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Merged
merged 3 commits into from
Nov 18, 2025
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[ty] tighten up handling of subscripts in type expressions #21503

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7e3ed18
[ty] tighten up handling of subscripts in type expressions
carljm Nov 17, 2025
d32b0d6
review feedback
carljm Nov 18, 2025
d58fb4d
more diagnostics in attrs
carljm Nov 18, 2025
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2 changes: 1 addition & 1 deletion crates/ruff_benchmark/benches/ty.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -667,7 +667,7 @@ fn attrs(criterion: &mut Criterion) {
max_dep_date: "2025-06-17",
python_version: PythonVersion::PY313,
},
110,
120,
);

bench_project(&benchmark, criterion);
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6 changes: 4 additions & 2 deletions crates/ty_python_semantic/resources/mdtest/annotations/invalid.md
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Expand Up @@ -98,7 +98,9 @@ async def outer_async(): # avoid unrelated syntax errors on `yield` and `await`
n: 1 < 2, # error: [invalid-type-form] "Comparison expressions are not allowed in type expressions"
o: bar(), # error: [invalid-type-form] "Function calls are not allowed in type expressions"
p: int | f"foo", # error: [invalid-type-form] "F-strings are not allowed in type expressions"
q: [1, 2, 3][1:2], # error: [invalid-type-form] "Slices are not allowed in type expressions"
# error: [invalid-type-form] "Slices are not allowed in type expressions"
# error: [invalid-type-form] "Invalid subscript"
q: [1, 2, 3][1:2],
):
reveal_type(a) # revealed: Unknown
reveal_type(b) # revealed: Unknown
Expand All @@ -116,7 +118,7 @@ async def outer_async(): # avoid unrelated syntax errors on `yield` and `await`
reveal_type(n) # revealed: Unknown
reveal_type(o) # revealed: Unknown
reveal_type(p) # revealed: int | Unknown
reveal_type(q) # revealed: @Todo(unknown type subscript)
reveal_type(q) # revealed: Unknown

class Mat:
def __init__(self, value: int):
Expand Down
3 changes: 2 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/annotations/literal.md
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Expand Up @@ -330,10 +330,11 @@ from other import Literal
# ?
#
# error: [invalid-type-form] "Int literals are not allowed in this context in a type expression"
# error: [invalid-type-form] "Invalid subscript of object of type `_SpecialForm` in type expression"
a1: Literal[26]

def f():
reveal_type(a1) # revealed: @Todo(unknown type subscript)
reveal_type(a1) # revealed: Unknown
```

## Detecting typing_extensions.Literal
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26 changes: 24 additions & 2 deletions crates/ty_python_semantic/resources/mdtest/implicit_type_aliases.md
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Expand Up @@ -33,9 +33,11 @@ g(None)
We also support unions in type aliases:

```py
from typing_extensions import Any, Never, Literal, LiteralString, Tuple, Annotated, Optional, Union, Callable
from typing_extensions import Any, Never, Literal, LiteralString, Tuple, Annotated, Optional, Union, Callable, TypeVar
from ty_extensions import Unknown

T = TypeVar("T")

IntOrStr = int | str
IntOrStrOrBytes1 = int | str | bytes
IntOrStrOrBytes2 = (int | str) | bytes
Expand Down Expand Up @@ -70,6 +72,10 @@ IntOrTypeOfStr = int | type[str]
TypeOfStrOrInt = type[str] | int
IntOrCallable = int | Callable[[str], bytes]
CallableOrInt = Callable[[str], bytes] | int
TypeVarOrInt = T | int
IntOrTypeVar = int | T
TypeVarOrNone = T | None
NoneOrTypeVar = None | T

reveal_type(IntOrStr) # revealed: types.UnionType
reveal_type(IntOrStrOrBytes1) # revealed: types.UnionType
Expand Down Expand Up @@ -105,6 +111,10 @@ reveal_type(IntOrTypeOfStr) # revealed: types.UnionType
reveal_type(TypeOfStrOrInt) # revealed: types.UnionType
reveal_type(IntOrCallable) # revealed: types.UnionType
reveal_type(CallableOrInt) # revealed: types.UnionType
reveal_type(TypeVarOrInt) # revealed: types.UnionType
reveal_type(IntOrTypeVar) # revealed: types.UnionType
reveal_type(TypeVarOrNone) # revealed: types.UnionType
reveal_type(NoneOrTypeVar) # revealed: types.UnionType

def _(
int_or_str: IntOrStr,
Expand Down Expand Up @@ -141,6 +151,10 @@ def _(
type_of_str_or_int: TypeOfStrOrInt,
int_or_callable: IntOrCallable,
callable_or_int: CallableOrInt,
type_var_or_int: TypeVarOrInt,
int_or_type_var: IntOrTypeVar,
type_var_or_none: TypeVarOrNone,
none_or_type_var: NoneOrTypeVar,
):
reveal_type(int_or_str) # revealed: int | str
reveal_type(int_or_str_or_bytes1) # revealed: int | str | bytes
Expand Down Expand Up @@ -176,6 +190,14 @@ def _(
reveal_type(type_of_str_or_int) # revealed: type[str] | int
reveal_type(int_or_callable) # revealed: int | ((str, /) -> bytes)
reveal_type(callable_or_int) # revealed: ((str, /) -> bytes) | int
# TODO should be Unknown | int
reveal_type(type_var_or_int) # revealed: T@_ | int
# TODO should be int | Unknown
reveal_type(int_or_type_var) # revealed: int | T@_
# TODO should be Unknown | None
reveal_type(type_var_or_none) # revealed: T@_ | None
# TODO should be None | Unknown
reveal_type(none_or_type_var) # revealed: None | T@_
Comment on lines +193 to +200
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@sharkdp sharkdp Nov 18, 2025

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Working on it ... 😄

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@carljm carljm Nov 18, 2025

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I was actually going to ask if you wanted these tests here or in a separate "generics" section, since they are testing the combination of both generic aliases and unions :) Feel free to move them if you want in your PR.

```

If a type is unioned with itself in a value expression, the result is just that type. No
Expand Down Expand Up @@ -357,7 +379,7 @@ MyList = list[T]

def _(my_list: MyList[int]):
# TODO: This should be `list[int]`
reveal_type(my_list) # revealed: @Todo(unknown type subscript)
reveal_type(my_list) # revealed: @Todo(specialized generic alias in type expression)

ListOrTuple = list[T] | tuple[T, ...]

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9 changes: 7 additions & 2 deletions crates/ty_python_semantic/src/types/infer/builder.rs
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Expand Up @@ -9507,7 +9507,8 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
| KnownInstanceType::Literal(_)
| KnownInstanceType::Annotated(_)
| KnownInstanceType::TypeGenericAlias(_)
| KnownInstanceType::Callable(_),
| KnownInstanceType::Callable(_)
| KnownInstanceType::TypeVar(_),
),
Type::ClassLiteral(..)
| Type::SubclassOf(..)
Expand All @@ -9518,7 +9519,8 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
| KnownInstanceType::Literal(_)
| KnownInstanceType::Annotated(_)
| KnownInstanceType::TypeGenericAlias(_)
| KnownInstanceType::Callable(_),
| KnownInstanceType::Callable(_)
| KnownInstanceType::TypeVar(_),
),
ast::Operator::BitOr,
) if pep_604_unions_allowed() => {
Expand Down Expand Up @@ -10926,6 +10928,9 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
.map(Type::from)
.unwrap_or_else(Type::unknown);
}
Type::KnownInstance(KnownInstanceType::UnionType(_)) => {
return todo_type!("Specialization of union type alias");
}
_ => {}
}

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24 changes: 20 additions & 4 deletions crates/ty_python_semantic/src/types/infer/builder/type_expression.rs
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Expand Up @@ -858,7 +858,7 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
Type::unknown()
}
},
Type::Dynamic(DynamicType::Todo(_)) => {
Type::Dynamic(_) => {
self.infer_type_expression(slice);
value_ty
}
Expand Down Expand Up @@ -887,11 +887,27 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
}
}
}
Type::GenericAlias(_) => {
self.infer_type_expression(slice);
// If the generic alias is already fully specialized, this is an error. But it
// could have been specialized with another typevar (e.g. a type alias like `MyList
// = list[T]`), in which case it's later valid to do `MyList[int]`.
todo_type!("specialized generic alias in type expression")
}
Type::StringLiteral(_) => {
self.infer_type_expression(slice);
// For stringified TypeAlias; remove once properly supported
todo_type!("string literal subscripted in type expression")
}
_ => {
// TODO: Emit a diagnostic once we've implemented all valid subscript type
// expressions.
self.infer_type_expression(slice);
todo_type!("unknown type subscript")
if let Some(builder) = self.context.report_lint(&INVALID_TYPE_FORM, subscript) {
builder.into_diagnostic(format_args!(
"Invalid subscript of object of type `{}` in type expression",
value_ty.display(self.db())
));
}
Type::unknown()
}
}
}
Expand Down