[ty] disallow negative narrowing on SubclassOf types#23598
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charliermarsh
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Feb 27, 2026
| reveal_type(x) # revealed: A | ||
| return | ||
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| reveal_type(x) # revealed: A | B |
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(So this shows B on main?)
Typing conformance resultsNo changes detected ✅ |
Memory usage reportMemory usage unchanged ✅ |
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carljm
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Feb 27, 2026
* main: [ty] Take myself out of the reviewer pool for the next few days (#23618) [ty] Fix bug where ty would think that a `Callable` with a variadic positional parameter could be a subtype of a `Callable` with a positional-or-keyword parameter (#23610) [`ruff`] Add fix for `none-not-at-end-of-union` (`RUF036`) (#22829) Bump cargo dist to 0.31 (#23614) [`pyflakes`] Fix false positive for names shadowing re-exports (`F811`) (#23356) [`fastapi`] Handle callable class dependencies with `__call__` method (`FAST003`) (#23553) [ty] Recurse into tuples and nested tuples when applying special-cased validation of `isinstance()` and `issubclass()` (#23607) Update typing conformance suite commit (#23606) [ty] Detect invalid uses of `@final` on non-methods (#23604) [ty] Move the type hierarchy request handlers to individual modules [ty] Wire up the type hierarchy implementation with the LSP [ty] Add routine for mapping from system path to vendored path [ty] Implement internal routines for providing the LSP "type hierarchy" feature [ty] Add some helper methods on `ClassLiteral` [ty] Move some module name helper routines to methods on `ModuleName` [ty] Bump version of `lsp-types` [ty] Refactor to support building constraint sets differently (#23600) [ty] Dataclass transform: neither frozen nor non-frozen (#23366) [ty] Add snapshot tests for advanced `invalid-assignment` scenarios (#23581) [ty] disallow negative narrowing on SubclassOf types (#23598)
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Summary
We can't negatively narrow on an
isinstanceorissubclasscheck against a variable of typetype[X], because at runtime the value of the variable could be a subclass ofX.Test Plan
Added mdtest.