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Use Never instead of None for stores #13984

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merged 1 commit into from
Oct 30, 2024
Merged

Use Never instead of None for stores #13984

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28 changes: 10 additions & 18 deletions crates/red_knot_python_semantic/resources/mdtest/unpacking.md
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Original file line number Diff line number Diff line change
Expand Up @@ -81,8 +81,7 @@ reveal_type(b) # revealed: Literal[2]

```py
# TODO: Add diagnostic (need more values to unpack)
# TODO: Remove 'not-iterable' diagnostic
[a, *b, c, d] = (1, 2) # error: "Object of type `None` is not iterable"
[a, *b, c, d] = (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
Expand All @@ -93,7 +92,7 @@ reveal_type(d) # revealed: Unknown
### Starred expression (2)

```py
[a, *b, c] = (1, 2) # error: "Object of type `None` is not iterable"
[a, *b, c] = (1, 2)
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I'm having trouble tracing this -- where is this diagnostic even coming from today?

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What's the issue? Is this failing? I think that's probably coming from infer_starred_expression

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The diagnostic is no longer showing up, so I had to remove these assertions along with the TODOs to remove them (?).

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Yeah, I think that's correct. The diagnostics shouldn't be present in these cases and I think I left out one TODO in this specific case which might've confused you (?). The reason these diagnostics were showing up in the first place is because red knot tries to infer the starred expression (*b) but that isn't supported yet, before this PR it would've returned None and then it would raise a "not-an-iterable" diagnostic. But, it's now changed to use Never in this PR.

ruff/crates/red_knot_python_semantic/src/types/infer.rs

Lines 2341 to 2344 in c6b8215

let iterable_ty = self.infer_expression(value);
iterable_ty
.iterate(self.db)
.unwrap_with_diagnostic(value.as_ref().into(), self);

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This PR shouldn't even affect this case (we should never use the type of a Store-context expression), but it does just because we don't support assigning to Starred yet, and the way the temporary code works out, it does currently try to iterate the inferred type of a Store-context expression. But not throwing the error is better, so if anything switching from None to Never is an improvement here.

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
Expand All @@ -103,8 +102,7 @@ reveal_type(c) # revealed: Literal[2]
### Starred expression (3)

```py
# TODO: Remove 'not-iterable' diagnostic
[a, *b, c] = (1, 2, 3) # error: "Object of type `None` is not iterable"
[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
Expand All @@ -114,8 +112,7 @@ reveal_type(c) # revealed: Literal[3]
### Starred expression (4)

```py
# TODO: Remove 'not-iterable' diagnostic
[a, *b, c, d] = (1, 2, 3, 4, 5, 6) # error: "Object of type `None` is not iterable"
[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
Expand All @@ -126,8 +123,7 @@ reveal_type(d) # revealed: Literal[6]
### Starred expression (5)

```py
# TODO: Remove 'not-iterable' diagnostic
[a, b, *c] = (1, 2, 3, 4) # error: "Object of type `None` is not iterable"
[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
Expand Down Expand Up @@ -215,8 +211,7 @@ reveal_type(b) # revealed: LiteralString

```py
# TODO: Add diagnostic (need more values to unpack)
# TODO: Remove 'not-iterable' diagnostic
(a, *b, c, d) = "ab" # error: "Object of type `None` is not iterable"
(a, *b, c, d) = "ab"
reveal_type(a) # revealed: LiteralString
# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
reveal_type(b) # revealed: @Todo
Expand All @@ -227,7 +222,7 @@ reveal_type(d) # revealed: Unknown
### Starred expression (2)

```py
(a, *b, c) = "ab" # error: "Object of type `None` is not iterable"
(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
Expand All @@ -237,8 +232,7 @@ reveal_type(c) # revealed: LiteralString
### Starred expression (3)

```py
# TODO: Remove 'not-iterable' diagnostic
(a, *b, c) = "abc" # error: "Object of type `None` is not iterable"
(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
Expand All @@ -248,8 +242,7 @@ reveal_type(c) # revealed: LiteralString
### Starred expression (4)

```py
# TODO: Remove 'not-iterable' diagnostic
(a, *b, c, d) = "abcdef" # error: "Object of type `None` is not iterable"
(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
Expand All @@ -260,8 +253,7 @@ reveal_type(d) # revealed: LiteralString
### Starred expression (5)

```py
# TODO: Remove 'not-iterable' diagnostic
(a, b, *c) = "abcd" # error: "Object of type `None` is not iterable"
(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
Expand Down
8 changes: 4 additions & 4 deletions crates/red_knot_python_semantic/src/types/infer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1414,11 +1414,11 @@ impl<'db> TypeInferenceBuilder<'db> {
// Resolve the target type, assuming a load context.
let target_type = match &**target {
Expr::Name(name) => {
self.store_expression_type(target, Type::None);
self.store_expression_type(target, Type::Never);
self.infer_name_load(name)
}
Expr::Attribute(attr) => {
self.store_expression_type(target, Type::None);
self.store_expression_type(target, Type::Never);
self.infer_attribute_load(attr)
}
_ => self.infer_expression(target),
Expand Down Expand Up @@ -2501,7 +2501,7 @@ impl<'db> TypeInferenceBuilder<'db> {
fn infer_name_expression(&mut self, name: &ast::ExprName) -> Type<'db> {
match name.ctx {
ExprContext::Load => self.infer_name_load(name),
ExprContext::Store | ExprContext::Del => Type::None,
ExprContext::Store | ExprContext::Del => Type::Never,
ExprContext::Invalid => Type::Unknown,
}
}
Expand Down Expand Up @@ -2533,7 +2533,7 @@ impl<'db> TypeInferenceBuilder<'db> {
ExprContext::Load => self.infer_attribute_load(attribute),
ExprContext::Store | ExprContext::Del => {
self.infer_expression(value);
Type::None
Type::Never
}
ExprContext::Invalid => {
self.infer_expression(value);
Expand Down
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