fix "no constructor defined" messages on PyPy (#5329)

* fix "cannot create '%s' instances" message to match CPython

* don't use unlimited C API directly

* review feedback

* fixup

* fixup xfail on PyPy

Author: davidhewitt

pytests/tests/test_pyclasses.py

@@ -96,8 +96,8 @@ def __new__(cls):
 
 
 @pytest.mark.xfail(
-    platform.python_implementation() == "PyPy" and sys.version_info < (3, 11),
-    reason="broken on older PyPy due to https://github.com/pypy/pypy/issues/5319 on supported PyPy",
+    platform.python_implementation() == "PyPy" and sys.version_info[:2] == (3, 11),
+    reason="broken on PyPy 3.11 due to https://github.com/pypy/pypy/issues/5319, waiting for next release",
 )
 @pytest.mark.parametrize(
     "cls, exc_message",

src/pyclass/create_type_object.rs

@@ -437,14 +437,13 @@ impl PyTypeBuilder {
         unsafe { self.push_slot(ffi::Py_tp_base, self.tp_base) }
 
         if !self.has_new {
-            // PyPy doesn't respect the flag
-            // https://github.com/pypy/pypy/issues/5318
-            #[cfg(not(all(Py_3_10, not(PyPy))))]
+            // Flag introduced in 3.10, only worked in PyPy on 3.11
+            #[cfg(not(any(all(Py_3_10, not(PyPy)), all(Py_3_11, PyPy))))]
             {
                 // Safety: This is the correct slot type for Py_tp_new
                 unsafe { self.push_slot(ffi::Py_tp_new, no_constructor_defined as *mut c_void) }
             }
-            #[cfg(all(Py_3_10, not(PyPy)))]
+            #[cfg(any(all(Py_3_10, not(PyPy)), all(Py_3_11, PyPy)))]
             {
                 self.class_flags |= ffi::Py_TPFLAGS_DISALLOW_INSTANTIATION;
             }
@@ -558,7 +557,7 @@ fn bpo_45315_workaround(py: Python<'_>, class_name: CString) {
 }
 
 /// Default new implementation
-#[cfg(not(all(Py_3_10, not(PyPy))))]
+#[cfg(not(any(all(Py_3_10, not(PyPy)), all(Py_3_11, PyPy))))]
 unsafe extern "C" fn no_constructor_defined(
     subtype: *mut ffi::PyTypeObject,
     _args: *mut ffi::PyObject,
@@ -567,29 +566,15 @@ unsafe extern "C" fn no_constructor_defined(
     unsafe {
         trampoline(|py| {
             let tpobj = PyType::from_borrowed_type_ptr(py, subtype);
-            #[cfg(not(PyPy))]
-            {
-                // unlike `fully_qualified_name`, this always include the module
-                let module = tpobj
-                    .module()
-                    .map_or_else(|_| "<unknown>".into(), |s| s.to_string());
-                let qualname = tpobj.qualname();
-                let qualname = qualname.map_or_else(|_| "<unknown>".into(), |s| s.to_string());
-                Err(crate::exceptions::PyTypeError::new_err(format!(
-                    "cannot create '{module}.{qualname}' instances"
-                )))
-            }
-            #[cfg(PyPy)]
-            {
-                // https://github.com/pypy/pypy/issues/5319
-                // .qualname() seems wrong on PyPy, includes the module already
-                let full_name = tpobj
-                    .qualname()
-                    .map_or_else(|_| "<unknown>".into(), |s| s.to_string());
-                Err(crate::exceptions::PyTypeError::new_err(format!(
-                    "cannot create '{full_name}' instances"
-                )))
-            }
+            // unlike `fully_qualified_name`, this always include the module
+            let module = tpobj
+                .module()
+                .map_or_else(|_| "<unknown>".into(), |s| s.to_string());
+            let qualname = tpobj.qualname();
+            let qualname = qualname.map_or_else(|_| "<unknown>".into(), |s| s.to_string());
+            Err(crate::exceptions::PyTypeError::new_err(format!(
+                "cannot create '{module}.{qualname}' instances"
+            )))
         })
     }
 }