Fixed handling of exceptions raised in __del__ methods.

Author: advait-dixit

mypyc/codegen/emitclass.py

@@ -819,9 +819,19 @@ def generate_finalize_for_class(
             del_method.cname(emitter.names),
         )
     )
-    emitter.emit_line("if (type != NULL) {")
-    emitter.emit_line("PyErr_Restore(type, value, traceback);")
+    emitter.emit_line("if (PyErr_Occurred() != NULL) {")
+    emitter.emit_line('PyObject *class_obj = PyObject_GetAttrString(self, "__class__");')
+    emitter.emit_line('PyObject *del_method = PyObject_GetAttrString(class_obj, "__del__");')
+    # CPython interpreter uses PyErr_WriteUnraisable: https://docs.python.org/3/c-api/exceptions.html#c.PyErr_WriteUnraisable
+    # However, the message is slightly different due to the way mypyc compiles classes.
+    # CPython interpreter prints: Exception ignored in: <function F.__del__ at 0x100aed940>
+    # mypyc prints: Exception ignored in: <slot wrapper '__del__' of 'F' objects>
+    emitter.emit_line("PyErr_WriteUnraisable(del_method);")
+    emitter.emit_line("Py_DECREF(class_obj);")
+    emitter.emit_line("Py_XDECREF(del_method);")
     emitter.emit_line("}")
+    # PyErr_Restore also clears exception raised in __del__.
+    emitter.emit_line("PyErr_Restore(type, value, traceback);")
     emitter.emit_line("}")
 
 

mypyc/test-data/run-classes.test

@@ -2781,3 +2781,22 @@ gc.collect()
 [out]
 deleting C1...
 deleting C2...
+
+[case testDelException]
+# The error message in the expected output of this test does not match CPython's error message due to the way mypyc compiles Python classes. If the error message is fixed, the expected output of this test will also change.
+class F:
+    def __del__(self):
+        if True:
+            raise Exception("e2")
+
+[file driver.py]
+import native
+f = native.F()
+del f
+
+[out]
+Exception ignored in: <slot wrapper '__del__' of 'F' objects>
+Traceback (most recent call last):
+  File "native.py", line 5, in __del__
+    raise Exception("e2")
+Exception: e2