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Infer list[T] for starred target in unpacking #18401

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Merged
merged 1 commit into from
Jun 3, 2025
Merged

Infer list[T] for starred target in unpacking #18401

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2 changes: 1 addition & 1 deletion crates/ty_python_semantic/resources/mdtest/attributes.md
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Original file line number Diff line number Diff line change
Expand Up @@ -302,7 +302,7 @@ class C:

c_instance = C()
reveal_type(c_instance.a) # revealed: Unknown | Literal[1]
reveal_type(c_instance.b) # revealed: Unknown
reveal_type(c_instance.b) # revealed: Unknown | list[Literal[2, 3]]
```

#### Attributes defined in for-loop (unpacking)
Expand Down
40 changes: 14 additions & 26 deletions crates/ty_python_semantic/resources/mdtest/unpacking.md
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Original file line number Diff line number Diff line change
Expand Up @@ -109,8 +109,7 @@ reveal_type(d) # revealed: Literal[5]
# error: [invalid-assignment] "Not enough values to unpack: Expected 3 or more"
[a, *b, c, d] = (1, 2)
reveal_type(a) # revealed: Unknown
# TODO: Should be list[Any] once support for assigning to starred expression is added
reveal_type(b) # revealed: Unknown
reveal_type(b) # revealed: list[Unknown]
reveal_type(c) # revealed: Unknown
reveal_type(d) # revealed: Unknown
```
Expand All @@ -120,8 +119,7 @@ reveal_type(d) # revealed: Unknown
```py
[a, *b, c] = (1, 2)
reveal_type(a) # revealed: Literal[1]
# TODO: Should be list[Any] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[Unknown]
reveal_type(c) # revealed: Literal[2]
```

Expand All @@ -130,8 +128,7 @@ reveal_type(c) # revealed: Literal[2]
```py
[a, *b, c] = (1, 2, 3)
reveal_type(a) # revealed: Literal[1]
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[Literal[2]]
reveal_type(c) # revealed: Literal[3]
```

Expand All @@ -140,8 +137,7 @@ reveal_type(c) # revealed: Literal[3]
```py
[a, *b, c, d] = (1, 2, 3, 4, 5, 6)
reveal_type(a) # revealed: Literal[1]
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[Literal[2, 3, 4]]
reveal_type(c) # revealed: Literal[5]
reveal_type(d) # revealed: Literal[6]
```
Expand All @@ -152,8 +148,7 @@ reveal_type(d) # revealed: Literal[6]
[a, b, *c] = (1, 2, 3, 4)
reveal_type(a) # revealed: Literal[1]
reveal_type(b) # revealed: Literal[2]
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(c) # revealed: @Todo(starred unpacking)
reveal_type(c) # revealed: list[Literal[3, 4]]
```

### Starred expression (6)
Expand All @@ -164,7 +159,7 @@ reveal_type(c) # revealed: @Todo(starred unpacking)
reveal_type(a) # revealed: Unknown
reveal_type(b) # revealed: Unknown
reveal_type(c) # revealed: Unknown
reveal_type(d) # revealed: Unknown
reveal_type(d) # revealed: list[Unknown]
reveal_type(e) # revealed: Unknown
reveal_type(f) # revealed: Unknown
```
Expand Down Expand Up @@ -247,8 +242,7 @@ reveal_type(b) # revealed: Unknown
# error: [invalid-assignment] "Not enough values to unpack: Expected 3 or more"
(a, *b, c, d) = "ab"
reveal_type(a) # revealed: Unknown
# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
reveal_type(b) # revealed: Unknown
reveal_type(b) # revealed: list[Unknown]
reveal_type(c) # revealed: Unknown
reveal_type(d) # revealed: Unknown
```
Expand All @@ -258,7 +252,7 @@ reveal_type(d) # revealed: Unknown
(a, b, *c, d) = "a"
reveal_type(a) # revealed: Unknown
reveal_type(b) # revealed: Unknown
reveal_type(c) # revealed: Unknown
reveal_type(c) # revealed: list[Unknown]
reveal_type(d) # revealed: Unknown
```

Expand All @@ -267,8 +261,7 @@ reveal_type(d) # revealed: Unknown
```py
(a, *b, c) = "ab"
reveal_type(a) # revealed: LiteralString
# TODO: Should be list[Any] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[Unknown]
reveal_type(c) # revealed: LiteralString
```

Expand All @@ -277,8 +270,7 @@ reveal_type(c) # revealed: LiteralString
```py
(a, *b, c) = "abc"
reveal_type(a) # revealed: LiteralString
# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[LiteralString]
reveal_type(c) # revealed: LiteralString
```

Expand All @@ -287,8 +279,7 @@ reveal_type(c) # revealed: LiteralString
```py
(a, *b, c, d) = "abcdef"
reveal_type(a) # revealed: LiteralString
# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[LiteralString]
reveal_type(c) # revealed: LiteralString
reveal_type(d) # revealed: LiteralString
```
Expand All @@ -299,8 +290,7 @@ reveal_type(d) # revealed: LiteralString
(a, b, *c) = "abcd"
reveal_type(a) # revealed: LiteralString
reveal_type(b) # revealed: LiteralString
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(c) # revealed: @Todo(starred unpacking)
reveal_type(c) # revealed: list[LiteralString]
```

### Unicode
Expand Down Expand Up @@ -411,8 +401,7 @@ def _(arg: tuple[int, tuple[str, bytes]] | tuple[tuple[int, bytes], Literal["ab"
def _(arg: tuple[int, bytes, int] | tuple[int, int, str, int, bytes]):
a, *b, c = arg
reveal_type(a) # revealed: int
# TODO: Should be `list[bytes | int | str]`
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[bytes] | list[int | str]
reveal_type(c) # revealed: int | bytes
```

Expand Down Expand Up @@ -676,8 +665,7 @@ class ContextManager:

with ContextManager() as (a, *b):
reveal_type(a) # revealed: int
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo(starred unpacking)
reveal_type(b) # revealed: list[int]
```

### Unbound context manager expression
Expand Down
32 changes: 24 additions & 8 deletions crates/ty_python_semantic/src/types/unpacker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,12 +8,12 @@ use ruff_python_ast::{self as ast, AnyNodeRef};
use crate::Db;
use crate::semantic_index::ast_ids::{HasScopedExpressionId, ScopedExpressionId};
use crate::semantic_index::symbol::ScopeId;
use crate::types::{Type, TypeCheckDiagnostics, infer_expression_types, todo_type};
use crate::types::{Type, TypeCheckDiagnostics, infer_expression_types};
use crate::unpack::{UnpackKind, UnpackValue};

use super::context::InferContext;
use super::diagnostic::INVALID_ASSIGNMENT;
use super::{TupleType, UnionType};
use super::{KnownClass, TupleType, UnionType};

/// Unpacks the value expression type to their respective targets.
pub(crate) struct Unpacker<'db> {
Expand Down Expand Up @@ -253,12 +253,17 @@ impl<'db> Unpacker<'db> {
let starred_end_index = tuple_ty.len(self.db()) - remaining;

// SAFETY: Safe because of the length check above.
let _starred_element_types =
let starred_element_types =
&tuple_ty.elements(self.db())[starred_index..starred_end_index];
// TODO: Combine the types into a list type. If the
// starred_element_types is empty, then it should be `List[Any]`.
// combine_types(starred_element_types);
element_types.push(todo_type!("starred unpacking"));

element_types.push(KnownClass::List.to_specialized_instance(
self.db(),
[if starred_element_types.is_empty() {
Type::unknown()
} else {
UnionType::from_elements(self.db(), starred_element_types)
}],
));

// Insert the types remaining that aren't consumed by the starred expression.
element_types.extend_from_slice(
Expand All @@ -278,7 +283,18 @@ impl<'db> Unpacker<'db> {
);
}

Cow::Owned(vec![Type::unknown(); targets.len()])
Cow::Owned(
targets
.iter()
.map(|target| {
if target.is_starred_expr() {
KnownClass::List.to_specialized_instance(self.db(), [Type::unknown()])
} else {
Type::unknown()
}
})
.collect(),
)
}
}

Expand Down
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