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move typevar arms around

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This commit is contained in:
Douglas Creager 2025-08-27 14:53:00 -04:00
parent 19c421a27b
commit b1a987318f
3 changed files with 71 additions and 93 deletions
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2
crates/ty_python_semantic/resources/mdtest/generics/legacy/functions.md
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@ -279,7 +279,7 @@ T = TypeVar("T", int, str)
def same_constrained_types(t1: T, t2: T) -> T: def same_constrained_types(t1: T, t2: T) -> T:
# TODO: no error # TODO: no error
# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `T@same_constrained_types` and `T@same_constrained_types`" # error: [invalid-return-type] "Return type does not match returned value: expected `T@same_constrained_types`, found `int | Unknown`"
return t1 + t2 return t1 + t2
``` ```

2
crates/ty_python_semantic/resources/mdtest/generics/pep695/functions.md
View file

@ -246,7 +246,7 @@ methods that are compatible with the return type, so the `return` expression is
```py ```py
def same_constrained_types[T: (int, str)](t1: T, t2: T) -> T: def same_constrained_types[T: (int, str)](t1: T, t2: T) -> T:
# TODO: no error # TODO: no error
# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `T@same_constrained_types` and `T@same_constrained_types`" # error: [invalid-return-type] "Return type does not match returned value: expected `T@same_constrained_types`, found `int | Unknown`"
return t1 + t2 return t1 + t2
``` ```

160
crates/ty_python_semantic/src/types.rs
View file

@ -1568,85 +1568,6 @@ impl<'db> Type<'db> {
Type::NonInferableTypeVar(rhs_bound_typevar), Type::NonInferableTypeVar(rhs_bound_typevar),
) if lhs_bound_typevar == rhs_bound_typevar => ConstraintSet::from(true), ) if lhs_bound_typevar == rhs_bound_typevar => ConstraintSet::from(true),
// A fully static typevar is a subtype of its upper bound, and to something similar to
// the union of its constraints. An unbound, unconstrained, fully static typevar has an
// implicit upper bound of `object` (which is handled above).
(Type::NonInferableTypeVar(bound_typevar), _)
if bound_typevar.typevar(db).bound_or_constraints(db).is_some() =>
{
match bound_typevar.typevar(db).bound_or_constraints(db) {
None => unreachable!(),
// Verify that the upper bound satisfies the relation. (If it does, than any
// subtype of the upper bound will too.) Also add a safety constraint that
// ensures that the typevar specializes to a subtype of the upper bound.
Some(TypeVarBoundOrConstraints::UpperBound(bound)) => {
ConstraintSet::constrain_typevar(db, bound_typevar, Type::Never, bound)
.implies(db, || {
bound.has_relation_to_impl(db, target, relation, visitor)
})
}
Some(TypeVarBoundOrConstraints::Constraints(constraints)) => {
constraints.elements(db).iter().when_all(db, |constraint| {
// Note that constrained typevars must specialize to _exactly_ one of the
// constraints, not to a _subtype_ of one.
ConstraintSet::constrain_typevar(
db,
bound_typevar,
*constraint,
*constraint,
)
.implies(db, || {
constraint.has_relation_to_impl(db, target, relation, visitor)
})
})
}
}
}
// If the typevar is constrained, there must be multiple constraints, and the typevar
// might be specialized to any one of them. However, the constraints do not have to be
// disjoint, which means an lhs type might be a subtype of all of the constraints.
(_, Type::NonInferableTypeVar(bound_typevar))
if !bound_typevar
.typevar(db)
.constraints(db)
.when_some_and(|constraints| {
constraints.iter().when_all(db, |constraint| {
ConstraintSet::constrain_typevar(
db,
bound_typevar,
*constraint,
*constraint,
)
.implies(db, || {
self.has_relation_to_impl(db, *constraint, relation, visitor)
})
})
})
.is_never_satisfied() =>
{
// TODO: The repetition here isn't great, but we really need the fallthrough logic,
// where this arm only engages if it returns true (or in the world of constraints,
// not false). Once we're using real constraint sets instead of bool, we should be
// able to simplify the typevar logic.
bound_typevar
.typevar(db)
.constraints(db)
.when_some_and(|constraints| {
constraints.iter().when_all(db, |constraint| {
ConstraintSet::constrain_typevar(
db,
bound_typevar,
*constraint,
*constraint,
)
.implies(db, || {
self.has_relation_to_impl(db, *constraint, relation, visitor)
})
})
})
}
(Type::TypeVar(_), _) if relation.is_assignability() => { (Type::TypeVar(_), _) if relation.is_assignability() => {
// The implicit lower bound of a typevar is `Never`, which means // The implicit lower bound of a typevar is `Never`, which means
// that it is always assignable to any other type. // that it is always assignable to any other type.
@ -1656,9 +1577,6 @@ impl<'db> Type<'db> {
ConstraintSet::from(true) ConstraintSet::from(true)
} }
// `Never` is the bottom type, the empty set.
(_, Type::Never) => ConstraintSet::from(false),
(Type::Union(union), _) => union.elements(db).iter().when_all(db, |&elem_ty| { (Type::Union(union), _) => union.elements(db).iter().when_all(db, |&elem_ty| {
elem_ty.has_relation_to_impl(db, target, relation, visitor) elem_ty.has_relation_to_impl(db, target, relation, visitor)
}), }),
@ -1686,12 +1604,74 @@ impl<'db> Type<'db> {
}) })
} }
// Other than the special cases checked above, no other types are a subtype of a // A non-inferable typevar must satisfy the relation for every possible specialization.
// typevar, since there's no guarantee what type the typevar will be specialized to. (Type::NonInferableTypeVar(bound_typevar), _) => {
// (If the typevar is bounded, it might be specialized to a smaller type than the match bound_typevar.typevar(db).bound_or_constraints(db) {
// bound. This is true even if the bound is a final class, since the typevar can still // Verify that the upper bound satisfies the relation. (If it does, than any
// be specialized to `Never`.) // subtype of the upper bound will too.)
(_, Type::NonInferableTypeVar(_)) => ConstraintSet::from(false), None => {
let bound = Type::object();
ConstraintSet::constrain_typevar(db, bound_typevar, Type::Never, bound)
.implies(db, || {
bound.has_relation_to_impl(db, target, relation, visitor)
})
}
Some(TypeVarBoundOrConstraints::UpperBound(bound)) => {
ConstraintSet::constrain_typevar(db, bound_typevar, Type::Never, bound)
.implies(db, || {
bound.has_relation_to_impl(db, target, relation, visitor)
})
}
// Verify that each constraint satisfies the relation. (Note that constrained
// typevars must specialize to _exactly_ one of the constraints, not to a
// _subtype_ of one.)
Some(TypeVarBoundOrConstraints::Constraints(constraints)) => {
constraints.elements(db).iter().when_all(db, |constraint| {
ConstraintSet::constrain_typevar(
db,
bound_typevar,
*constraint,
*constraint,
)
.implies(db, || {
constraint.has_relation_to_impl(db, target, relation, visitor)
})
})
}
}
}
(_, Type::NonInferableTypeVar(bound_typevar)) => {
match bound_typevar.typevar(db).bound_or_constraints(db) {
// There is no guarantee which type an unconstrained typevar might specialize
// to. Never (which is checked above) is the only type that is a subtype of any
// specialization.
None | Some(TypeVarBoundOrConstraints::UpperBound(_)) => {
ConstraintSet::from(false)
}
// A constrained typevar, on the other hand, does have a fixed set of types
// that it can specialize to, so we can check them all exhaustively.
Some(TypeVarBoundOrConstraints::Constraints(constraints)) => {
constraints.elements(db).iter().when_all(db, |constraint| {
ConstraintSet::constrain_typevar(
db,
bound_typevar,
*constraint,
*constraint,
)
.implies(db, || {
self.has_relation_to_impl(db, *constraint, relation, visitor)
})
})
}
}
}
// `Never` is the bottom type, the empty set.
// Other than one unlikely edge case (TypeVars bound to `Never`),
// no other type is a subtype of or assignable to `Never`.
(_, Type::Never) => ConstraintSet::from(false),
(_, Type::TypeVar(typevar)) (_, Type::TypeVar(typevar))
if relation.is_assignability() if relation.is_assignability()
@ -1968,9 +1948,7 @@ impl<'db> Type<'db> {
// Other than the special cases enumerated above, `Instance` types and typevars are // Other than the special cases enumerated above, `Instance` types and typevars are
// never subtypes of any other variants // never subtypes of any other variants
(Type::NominalInstance(_) | Type::NonInferableTypeVar(_), _) => { (Type::NominalInstance(_), _) => ConstraintSet::from(false),
ConstraintSet::from(false)
}
} }
} }