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[ty] only issue redundant-cast on fully static types

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Carl Meyer 2025-05-12 15:59:29 -07:00
parent 0d6fafd0f9
commit 2736e87b2c
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2 changed files with 7 additions and 17 deletions
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18
crates/ty_python_semantic/resources/mdtest/directives/cast.md
View file

@ -31,12 +31,6 @@ def function_returning_int() -> int:
# error: [redundant-cast] "Value is already of type `int`"
cast(int, function_returning_int())
def function_returning_any() -> Any:
return "blah"
# error: [redundant-cast] "Value is already of type `Any`"
cast(Any, function_returning_any())
```
Complex type expressions (which may be unsupported) do not lead to spurious `[redundant-cast]`
@ -50,11 +44,8 @@ def f(x: Callable[[dict[str, int]], None], y: tuple[dict[str, int]]):
b = cast(tuple[list[bytes]], y)
```
A cast from `Todo` or `Unknown` to `Any` is not considered a "redundant cast": even if these are
understood as gradually equivalent types by ty, they are understood as different types by human
readers of ty's output. For `Unknown` in particular, we may consider it differently in the context
of some opt-in diagnostics, as it indicates that the gradual type has come about due to an invalid
annotation, missing annotation or missing type argument somewhere.
Casting `Unknown` to `Unknown` or `Any` to `Any` is not considered redundant; these dynamic types
may represent different static types, and erroring on this violates the gradual guarantee.
```py
from ty_extensions import Unknown
@ -66,5 +57,8 @@ def f(x: Any, y: Unknown, z: Any | str | int):
b = cast(Any, y)
reveal_type(b) # revealed: Any
c = cast(str | int | Any, z) # error: [redundant-cast]
c = cast(str | int | Any, z)
d = cast(y, y)
e = cast(x, x)
```

6
crates/ty_python_semantic/src/types/infer.rs
View file

@ -4908,11 +4908,7 @@ impl<'db> TypeInferenceBuilder<'db> {
overload.parameter_types()
{
let db = self.db();
if (source_type.is_equivalent_to(db, *casted_type)
|| source_type.normalized(db)
== casted_type.normalized(db))
&& !source_type.contains_todo(db)
{
if source_type.is_equivalent_to(db, *casted_type) {
if let Some(builder) = self
.context
.report_lint(&REDUNDANT_CAST, call_expression)