Fix a SystemError if unboxing fails in a ufunc

Previously the conversion function could be called while an error was in flight, which isn't legal.

numba/np/ufunc/wrappers.py

@@ -57,10 +57,10 @@ def _build_ufunc_loop_body_objmode(load, store, context, func, builder,
         # Release owned reference to arguments
         for elem in elems:
             pyapi.decref(elem)
-    # NOTE: if an error occurred, it will be caught by the Numpy machinery
+        # NOTE: if an error occurred, it will be caught by the Numpy machinery
 
-    # Store
-    store(retval)
+        # Store. This may error too when unboxing.
+        store(retval)
 
     # increment indices
     for off, ary in zip(offsets, arrays):

numba/tests/npyufunc/test_errors.py

@@ -34,6 +34,17 @@ def power(a, b):
     return a ** b
 
 
+class BadType:
+    def __int__(self):
+        raise TypeError()
+
+
+def bad_type_if_odd(a):
+    if a % 2 == 0:
+        return a
+    return BadType()
+
+
 class TestExceptions(TestCase):
     """
     Test raising exceptions inside ufuncs.
@@ -55,6 +66,15 @@ def test_ufunc_raise(self):
     def test_ufunc_raise_objmode(self):
         self.check_ufunc_raise(forceobj=True)
 
+    def test_ufunc_conversion_raise_objmode(self):
+        f = vectorize(['int64(int64)'], forceobj=True)(bad_type_if_odd)
+        arr = np.array([10, 11, 12, 13], dtype=np.int64)
+        out = np.zeros_like(arr)
+        with self.assertRaises(TypeError) as cm:
+            f(arr, out)
+        # All values were computed except for the ones giving an error
+        self.assertEqual(list(out), [10, 0, 12, 0])
+
     def check_gufunc_raise(self, **vectorize_args):
         f = guvectorize(['int32[:], int32[:], int32[:]'], '(n),()->(n)',
                         **vectorize_args)(gufunc_foo)