Revert class lookup (RustPython#7306)

youknowone · web-flow · commit 3865fdbf5bda · 2026-03-02T19:41:43.000+09:00
* Revert __class__ lookup skip in object_isinstance

The optimization to skip __class__ lookup based on getattro check
was incorrect: a class can override __class__ as a property while
still using standard __getattribute__. Revert to always performing
the lookup, matching CPython's object_isinstance behavior.

* Collapse nested if in object_isinstance for clippy
diff --git a/crates/vm/src/protocol/object.rs b/crates/vm/src/protocol/object.rs
@@ -4,8 +4,8 @@
 use crate::{
     AsObject, Py, PyObject, PyObjectRef, PyRef, PyResult, TryFromObject, VirtualMachine,
     builtins::{
-        PyBaseObject, PyBytes, PyDict, PyDictRef, PyGenericAlias, PyInt, PyList, PyStr, PyTuple,
-        PyTupleRef, PyType, PyTypeRef, PyUtf8Str, pystr::AsPyStr,
+        PyBytes, PyDict, PyDictRef, PyGenericAlias, PyInt, PyList, PyStr, PyTuple, PyTupleRef,
+        PyType, PyTypeRef, PyUtf8Str, pystr::AsPyStr,
     },
     common::{hash::PyHash, str::to_ascii},
     convert::{ToPyObject, ToPyResult},
@@ -580,18 +580,13 @@ impl PyObject {
         if let Ok(cls) = cls.try_to_ref::<PyType>(vm) {
             // PyType_Check(cls) - cls is a type object
             let mut retval = self.class().is_subtype(cls);
-            if !retval {
-                // __class__ is a data descriptor on object that always returns
-                // obj.class() under standard __getattribute__. Only do the
-                // expensive attribute lookup when getattro is overridden.
-                if !self.has_standard_getattro()
-                    && let Some(i_cls) =
-                        vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))?
-                    && let Ok(i_cls_type) = PyTypeRef::try_from_object(vm, i_cls)
-                    && !i_cls_type.is(self.class())
-                {
-                    retval = i_cls_type.is_subtype(cls);
-                }
+            if !retval
+                && let Some(i_cls) =
+                    vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))?
+                && let Ok(i_cls_type) = PyTypeRef::try_from_object(vm, i_cls)
+                && !i_cls_type.is(self.class())
+            {
+                retval = i_cls_type.is_subtype(cls);
             }
             Ok(retval)
         } else {
@@ -603,15 +598,13 @@ impl PyObject {
                 )
             })?;
 
-            let i_cls: PyObjectRef = if self.has_standard_getattro() {
-                self.class().to_owned().into()
+            if let Some(i_cls) =
+                vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))?
+            {
+                i_cls.abstract_issubclass(cls, vm)
             } else {
-                match vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))? {
-                    Some(cls) => cls,
-                    None => return Ok(false),
-                }
-            };
-            i_cls.abstract_issubclass(cls, vm)
+                Ok(false)
+            }
         }
     }
 
@@ -789,15 +782,6 @@ impl PyObject {
         Err(vm.new_type_error(format!("'{}' does not support item deletion", self.class())))
     }
 
-    /// Returns true if the object uses the standard `__getattribute__`
-    /// (i.e. `object.__getattribute__`), meaning attribute access follows
-    /// the normal descriptor protocol without custom interception.
-    #[inline]
-    fn has_standard_getattro(&self) -> bool {
-        let getattro = self.class().slots.getattro.load().unwrap();
-        getattro as usize == PyBaseObject::getattro as *const () as usize
-    }
-
     /// Equivalent to CPython's _PyObject_LookupSpecial
     /// Looks up a special method in the type's MRO without checking instance dict.
     /// Returns None if not found (masking AttributeError like CPython).
