Fix compile error when trying to use static slot methods

pyo3-macros-backend/src/pymethod.rs

@@ -1195,9 +1195,10 @@ fn generate_method_body(
     return_mode: Option<&ReturnMode>,
 ) -> Result<TokenStream> {
     let self_conversion = spec.tp.self_conversion(Some(cls), extract_error_mode);
+    let self_arg = spec.tp.self_arg();
     let rust_name = spec.name;
     let args = extract_proto_arguments(py, spec, arguments, extract_error_mode)?;
-    let call = quote! { _pyo3::callback::convert(#py, #cls::#rust_name(_slf, #(#args),*)) };
+    let call = quote! { _pyo3::callback::convert(#py, #cls::#rust_name(#self_arg #(#args),*)) };
     let body = if let Some(return_mode) = return_mode {
         return_mode.return_call_output(py, call)
     } else {

tests/test_static_slots.rs

@@ -0,0 +1,57 @@
+#![cfg(feature = "macros")]
+
+use pyo3::exceptions::PyIndexError;
+use pyo3::prelude::*;
+use pyo3::types::IntoPyDict;
+
+use pyo3::py_run;
+
+mod common;
+
+#[pyclass]
+struct Vector3 {
+    elements: [f64; 3],
+}
+
+#[pymethods]
+impl Vector3 {
+    #[new]
+    fn new(x: f64, y: f64, z: f64) -> Self {
+        Self {
+            elements: [x, y, z],
+        }
+    }
+
+    #[staticmethod]
+    fn __len__() -> usize {
+        3
+    }
+
+    fn __getitem__(&self, idx: isize) -> PyResult<f64> {
+        self.elements
+            .get(idx as usize)
+            .copied()
+            .ok_or_else(|| PyIndexError::new_err("list index out of range"))
+    }
+
+    fn __setitem__(&mut self, idx: isize, value: f64) {
+        self.elements[idx as usize] = value;
+    }
+}
+
+/// Return a dict with `s = Vector3(1, 2, 3)`.
+fn seq_dict(py: Python<'_>) -> &pyo3::types::PyDict {
+    let d = [("Vector3", py.get_type::<Vector3>())].into_py_dict(py);
+    // Though we can construct `s` in Rust, let's test `__new__` works.
+    py_run!(py, *d, "s = Vector3(1, 2, 3)");
+    d
+}
+
+#[test]
+fn test_len() {
+    Python::with_gil(|py| {
+        let d = seq_dict(py);
+
+        py_assert!(py, *d, "len(s) == 3");
+    });
+}