Introduce upb_Message_SetBaseFieldMessage()

This just behaves the same as the pre-existing upb_Message_SetMessage(), but with the intendended naming style (upb_Message_SetMessage should accept an arena and support extensions).

PiperOrigin-RevId: 667998428

upb/message/accessors.h

diff --git a/upb/message/accessors.h b/upb/message/accessors.h
index 922026e..613f634 100644
--- a/upb/message/accessors.h
+++ b/upb/message/accessors.h
@@ -8,6 +8,8 @@
 #ifndef UPB_MESSAGE_ACCESSORS_H_
 #define UPB_MESSAGE_ACCESSORS_H_
 
+#include <stdint.h>
+
 #include "upb/base/string_view.h"
 #include "upb/mem/arena.h"
 #include "upb/message/array.h"
@@ -150,6 +152,10 @@
                                                   const upb_MiniTableField* f,
                                                   int64_t value);
 
+UPB_API_INLINE void upb_Message_SetBaseFieldMessage(struct upb_Message* msg,
+                                                    const upb_MiniTableField* f,
+                                                    upb_Message* value);
+
 UPB_API_INLINE void upb_Message_SetBaseFieldString(struct upb_Message* msg,
                                                    const upb_MiniTableField* f,
                                                    upb_StringView value);
@@ -222,6 +228,8 @@
                                          const upb_MiniTableField* f,
                                          int64_t value, upb_Arena* a);
 
+// Unlike the other similarly-named setters, this function can only be
+// called on base fields. Prefer upb_Message_SetBaseFieldMessage().
 UPB_API_INLINE void upb_Message_SetMessage(upb_Message* msg,
                                            const upb_MiniTableField* f,
                                            upb_Message* value);

upb/message/internal/accessors.h

diff --git a/upb/message/internal/accessors.h b/upb/message/internal/accessors.h
index 5bbfb1e..aae0fdc 100644
--- a/upb/message/internal/accessors.h
+++ b/upb/message/internal/accessors.h
@@ -639,6 +639,13 @@
   upb_Message_SetBaseField(msg, f, &value);
 }
 
+UPB_API_INLINE void upb_Message_SetBaseFieldMessage(struct upb_Message* msg,
+                                                    const upb_MiniTableField* f,
+                                                    struct upb_Message* value) {
+  UPB_PRIVATE(_upb_Message_SetTaggedMessagePtr)
+  (msg, f, UPB_PRIVATE(_upb_TaggedMessagePtr_Pack)(value, false));
+}
+
 UPB_API_INLINE void upb_Message_SetBaseFieldString(struct upb_Message* msg,
                                                    const upb_MiniTableField* f,
                                                    upb_StringView value) {
@@ -807,8 +814,8 @@
 UPB_API_INLINE void upb_Message_SetMessage(struct upb_Message* msg,
                                            const upb_MiniTableField* f,
                                            struct upb_Message* value) {
-  UPB_PRIVATE(_upb_Message_SetTaggedMessagePtr)
-  (msg, f, UPB_PRIVATE(_upb_TaggedMessagePtr_Pack)(value, false));
+  UPB_ASSERT(!upb_MiniTableField_IsExtension(f));
+  upb_Message_SetBaseFieldMessage(msg, f, value);
 }
 
 // Sets the value of a `string` or `bytes` field. The bytes of the value are not