py/objnamedtuple: Fix segfault with empty namedtuple.

The empty tuple is usually a constant object, but named tuples must be
allocated to allow modification.  Added explicit allocation to fix this.

Also added a regression test to verify creating an empty named tuple works.

Fixes issue #7870.

Signed-off-by: Lars Haulin <lars.haulin@gmail.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/py/objnamedtuple.c b/py/objnamedtuple.c
index 214cad2572..b212993506 100644
--- a/py/objnamedtuple.c
+++ b/py/objnamedtuple.c
@@ -108,9 +108,10 @@ STATIC mp_obj_t namedtuple_make_new(const mp_obj_type_t *type_in, size_t n_args,
         #endif
     }
 
-    // Create a tuple and set the type to this namedtuple
-    mp_obj_tuple_t *tuple = MP_OBJ_TO_PTR(mp_obj_new_tuple(num_fields, NULL));
-    tuple->base.type = type_in;
+    // Create a namedtuple with explicit malloc. Calling mp_obj_new_tuple
+    // with num_fields=0 returns a read-only object.
+    mp_obj_tuple_t *tuple = mp_obj_malloc_var(mp_obj_tuple_t, mp_obj_t, num_fields, type_in);
+    tuple->len = num_fields;
 
     // Copy the positional args into the first slots of the namedtuple
     memcpy(&tuple->items[0], args, sizeof(mp_obj_t) * n_args);