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fix Django: Instance vs Class access of attributes should return different types #4080 #4336

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fix Django: Instance vs Class access of attributes should return different types #4080 #4336

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a93c815
test
asukaminato0721 Oct 30, 2026
53244dc
fix
asukaminato0721 Jul 27, 2026
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193 changes: 163 additions & 30 deletions pyrefly/lib/alt/class/class_field.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -262,6 +262,9 @@ pub struct Descriptor {
setter: bool,
/// Does `__delete__` exist on the descriptor?
deleter: bool,
/// Framework-provided getter and setter types for instance access.
/// Class access still calls the descriptor's `__get__`.
instance_types: Option<(Type, Type)>,
/// How the descriptor field was initialized. Used to distinguish class-body
/// descriptors (which have an actual object on the class) from annotation-only
/// descriptors (which rely on metaclass or other runtime machinery).
Expand Down Expand Up @@ -363,6 +366,8 @@ enum ClassFieldInner {
ty: Type,
annotation: Option<Annotation>,
descriptor: Descriptor,
is_foreign_key: bool,
has_choices: bool,
},
/// Methods (including abstract methods, functions without return annotations). We always
/// treat them as read only.
Expand Down Expand Up @@ -644,16 +649,24 @@ impl ClassField {
ty,
annotation,
descriptor,
is_foreign_key,
has_choices,
} => {
let mut ty = ty.clone();
f(&mut ty);
let mut descriptor = descriptor.clone();
descriptor.cls.visit_mut(f);
if let Some((getter, setter)) = &mut descriptor.instance_types {
f(getter);
f(setter);
}
Self(
ClassFieldInner::Descriptor {
ty,
annotation: annotation.clone(),
descriptor,
is_foreign_key: *is_foreign_key,
has_choices: *has_choices,
},
self.1.clone(),
)
Expand Down Expand Up @@ -844,9 +857,8 @@ impl ClassField {
| ClassFieldInner::NestedClass { .. }
| ClassFieldInner::ClassAttribute { .. } => false,
ClassFieldInner::Method { is_classvar, .. } => !is_classvar,
ClassFieldInner::Property { .. }
| ClassFieldInner::Descriptor { .. }
| ClassFieldInner::ProxyMethod { .. } => true,
ClassFieldInner::Descriptor { descriptor, .. } => descriptor.instance_types.is_none(),
ClassFieldInner::Property { .. } | ClassFieldInner::ProxyMethod { .. } => true,
}
}

Expand Down Expand Up @@ -906,7 +918,7 @@ impl ClassField {
pub fn is_foreign_key(&self) -> bool {
match &self.0 {
ClassFieldInner::Property { .. } => false,
ClassFieldInner::Descriptor { .. } => false,
ClassFieldInner::Descriptor { is_foreign_key, .. } => *is_foreign_key,
ClassFieldInner::Method { .. } => false,
ClassFieldInner::ProxyMethod { .. } => false,
ClassFieldInner::NestedClass { .. } => false,
Expand All @@ -918,7 +930,7 @@ impl ClassField {
pub fn has_choices(&self) -> bool {
match &self.0 {
ClassFieldInner::Property { .. } => false,
ClassFieldInner::Descriptor { .. } => false,
ClassFieldInner::Descriptor { has_choices, .. } => *has_choices,
ClassFieldInner::Method { .. } => false,
ClassFieldInner::ProxyMethod { .. } => false,
ClassFieldInner::NestedClass { .. } => false,
Expand Down Expand Up @@ -2278,7 +2290,7 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {

// Identify whether this is a descriptor. Construct the stored descriptor only after
// forcing the field type so its class cannot retain solver variables.
let mut descriptor_methods = None;
let mut descriptor_info = None;
let mut descriptor_range = None;
let is_annotation_initialized_in_method = match field_definition {
ClassFieldDefinition::DeclaredByAnnotation {
Expand Down Expand Up @@ -2310,7 +2322,8 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
|| has_deleter
|| has_getter && !is_annotation_initialized_in_method
{
descriptor_methods = Some((has_getter, has_setter, has_deleter));
descriptor_info =
Some(((has_getter, has_setter, has_deleter), ty.clone()));
}
}
// Only members with `__get__` participate in descriptor reads. A member with only
Expand Down Expand Up @@ -2343,23 +2356,41 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
false
};

let mut is_django_descriptor = false;
let ty = if let Some(special_ty) = self.get_special_class_field_type(
class,
name,
direct_annotation.as_ref(),
&ty,
unpromoted_ty.as_ref(),
field_definition,
descriptor_methods.is_some() || descriptor_range.is_some(),
descriptor_info.is_some() || descriptor_range.is_some(),
range,
errors,
) {
// Don't use the descriptor, since we've set a custom type instead.
descriptor_methods = None;
descriptor_info = None;
descriptor_range = None;
special_ty
} else {
ty
let initial_value_expr = match field_definition {
ClassFieldDefinition::AssignedInBody { value, .. } => {
if let ExprOrBinding::Expr(expr) = value.as_ref() {
Some(expr)
} else {
None
}
}
_ => None,
};
if let Some(django_ty) =
self.get_django_field_type(&ty, class, Some(name), initial_value_expr)
{
is_django_descriptor = descriptor_info.is_some();
django_ty
} else {
ty
}
};

// Pin any vars in the type: leaking a var in a class field is particularly
Expand All @@ -2368,18 +2399,27 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
// TODO(stroxler): Ideally we would implement some simple heuristics, similar to
// first-use based inference we use with assignments, to get more useful types here.
let ty = self.solver().force(ty);
let descriptor = match (descriptor_methods, &ty) {
(Some((getter, setter, deleter)), Type::ClassType(cls)) => Some(Descriptor {
let descriptor = descriptor_info.map(|((getter, setter, deleter), descriptor_type)| {
let Type::ClassType(mut cls) = self.solver().force(descriptor_type) else {
unreachable!("a detected descriptor must have a class type")
};
let instance_types = is_django_descriptor.then(|| {
let (field_type, set_type) =
self.specialize_django_field_descriptor(&cls, ty.clone());
cls = field_type;
(ty.clone(), set_type)
});
Descriptor {
range,
cls: cls.clone(),
cls,
getter,
setter,
deleter,
instance_types,
initialization: initialization.clone(),
is_override: descriptor_is_override,
}),
_ => None,
};
}
});

let direct_annotation_idx = match field_definition {
ClassFieldDefinition::DeclaredByAnnotation { annotation, .. } => Some(*annotation),
Expand Down Expand Up @@ -2512,6 +2552,8 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
ty,
annotation,
descriptor,
is_foreign_key,
has_choices,
},
is_inherited,
)
Expand Down Expand Up @@ -2761,19 +2803,6 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
)
.or_else(|| self.get_property_class_field_type(class, name, field_definition))
.or_else(|| self.get_pydantic_root_model_class_field_type(class, name))
.or_else(|| {
let initial_value_expr = match field_definition {
ClassFieldDefinition::AssignedInBody { value, .. } => {
if let ExprOrBinding::Expr(expr) = value.as_ref() {
Some(expr)
} else {
None
}
}
_ => None,
};
self.get_django_field_type(ty, class, Some(name), initial_value_expr)
})
}

/// Recognize `x = property(fget, fset, fdel)` and return the corresponding
Expand Down Expand Up @@ -3274,6 +3303,25 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
} else {
IsInherited::Maybe
};
if !inferred_from_method
&& inherited_annotation.is_some()
&& self.get_metadata_for_class(class).is_django_model()
&& let ExprOrBinding::Expr(expr) = value
{
let field_ty = self.attribute_expr_infer(expr, None, name, &self.error_swallower());
if self
.get_django_field_type(&field_ty, class, Some(name), Some(expr))
.is_some()
{
// Django installs a descriptor, whose instance contract is checked by the
// override check. The inherited value annotation cannot type its initializer.
return (
self.attribute_expr_infer(expr, None, name, errors),
None,
is_inherited,
);
}
}
let final_annotation = Self::merge_direct_qualifiers_with_inherited_annotation(
inherited_annotation.clone(),
direct_qualifiers,
Expand Down Expand Up @@ -5710,6 +5758,14 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
Some(AttrSetter::PropertySetter(setter))
}
ClassAttribute::Descriptor(x, base) => match base {
DescriptorBase::Instance(_) | DescriptorBase::SelfInstance(_)
if let Some((_, set_type)) = &x.instance_types =>
{
Some(AttrSetter::Declared {
ty: set_type.clone(),
narrow: false,
})
}
DescriptorBase::Instance(_) | DescriptorBase::SelfInstance(_)
if let Some(setter) = self.resolve_descriptor_setter(attr_name, &x, errors) =>
{
Expand Down Expand Up @@ -6083,13 +6139,76 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
(_, None) => Ok(()),
}
}
(
ClassAttribute::Descriptor(desc, base),
ClassAttribute::ReadWrite(want_ty, _) | ClassAttribute::ReadOnly(want_ty, _),
) if desc.instance_types.is_some() => {
let (read_ty, setter) = self.resolve_descriptor_types(desc, base);
is_subset(&read_ty, want_ty).map_err(|subset_error| {
Box::new(AttrSubsetError::Covariant {
got: read_ty.clone(),
want: want_ty.clone(),
got_is_property: false,
want_is_property: false,
subset_error,
})
})?;
if matches!(want, ClassAttribute::ReadWrite(..)) {
let Some(set_ty) = setter else {
return Err(Box::new(AttrSubsetError::ReadOnly));
};
is_subset(want_ty, &set_ty).map_err(|subset_error| {
Box::new(AttrSubsetError::Contravariant {
got: set_ty,
want: want_ty.clone(),
got_is_property: false,
want_is_property: false,
subset_error,
})
})?;
}
Ok(())
}
(
ClassAttribute::ReadWrite(got_ty, _) | ClassAttribute::ReadOnly(got_ty, _),
ClassAttribute::Descriptor(desc, base),
) if desc.instance_types.is_some() => {
let (read_ty, setter) = self.resolve_descriptor_types(desc, base);
is_subset(got_ty, &read_ty).map_err(|subset_error| {
Box::new(AttrSubsetError::Covariant {
got: got_ty.clone(),
want: read_ty.clone(),
got_is_property: false,
want_is_property: false,
subset_error,
})
})?;
if let Some(set_ty) = setter {
if matches!(got, ClassAttribute::ReadOnly(..)) {
return Err(Box::new(AttrSubsetError::ReadOnly));
}
is_subset(&set_ty, got_ty).map_err(|subset_error| {
Box::new(AttrSubsetError::Contravariant {
got: got_ty.clone(),
want: set_ty,
got_is_property: false,
want_is_property: false,
subset_error,
})
})?;
}
Ok(())
}
(
ClassAttribute::Descriptor(got_d, got_base),
ClassAttribute::Descriptor(want_d, want_base),
) => {
let got_ty = self.heap.mk_class_type(got_d.cls.clone());
let want_ty = self.heap.mk_class_type(want_d.cls.clone());
if is_subset(&got_ty, &want_ty).is_ok() {
if got_d.instance_types.is_none()
&& want_d.instance_types.is_none()
&& is_subset(&got_ty, &want_ty).is_ok()
{
return Ok(());
}
let (got_read_ty, got_setter) = self.resolve_descriptor_types(got_d, got_base);
Expand Down Expand Up @@ -6264,6 +6383,13 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
Ok(self.call_property_getter(getter, range, errors, context))
}
ClassAttribute::Descriptor(x, base) => {
if matches!(
&base,
DescriptorBase::Instance(_) | DescriptorBase::SelfInstance(_)
) && let Some((get_type, _)) = &x.instance_types
{
return Ok(get_type.clone());
}
if let Some(getter) = self.resolve_descriptor_getter(attr_name, &x, errors) {
// Reading a descriptor with a getter resolves to a method call
//
Expand Down Expand Up @@ -6310,6 +6436,13 @@ impl<'ctx, 'answer, Ans: LookupAnswer> AnswersSolver<'ctx, 'answer, Ans> {
desc: &Descriptor,
base: &DescriptorBase,
) -> (Type, Option<Type>) {
if matches!(
base,
DescriptorBase::Instance(_) | DescriptorBase::SelfInstance(_)
) && let Some((getter, setter)) = &desc.instance_types
{
return (getter.clone(), desc.setter.then(|| setter.clone()));
}
let error_swallower = self.error_swallower();
let read_ty = if let Some(getter) =
self.resolve_descriptor_getter(&dunder::GET, desc, &error_swallower)
Expand Down
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