Skip to content

[ty] Support frozen dataclasses #17974

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 4 commits into from
May 22, 2025
Merged

[ty] Support frozen dataclasses #17974

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
dcf210d
[ty] Support frozen dataclasses
thejchap May 6, 2025
c9d1aaf
Apply suggestions from code review
thejchap May 9, 2025
c38ec21
[ty] Refactor frozen dataclass diagnostic
thejchap May 9, 2025
c9ca199
a few adjustments
carljm May 22, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
60 changes: 59 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/dataclasses.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -369,7 +369,65 @@ To do

### `frozen`

To do
If true (the default is False), assigning to fields will generate a diagnostic.

```py
from dataclasses import dataclass

@dataclass(frozen=True)
class MyFrozenClass:
x: int

frozen_instance = MyFrozenClass(1)
frozen_instance.x = 2 # error: [invalid-assignment]
```

If `__setattr__()` or `__delattr__()` is defined in the class, we should emit a diagnostic.

```py
from dataclasses import dataclass

@dataclass(frozen=True)
class MyFrozenClass:
x: int

# TODO: Emit a diagnostic here
def __setattr__(self, name: str, value: object) -> None: ...

# TODO: Emit a diagnostic here
def __delattr__(self, name: str) -> None: ...
```

This also works for generic dataclasses:

```toml
[environment]
python-version = "3.12"
```

```py
from dataclasses import dataclass

@dataclass(frozen=True)
class MyFrozenGeneric[T]:
x: T

frozen_instance = MyFrozenGeneric[int](1)
frozen_instance.x = 2 # error: [invalid-assignment]
```

When attempting to mutate an unresolved attribute on a frozen dataclass, only `unresolved-attribute`
is emitted:

```py
from dataclasses import dataclass

@dataclass(frozen=True)
class MyFrozenClass: ...

frozen = MyFrozenClass()
frozen.x = 2 # error: [unresolved-attribute]
```

### `match_args`

Expand Down
143 changes: 93 additions & 50 deletions crates/ty_python_semantic/src/types/infer.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3088,6 +3088,20 @@ impl<'db> TypeInferenceBuilder<'db> {
| Type::TypeVar(..)
| Type::AlwaysTruthy
| Type::AlwaysFalsy => {
let is_read_only = || {
let dataclass_params = match object_ty {
Type::NominalInstance(instance) => match instance.class {
ClassType::NonGeneric(cls) => cls.dataclass_params(self.db()),
ClassType::Generic(cls) => {
cls.origin(self.db()).dataclass_params(self.db())
}
},
_ => None,
};

dataclass_params.is_some_and(|params| params.contains(DataclassParams::FROZEN))
};

match object_ty.class_member(db, attribute.into()) {
meta_attr @ SymbolAndQualifiers { .. } if meta_attr.is_class_var() => {
if emit_diagnostics {
Expand All @@ -3107,68 +3121,83 @@ impl<'db> TypeInferenceBuilder<'db> {
symbol: Symbol::Type(meta_attr_ty, meta_attr_boundness),
qualifiers: _,
} => {
let assignable_to_meta_attr = if let Symbol::Type(meta_dunder_set, _) =
meta_attr_ty.class_member(db, "__set__".into()).symbol
{
let successful_call = meta_dunder_set
.try_call(
db,
&CallArgumentTypes::positional([
meta_attr_ty,
object_ty,
value_ty,
]),
)
.is_ok();

if !successful_call && emit_diagnostics {
if is_read_only() {
if emit_diagnostics {
if let Some(builder) =
self.context.report_lint(&INVALID_ASSIGNMENT, target)
{
// TODO: Here, it would be nice to emit an additional diagnostic that explains why the call failed
builder.into_diagnostic(format_args!(
"Invalid assignment to data descriptor attribute \
`{attribute}` on type `{}` with custom `__set__` method",
object_ty.display(db)
"Property `{attribute}` defined in `{ty}` is read-only",
ty = object_ty.display(self.db()),
));
}
}

successful_call
false
} else {
ensure_assignable_to(meta_attr_ty)
};
let assignable_to_meta_attr = if let Symbol::Type(meta_dunder_set, _) =
meta_attr_ty.class_member(db, "__set__".into()).symbol
{
let successful_call = meta_dunder_set
.try_call(
db,
&CallArgumentTypes::positional([
meta_attr_ty,
object_ty,
value_ty,
]),
)
.is_ok();

let assignable_to_instance_attribute = if meta_attr_boundness
== Boundness::PossiblyUnbound
{
let (assignable, boundness) =
if let Symbol::Type(instance_attr_ty, instance_attr_boundness) =
object_ty.instance_member(db, attribute).symbol
{
(
ensure_assignable_to(instance_attr_ty),
if !successful_call && emit_diagnostics {
if let Some(builder) =
self.context.report_lint(&INVALID_ASSIGNMENT, target)
{
// TODO: Here, it would be nice to emit an additional diagnostic that explains why the call failed
builder.into_diagnostic(format_args!(
"Invalid assignment to data descriptor attribute \
`{attribute}` on type `{}` with custom `__set__` method",
object_ty.display(db)
));
}
}

successful_call
} else {
ensure_assignable_to(meta_attr_ty)
};

let assignable_to_instance_attribute =
if meta_attr_boundness == Boundness::PossiblyUnbound {
let (assignable, boundness) = if let Symbol::Type(
instance_attr_ty,
instance_attr_boundness,
)
} else {
(true, Boundness::PossiblyUnbound)
};
) =
object_ty.instance_member(db, attribute).symbol
{
(
ensure_assignable_to(instance_attr_ty),
instance_attr_boundness,
)
} else {
(true, Boundness::PossiblyUnbound)
};

if boundness == Boundness::PossiblyUnbound {
report_possibly_unbound_attribute(
&self.context,
target,
attribute,
object_ty,
);
}
if boundness == Boundness::PossiblyUnbound {
report_possibly_unbound_attribute(
&self.context,
target,
attribute,
object_ty,
);
}

assignable
} else {
true
};
assignable
} else {
true
};

assignable_to_meta_attr && assignable_to_instance_attribute
assignable_to_meta_attr && assignable_to_instance_attribute
}
}

SymbolAndQualifiers {
Expand All @@ -3187,7 +3216,21 @@ impl<'db> TypeInferenceBuilder<'db> {
);
}

ensure_assignable_to(instance_attr_ty)
if is_read_only() {
if emit_diagnostics {
if let Some(builder) =
self.context.report_lint(&INVALID_ASSIGNMENT, target)
{
builder.into_diagnostic(format_args!(
"Property `{attribute}` defined in `{ty}` is read-only",
ty = object_ty.display(self.db()),
));
}
}
false
} else {
ensure_assignable_to(instance_attr_ty)
}
} else {
let result = object_ty.try_call_dunder_with_policy(
db,
Expand Down
Loading