py/vm: Don't emit warning when using "raise ... from None".

"Raise SomeException() from None" is a common Python idiom to suppress
chained exceptions and thus shouldn't trigger a warning on a version of
Python that doesn't support them in the first place.

1 files changed, 4 insertions, 2 deletions

diff --git a/py/vm.c b/py/vm.c
index 385d13ee4..a7902d927 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -1171,8 +1171,10 @@ unwind_return:
 
                 ENTRY(MP_BC_RAISE_FROM): {
                     MARK_EXC_IP_SELECTIVE();
-                    mp_warning(NULL, "exception chaining not supported");
-                    sp--; // ignore (pop) "from" argument
+                    mp_obj_t from_value = POP();
+                    if (from_value != mp_const_none) {
+                        mp_warning(NULL, "exception chaining not supported");
+                    }
                     mp_obj_t obj = mp_make_raise_obj(TOP());
                     RAISE(obj);
                 }