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[ty] Remove incorrect type narrowing for if type(x) is C[int] (#19926)

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Alex Waygood 2025-08-15 17:52:14 +01:00 • committed by GitHub
parent f344dda82c
commit 9ced219ffc
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2 changed files with 52 additions and 6 deletions
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50
crates/ty_python_semantic/resources/mdtest/narrow/type.md
View file

@ -70,6 +70,56 @@ def _(x: A | B, y: A | C):
reveal_type(y) # revealed: A
```
## No narrowing for `type(x) is C[int]`
At runtime, `type(x)` will never return a generic alias object (only ever a class-literal object),
so no narrowing can occur if `type(x)` is compared with a generic alias object.
```toml
[environment]
python-version = "3.12"
```
```py
class A[T]: ...
class B: ...
def f(x: A[int] | B):
if type(x) is A[int]:
# this branch is actually unreachable -- we *could* reveal `Never` here!
reveal_type(x) # revealed: A[int] | B
else:
reveal_type(x) # revealed: A[int] | B
if type(x) is A:
# TODO: this should be `A[int]`, but `A[int] | B` would be better than `Never`
reveal_type(x) # revealed: Never
else:
reveal_type(x) # revealed: A[int] | B
if type(x) is B:
reveal_type(x) # revealed: B
else:
reveal_type(x) # revealed: A[int] | B
if type(x) is not A[int]:
reveal_type(x) # revealed: A[int] | B
else:
# this branch is actually unreachable -- we *could* reveal `Never` here!
reveal_type(x) # revealed: A[int] | B
if type(x) is not A:
reveal_type(x) # revealed: A[int] | B
else:
# TODO: this should be `A[int]`, but `A[int] | B` would be better than `Never`
reveal_type(x) # revealed: Never
if type(x) is not B:
reveal_type(x) # revealed: A[int] | B
else:
reveal_type(x) # revealed: B
```
## `type(x) == C`, `type(x) != C`
No narrowing can occur for equality comparisons, since there might be a custom `__eq__`

8
crates/ty_python_semantic/src/types/narrow.rs
View file

@ -756,12 +756,8 @@ impl<'db, 'ast> NarrowingConstraintsBuilder<'db, 'ast> {
node_index: _,
},
}) if keywords.is_empty() => {
let rhs_class = match rhs_ty {
Type::ClassLiteral(class) => class,
Type::GenericAlias(alias) => alias.origin(self.db),
_ => {
continue;
}
let Type::ClassLiteral(rhs_class) = rhs_ty else {
continue;
};
let target = match &**args {