py/objtype: Allow passing keyword arguments to native base __init__.

Allowing passing keyword arguments to a native base's __init__, i.e.
`make_new` in the C code.  Previously only positional arguments were
allowed.

The main trade-off in this commit is that every call to the native base's
`make_new` is now going to be preceded by a call to
`mp_map_init_fixed_table` even though most of what that does is unused and
instead it merely serves as a way to pass the number of keyword arguments.

Fixes issue #15465.

Signed-off-by: stijn <stijn@ignitron.net>

3 files changed, 9 insertions, 4 deletions

diff --git a/py/obj.h b/py/obj.h
index eac2b89ea..d942e1bbf 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -516,6 +516,9 @@ typedef mp_obj_t (*mp_fun_3_t)(mp_obj_t, mp_obj_t, mp_obj_t);
 typedef mp_obj_t (*mp_fun_var_t)(size_t n, const mp_obj_t *);
 // mp_fun_kw_t takes mp_map_t* (and not const mp_map_t*) to ease passing
 // this arg to mp_map_lookup().
+// Note that the mp_obj_t* array will contain all arguments, positional and keyword, with the keyword
+// ones starting at offset n, like: arg0 arg1 ... arg<n> key0 value0 key1 value1 ..., and the mp_map_t*
+// gets those same keyword arguments but as a map for convenience; see fun_builtin_var_call.
 typedef mp_obj_t (*mp_fun_kw_t)(size_t n, const mp_obj_t *, mp_map_t *);
 
 // Flags for type behaviour (mp_obj_type_t.flags)
diff --git a/py/objfun.c b/py/objfun.c
index 8279605e9..0b1b8c115 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -107,7 +107,9 @@ static mp_obj_t fun_builtin_var_call(mp_obj_t self_in, size_t n_args, size_t n_k
     if (self->sig & 1) {
         // function allows keywords
 
-        // we create a map directly from the given args array
+        // we create a map directly from the given args array; self->fun.kw does still
+        // expect args to have both positional and keyword arguments, ordered as:
+        // arg0 arg1 ... arg<n_args> key0 value0 key1 value1 ... key<n_kw> value<n_kw>
         mp_map_t kw_args;
         mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
 
diff --git a/py/objtype.c b/py/objtype.c
index 16ff5310d..847216982 100644
--- a/py/objtype.c
+++ b/py/objtype.c
@@ -85,14 +85,14 @@ static int instance_count_native_bases(const mp_obj_type_t *type, const mp_obj_t
 
 // This wrapper function allows a subclass of a native type to call the
 // __init__() method (corresponding to type->make_new) of the native type.
-static mp_obj_t native_base_init_wrapper(size_t n_args, const mp_obj_t *args) {
+static mp_obj_t native_base_init_wrapper(size_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
     mp_obj_instance_t *self = MP_OBJ_TO_PTR(args[0]);
     const mp_obj_type_t *native_base = NULL;
     instance_count_native_bases(self->base.type, &native_base);
-    self->subobj[0] = MP_OBJ_TYPE_GET_SLOT(native_base, make_new)(native_base, n_args - 1, 0, args + 1);
+    self->subobj[0] = MP_OBJ_TYPE_GET_SLOT(native_base, make_new)(native_base, n_args - 1, kw_args->used, args + 1);
     return mp_const_none;
 }
-static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(native_base_init_wrapper_obj, 1, MP_OBJ_FUN_ARGS_MAX, native_base_init_wrapper);
+static MP_DEFINE_CONST_FUN_OBJ_KW(native_base_init_wrapper_obj, 1, native_base_init_wrapper);
 
 #if !MICROPY_CPYTHON_COMPAT
 static