all: Simplify buffer protocol to just a "get buffer" callback.

The buffer protocol type only has a single member, and this existing layout
creates problems for the upcoming split/slot-index mp_obj_type_t layout
optimisations.

If we need to make the buffer protocol more sophisticated in the future
either we can rely on the mp_obj_type_t optimisations to just add
additional slots to mp_obj_type_t or re-visit the buffer protocol then.

This change is a no-op in terms of generated code.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/obj.c

@@ -579,10 +579,10 @@ mp_obj_t mp_identity_getiter(mp_obj_t self, mp_obj_iter_buf_t *iter_buf) {
 
 bool mp_get_buffer(mp_obj_t obj, mp_buffer_info_t *bufinfo, mp_uint_t flags) {
     const mp_obj_type_t *type = mp_obj_get_type(obj);
-    if (type->buffer_p.get_buffer == NULL) {
+    if (type->buffer == NULL) {
         return false;
     }
-    int ret = type->buffer_p.get_buffer(obj, bufinfo, flags);
+    int ret = type->buffer(obj, bufinfo, flags);
     if (ret != 0) {
         return false;
     }

py/obj.h

@@ -557,9 +557,7 @@ typedef struct _mp_buffer_info_t {
 #define MP_BUFFER_READ  (1)
 #define MP_BUFFER_WRITE (2)
 #define MP_BUFFER_RW (MP_BUFFER_READ | MP_BUFFER_WRITE)
-typedef struct _mp_buffer_p_t {
-    mp_int_t (*get_buffer)(mp_obj_t obj, mp_buffer_info_t *bufinfo, mp_uint_t flags);
-} mp_buffer_p_t;
+typedef mp_int_t (*mp_buffer_fun_t)(mp_obj_t obj, mp_buffer_info_t *bufinfo, mp_uint_t flags);
 bool mp_get_buffer(mp_obj_t obj, mp_buffer_info_t *bufinfo, mp_uint_t flags);
 void mp_get_buffer_raise(mp_obj_t obj, mp_buffer_info_t *bufinfo, mp_uint_t flags);
 
@@ -618,7 +616,7 @@ struct _mp_obj_type_t {
     mp_fun_1_t iternext;
 
     // Implements the buffer protocol if supported by this type.
-    mp_buffer_p_t buffer_p;
+    mp_buffer_fun_t buffer;
 
     // One of disjoint protocols (interfaces), like mp_stream_p_t, etc.
     const void *protocol;

py/objarray.c

@@ -580,7 +580,7 @@ const mp_obj_type_t mp_type_array = {
     .unary_op = array_unary_op,
     .binary_op = array_binary_op,
     .subscr = array_subscr,
-    .buffer_p = { .get_buffer = array_get_buffer },
+    .buffer_p = array_get_buffer,
     .locals_dict = (mp_obj_dict_t *)&mp_obj_array_locals_dict,
 };
 #endif
@@ -596,7 +596,7 @@ const mp_obj_type_t mp_type_bytearray = {
     .unary_op = array_unary_op,
     .binary_op = array_binary_op,
     .subscr = array_subscr,
-    .buffer_p = { .get_buffer = array_get_buffer },
+    .buffer = array_get_buffer,
     .locals_dict = (mp_obj_dict_t *)&mp_obj_bytearray_locals_dict,
 };
 #endif
@@ -617,7 +617,7 @@ const mp_obj_type_t mp_type_memoryview = {
     .locals_dict = (mp_obj_dict_t *)&mp_obj_memoryview_locals_dict,
     #endif
     .subscr = array_subscr,
-    .buffer_p = { .get_buffer = array_get_buffer },
+    .buffer = array_get_buffer,
 };
 #endif
 

py/objstr.c

@@ -2151,7 +2151,7 @@ const mp_obj_type_t mp_type_str = {
     .binary_op = mp_obj_str_binary_op,
     .subscr = bytes_subscr,
     .getiter = mp_obj_new_str_iterator,
-    .buffer_p = { .get_buffer = mp_obj_str_get_buffer },
+    .buffer = mp_obj_str_get_buffer,
     .locals_dict = (mp_obj_dict_t *)&mp_obj_str_locals_dict,
 };
 #endif // !MICROPY_PY_BUILTINS_STR_UNICODE
@@ -2165,7 +2165,7 @@ const mp_obj_type_t mp_type_bytes = {
     .binary_op = mp_obj_str_binary_op,
     .subscr = bytes_subscr,
     .getiter = mp_obj_new_bytes_iterator,
-    .buffer_p = { .get_buffer = mp_obj_str_get_buffer },
+    .buffer = mp_obj_str_get_buffer,
     .locals_dict = (mp_obj_dict_t *)&mp_obj_bytes_locals_dict,
 };
 

py/objstrunicode.c

@@ -238,7 +238,7 @@ const mp_obj_type_t mp_type_str = {
     .binary_op = mp_obj_str_binary_op,
     .subscr = str_subscr,
     .getiter = mp_obj_new_str_iterator,
-    .buffer_p = { .get_buffer = mp_obj_str_get_buffer },
+    .buffer = mp_obj_str_get_buffer,
     .locals_dict = (mp_obj_dict_t *)&mp_obj_str_locals_dict,
 };
 

py/objtype.c

@@ -913,14 +913,14 @@ STATIC mp_int_t instance_get_buffer(mp_obj_t self_in, mp_buffer_info_t *bufinfo,
     struct class_lookup_data lookup = {
         .obj = self,
         .attr = MP_QSTR_, // don't actually look for a method
-        .meth_offset = offsetof(mp_obj_type_t, buffer_p.get_buffer),
+        .meth_offset = offsetof(mp_obj_type_t, buffer),
         .dest = member,
         .is_type = false,
     };
     mp_obj_class_lookup(&lookup, self->base.type);
     if (member[0] == MP_OBJ_SENTINEL) {
         const mp_obj_type_t *type = mp_obj_get_type(self->subobj[0]);
-        return type->buffer_p.get_buffer(self->subobj[0], bufinfo, flags);
+        return type->buffer(self->subobj[0], bufinfo, flags);
     } else {
         return 1; // object does not support buffer protocol
     }
@@ -1160,7 +1160,7 @@ mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict)
     o->subscr = instance_subscr;
     o->getiter = mp_obj_instance_getiter;
     // o->iternext = ; not implemented
-    o->buffer_p.get_buffer = instance_get_buffer;
+    o->buffer = instance_get_buffer;
 
     if (bases_len > 0) {
         // Inherit protocol from a base class. This allows to define an