Introspection: expose #[classattribute] as an attribute (#5839)

* Introspection: expose `#[classattribute]` as an attribute

Outputs valid but a bit too broad stubs

Combining @classmethod and @Property has been removed in 3.13

* Add Final

Author: Tpt

newsfragments/5839.changed.md

@@ -0,0 +1 @@
+Stubs: emit `#[classattribute]` as plain Python class attributes and not functions annotated with `@classattribute` and `@property` (not supported since 3.13)

pyo3-macros-backend/src/pyimpl.rs

@@ -26,7 +26,7 @@ use syn::{
     ImplItemFn, Result,
 };
 #[cfg(feature = "experimental-inspect")]
-use syn::{parse_quote, Ident};
+use syn::{parse_quote, Ident, ReturnType};
 
 /// The mechanism used to collect `#[pymethods]` into the type object
 #[derive(Copy, Clone)]
@@ -462,10 +462,20 @@ pub fn method_introspection_code(
         }
         FnType::FnModule(_) => (), // TODO: not sure this can happen
         FnType::ClassAttribute => {
-            first_argument = Some("cls");
-            // TODO: this combination only works with Python 3.9-3.11 https://docs.python.org/3.11/library/functions.html#classmethod
-            decorators.push(PyExpr::builtin("classmethod"));
-            decorators.push(PyExpr::builtin("property"));
+            // We return an attribute because there is no decorator for this case
+            return attribute_introspection_code(
+                pyo3_path,
+                Some(parent),
+                name,
+                PyExpr::ellipsis(),
+                if let ReturnType::Type(_, t) = &spec.output {
+                    (**t).clone()
+                } else {
+                    parse_quote!(#pyo3_path::Py<#pyo3_path::types::PyNone>)
+                },
+                get_doc(attrs, None).as_ref(),
+                true,
+            );
         }
     }
     let return_type = if spec.python_name == "__new__" {

pytests/noxfile.py

@@ -49,16 +49,13 @@ def mypy(session: nox.Session):
         session.install(".[dev]")
 
         # TODO: remove --disable-error-code", "override" when __eq__ and __ne__ will always take object for input
-        # TODO: remove "--disable-error-code", "misc" when #[classattr] will be properly emitted
         session.run_always(
             "python",
             "-m",
             "mypy",
             "tests",
             "--disable-error-code",
             "override",
-            "--disable-error-code",
-            "misc",
         )
         # TODO: enable stubtest when previously listed errors will be fixed session.run_always("python", "-m", "mypy.stubtest", "pyo3_pytests")
     finally:

pytests/stubs/pyclasses.pyi

@@ -1,5 +1,5 @@
 from _typeshed import Incomplete
-from typing import final
+from typing import Final, final
 
 class AssertingBaseClass:
     """
@@ -9,6 +9,10 @@ class AssertingBaseClass:
 
 @final
 class ClassWithDecorators:
+    cls_attribute: Final[int]
+    """
+    A class attribute
+    """
     def __new__(cls, /) -> ClassWithDecorators: ...
     @property
     def attr(self, /) -> int:
@@ -26,12 +30,6 @@ class ClassWithDecorators:
         A setter
         """
     @classmethod
-    @property
-    def cls_attribute(cls, /) -> int:
-        """
-        A class attribute
-        """
-    @classmethod
     def cls_method(cls, /) -> int:
         """
         A class method