1 | 0 |
invalid-return-type |
0 | 0 | 1 |
| Total | 0 | 1 | 1 |
Large timing changes:
| Project | Old Time | New Time | Change |
|---|---|---|---|
pytest-robotframework |
0.16s | 0.28s | +69% |
Flaky changes detected. This PR summary excludes flaky changes; see the HTML report for details.
Raw diff:
paasta (https://github.com/yelp/paasta)
- paasta_tools/tron_tools.py:573:16 error[invalid-return-type] Return type does not match returned value: expected `dict[str, FieldSelectorConfig]`, found `dict[str | FieldSelectorConfig, FieldSelectorConfig | dict[str, str]]`
+ paasta_tools/tron_tools.py:573:16 error[invalid-return-type] Return type does not match returned value: expected `dict[str, FieldSelectorConfig]`, found `dict[str, FieldSelectorConfig | dict[str, str]]`
prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/runtime/flow_run.py:70:5 error[invalid-assignment] Object of type `dict[<class 'bool'> | <class 'int'> | <class 'float'> | ... omitted 3 union elements, ((x) -> Unknown) | <class 'int'> | <class 'float'> | <class 'str'> | ((dt: str) -> datetime)]` is not assignable to `dict[type[int | float | str | Unknown] | <class 'NoneType'>, (Any, /) -> Any]`
Merging this PR will degrade performance by 4.22%
Warning Please fix the performance issues or acknowledge them on CodSpeed. Performance Changes
Tip Investigate this regression with the CodSpeed MCP and your agent. Comparing 
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Summary
When building sequent maps for constraints on different type variables, we use materialized bounds as pivots to derive transitive relationships. We previously accepted a pivot when those bounds were assignable. Unrelated classes with dynamic bases are mutually assignable, so this connected otherwise independent invariant type variables and caused the constraint set in the issue reproducer to grow combinatorially.
This changes those pivot checks to require subtyping. Because the bounds can themselves contain type variables, the new check uses constraint-set-aware subtyping rather than the ordinary subtype relation. Constraint-set type-variable handling is now an independent mode on
TypeRelationChecker, so it can be combined with either subtyping or assignability; the mode is also included in relation and signature recursion keys so cached results are not shared across comparison modes.In a local benchmark of the issue reproducer, check time fell from 14.5 seconds with constraint-set assignability to 46 milliseconds with constraint-set subtyping.
Closes astral-sh/ty#3607.