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[ty] Treat Callables as bound-method descriptors in special cases (#20802)

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## Summary

Treat `Callable`s as bound-method descriptors if `Callable` is the
return type of a decorator that is applied to a function definition. See
the [rendered version of the new test
file](https://github.com/astral-sh/ruff/blob/david/callables-as-descriptors/crates/ty_python_semantic/resources/mdtest/call/callables_as_descriptors.md)
for the full description of this new heuristic.

I could imagine that we want to treat `Callable`s as bound-method
descriptors in other cases as well, but this seems like a step in the
right direction. I am planning to add other "use cases" from
https://github.com/astral-sh/ty/issues/491 to this test suite.

partially addresses https://github.com/astral-sh/ty/issues/491
closes https://github.com/astral-sh/ty/issues/1333

## Ecosystem impact

All positive

* 2961 removed `unsupported-operator` diagnostics on `sympy`, which was
one of the main motivations for implementing this change
* 37 removed `missing-argument` diagnostics, and no added call-error
diagnostics, which is an indicator that this heuristic shouldn't cause
many false positives
* A few removed `possibly-missing-attribute` diagnostics when accessing
attributes like `__name__` on decorated functions. The two added
`unused-ignore-comment` diagnostics are also cases of this.
* One new `invalid-assignment` diagnostic on `dd-trace-py`, which looks
suspicious, but only because our `invalid-assignment` diagnostics are
not great. This is actually a "Implicit shadowing of function"
diagnostic that hides behind the `invalid-assignment` diagnostic,
because a module-global function is being patched through a
`module.func` attribute assignment.

## Test Plan

New Markdown tests.
This commit is contained in:
David Peter 2025-10-13 21:17:47 +02:00 • committed by GitHub
parent d912f13661
commit 4b8e278a88
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3 changed files with 217 additions and 1 deletions
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7
crates/ty_python_semantic/src/types.rs
View file

@ -1014,6 +1014,13 @@ impl<'db> Type<'db> {
}
}
pub(crate) const fn unwrap_as_callable_type(self) -> Option<CallableType<'db>> {
match self {
Type::Callable(callable_type) => Some(callable_type),
_ => None,
}
}
pub(crate) const fn expect_dynamic(self) -> DynamicType<'db> {
self.into_dynamic()
.expect("Expected a Type::Dynamic variant")

21
crates/ty_python_semantic/src/types/infer/builder.rs
View file

@ -2175,7 +2175,26 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
.try_call(self.db(), &CallArguments::positional([inferred_ty]))
.map(|bindings| bindings.return_type(self.db()))
{
Ok(return_ty) => return_ty,
Ok(return_ty) => {
let is_input_function_like = inferred_ty
.into_callable(self.db())
.and_then(Type::unwrap_as_callable_type)
.is_some_and(|callable| callable.is_function_like(self.db()));
if is_input_function_like
&& let Some(callable_type) = return_ty.unwrap_as_callable_type()
{
// When a method on a class is decorated with a function that returns a `Callable`, assume that
// the returned callable is also function-like. See "Decorating a method with a `Callable`-typed
// decorator" in `callables_as_descriptors.md` for the extended explanation.
Type::Callable(CallableType::new(
self.db(),
callable_type.signatures(self.db()),
true,
))
} else {
return_ty
}
}
Err(CallError(_, bindings)) => {
bindings.report_diagnostics(&self.context, (*decorator_node).into());
bindings.return_type(self.db())