Merge pull request RustPython#4168 from jopemachine/fix-testisinstance

Fix `test_infinite_recursion_via_bases_tuple`, `test_infinite_cycle_in_bases`

Author: youknowone

Lib/test/test_isinstance.py

@@ -316,7 +316,6 @@ def __bases__(self):
             self.assertRaises(RecursionError, issubclass, int, X())
             self.assertRaises(RecursionError, isinstance, 1, X())
 
-    @unittest.skip("TODO: RUSTPYTHON")
     def test_infinite_recursion_via_bases_tuple(self):
         """Regression test for bpo-30570."""
         class Failure(object):
@@ -326,7 +325,6 @@ def __getattr__(self, attr):
             with self.assertRaises(RecursionError):
                 issubclass(Failure(), int)
 
-    @unittest.skip("TODO: RUSTPYTHON")
     def test_infinite_cycle_in_bases(self):
         """Regression test for bpo-30570."""
         class X:

vm/src/protocol/object.rs

@@ -382,8 +382,11 @@ impl PyObject {
                     continue;
                 }
                 _ => {
-                    for i in 0..n {
-                        if let Ok(true) = tuple.fast_getitem(i).abstract_issubclass(cls, vm) {
+                    if let Some(i) = (0..n).next() {
+                        let check = vm.with_recursion("in abstract_issubclass", || {
+                            tuple.fast_getitem(i).abstract_issubclass(cls, vm)
+                        })?;
+                        if check {
                             return Ok(true);
                         }
                     }