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May 28, 2025
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[ty] Synthetic function-like callables #18242

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8acdc14
[ty] Synthetic function-like callables
sharkdp May 21, 2025
dc83137
Add description of shortcut
sharkdp May 21, 2025
3adc8bd
Fall back to FunctionType
sharkdp May 21, 2025
7ab98df
Add tests for assignability/subtyping
sharkdp May 21, 2025
c4f93df
Add TODO
sharkdp May 21, 2025
eaab5d1
Handle function-like callables in subtyping, assignability
sharkdp May 23, 2025
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85 changes: 65 additions & 20 deletions crates/ty_python_semantic/resources/mdtest/dataclasses.md
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Original file line number Diff line number Diff line change
Expand Up @@ -56,8 +56,6 @@ Person(20, "Eve")

## Signature of `__init__`

TODO: All of the following tests are missing the `self` argument in the `__init__` signature.

Declarations in the class body are used to generate the signature of the `__init__` method. If the
attributes are not just declarations, but also bindings, the type inferred from bindings is used as
the default value.
Expand All @@ -71,7 +69,7 @@ class D:
y: str = "default"
z: int | None = 1 + 2

reveal_type(D.__init__) # revealed: (x: int, y: str = Literal["default"], z: int | None = Literal[3]) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int, y: str = Literal["default"], z: int | None = Literal[3]) -> None
```

This also works if the declaration and binding are split:
Expand All @@ -82,7 +80,7 @@ class D:
x: int | None
x = None

reveal_type(D.__init__) # revealed: (x: int | None = None) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int | None = None) -> None
```

Non-fully static types are handled correctly:
Expand All @@ -96,7 +94,7 @@ class C:
y: int | Any
z: tuple[int, Any]

reveal_type(C.__init__) # revealed: (x: Any, y: int | Any, z: tuple[int, Any]) -> None
reveal_type(C.__init__) # revealed: (self: C, x: Any, y: int | Any, z: tuple[int, Any]) -> None
```

Variables without annotations are ignored:
Expand All @@ -107,7 +105,7 @@ class D:
x: int
y = 1

reveal_type(D.__init__) # revealed: (x: int) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int) -> None
```

If attributes without default values are declared after attributes with default values, a
Expand All @@ -132,7 +130,7 @@ class D:
y: ClassVar[str] = "default"
z: bool

reveal_type(D.__init__) # revealed: (x: int, z: bool) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int, z: bool) -> None

d = D(1, True)
reveal_type(d.x) # revealed: int
Expand All @@ -150,7 +148,7 @@ class D:
def y(self) -> str:
return ""

reveal_type(D.__init__) # revealed: (x: int) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int) -> None
```

And neither do nested class declarations:
Expand All @@ -163,7 +161,7 @@ class D:
class Nested:
y: str

reveal_type(D.__init__) # revealed: (x: int) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int) -> None
```

But if there is a variable annotation with a function or class literal type, the signature of
Expand All @@ -181,7 +179,7 @@ class D:
class_literal: TypeOf[SomeClass]
class_subtype_of: type[SomeClass]

# revealed: (function_literal: def some_function() -> None, class_literal: <class 'SomeClass'>, class_subtype_of: type[SomeClass]) -> None
# revealed: (self: D, function_literal: def some_function() -> None, class_literal: <class 'SomeClass'>, class_subtype_of: type[SomeClass]) -> None
reveal_type(D.__init__)
```

Expand All @@ -194,7 +192,7 @@ from typing import Callable
class D:
c: Callable[[int], str]

reveal_type(D.__init__) # revealed: (c: (int, /) -> str) -> None
reveal_type(D.__init__) # revealed: (self: D, c: (int, /) -> str) -> None
```

Implicit instance attributes do not affect the signature of `__init__`:
Expand All @@ -209,7 +207,7 @@ class D:

reveal_type(D(1).y) # revealed: str

reveal_type(D.__init__) # revealed: (x: int) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int) -> None
```

Annotating expressions does not lead to an entry in `__annotations__` at runtime, and so it wouldn't
Expand All @@ -222,7 +220,7 @@ class D:
(x): int = 1

# TODO: should ideally not include a `x` parameter
reveal_type(D.__init__) # revealed: (x: int = Literal[1]) -> None
reveal_type(D.__init__) # revealed: (self: D, x: int = Literal[1]) -> None
```

## `@dataclass` calls with arguments
Expand Down Expand Up @@ -529,7 +527,7 @@ class C(Base):
z: int = 10
x: int = 15

reveal_type(C.__init__) # revealed: (x: int = Literal[15], y: int = Literal[0], z: int = Literal[10]) -> None
reveal_type(C.__init__) # revealed: (self: C, x: int = Literal[15], y: int = Literal[0], z: int = Literal[10]) -> None
```

## Generic dataclasses
Expand Down Expand Up @@ -582,7 +580,7 @@ class UppercaseString:
class C:
upper: UppercaseString = UppercaseString()

reveal_type(C.__init__) # revealed: (upper: str = str) -> None
reveal_type(C.__init__) # revealed: (self: C, upper: str = str) -> None

c = C("abc")
reveal_type(c.upper) # revealed: str
Expand Down Expand Up @@ -628,7 +626,7 @@ class ConvertToLength:
class C:
converter: ConvertToLength = ConvertToLength()

reveal_type(C.__init__) # revealed: (converter: str = Literal[""]) -> None
reveal_type(C.__init__) # revealed: (self: C, converter: str = Literal[""]) -> None

c = C("abc")
reveal_type(c.converter) # revealed: int
Expand Down Expand Up @@ -667,7 +665,7 @@ class AcceptsStrAndInt:
class C:
field: AcceptsStrAndInt = AcceptsStrAndInt()

reveal_type(C.__init__) # revealed: (field: str | int = int) -> None
reveal_type(C.__init__) # revealed: (self: C, field: str | int = int) -> None
```

## `dataclasses.field`
Expand Down Expand Up @@ -728,7 +726,7 @@ import dataclasses
class C:
x: str

reveal_type(C.__init__) # revealed: (x: str) -> None
reveal_type(C.__init__) # revealed: (self: C, x: str) -> None
```

### Dataclass with custom `__init__` method
Expand Down Expand Up @@ -821,10 +819,57 @@ reveal_type(Person.__mro__) # revealed: tuple[<class 'Person'>, <class 'object'
The generated methods have the following signatures:

```py
# TODO: `self` is missing here
reveal_type(Person.__init__) # revealed: (name: str, age: int | None = None) -> None
reveal_type(Person.__init__) # revealed: (self: Person, name: str, age: int | None = None) -> None

reveal_type(Person.__repr__) # revealed: def __repr__(self) -> str

reveal_type(Person.__eq__) # revealed: def __eq__(self, value: object, /) -> bool
```

## Function-like behavior of synthesized methods

Here, we make sure that the synthesized methods of dataclasses behave like proper functions.

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

```py
from dataclasses import dataclass
from typing import Callable
from types import FunctionType
from ty_extensions import CallableTypeOf, TypeOf, static_assert, is_subtype_of, is_assignable_to

@dataclass
class C:
x: int

reveal_type(C.__init__) # revealed: (self: C, x: int) -> None
reveal_type(type(C.__init__)) # revealed: <class 'FunctionType'>

# We can access attributes that are defined on functions:
reveal_type(type(C.__init__).__code__) # revealed: CodeType
reveal_type(C.__init__.__code__) # revealed: CodeType

def equivalent_signature(self: C, x: int) -> None:
pass

type DunderInitType = TypeOf[C.__init__]
type EquivalentPureCallableType = Callable[[C, int], None]
type EquivalentFunctionLikeCallableType = CallableTypeOf[equivalent_signature]

static_assert(is_subtype_of(DunderInitType, EquivalentPureCallableType))
static_assert(is_assignable_to(DunderInitType, EquivalentPureCallableType))

static_assert(not is_subtype_of(EquivalentPureCallableType, DunderInitType))
static_assert(not is_assignable_to(EquivalentPureCallableType, DunderInitType))

static_assert(is_subtype_of(DunderInitType, EquivalentFunctionLikeCallableType))
static_assert(is_assignable_to(DunderInitType, EquivalentFunctionLikeCallableType))

static_assert(not is_subtype_of(EquivalentFunctionLikeCallableType, DunderInitType))
static_assert(not is_assignable_to(EquivalentFunctionLikeCallableType, DunderInitType))

static_assert(is_subtype_of(DunderInitType, FunctionType))
```
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