[ty] Constraining a typevar with itself (possibly via union or intersection) #21273
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dcreager
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carljm and
sharkdp
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Diagnostic diff on typing conformance testsNo changes detected when running ty on typing conformance tests ✅ |
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carljm
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Nov 6, 2025
* main: (188 commits) [ty] Discover site-packages from the environment that ty is installed in (astral-sh#21286) [ty] Make special cases for `UnionType` slightly narrower (astral-sh#21276) Require ignore 0.4.24 in `Cargo.toml` (astral-sh#21292) [ty] Favour imported symbols over builtin symbols (astral-sh#21285) docs: revise Ruff setup instructions for Zed editor (astral-sh#20935) [ty] Update salsa (astral-sh#21281) [syntax-error]: no binding for nonlocal PLE0117 as a semantic syntax error (astral-sh#21032) [ty] Constraining a typevar with itself (possibly via union or intersection) (astral-sh#21273) [`ruff`] Fix false positives on starred arguments (`RUF057`) (astral-sh#21256) [ty] Simplify unions containing multiple type variables during inference (astral-sh#21275) [ty] Add `ty_server::Db` trait (astral-sh#21241) [ty] Refactor `Range` to/from `TextRange` conversion as prep for notebook support (astral-sh#21230) [ty] Fix playground crash when file name includes path separator (astral-sh#21151) [`refurb`] Fix false negative for underscores before sign in `Decimal` constructor (`FURB157`) (astral-sh#21190) [ty] Allow values of type `None` in type expressions (astral-sh#21263) Run codspeed benchmarks with `profiling` profile (astral-sh#21261) [ty] Update expected diagnostic count in benchmarks (astral-sh#21269) Avoid extra parentheses for long `match` patterns with `as` captures (astral-sh#21176) [ty] Update salsa (astral-sh#21265) [ty] `dict` is not assignable to `TypedDict` (astral-sh#21238) ...
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This PR carries over some of the
has_relation_tologic for comparing a typevar with itself. A typevar will specialize to the same type if it's mentioned multiple times, so it is always assignable to and a subtype of itself. (Note that typevars can only specialize to fully static types.) This is also true when the typevar appears in a union on the right-hand side, or in an intersection on the left-hand side. Similarly, a typevar is always disjoint from its negation, so when a negated typevar appears on the left-hand side, the constraint set is never satisfiable.(Eventually this will allow us to remove the corresponding clauses from
has_relation_to, but that can't happen until more of #20093 lands.)