upb: upb_Message_ExtensionByIndex() no longer returns a (upb_Extension*)

PiperOrigin-RevId: 600926618

upb/message/compat.c

@@ -17,13 +17,13 @@
 // Must be last.
 #include "upb/port/def.inc"
 
-const upb_Extension* upb_Message_ExtensionByIndex(const upb_Message* msg,
-                                                  size_t index) {
+const upb_MiniTableExtension* upb_Message_ExtensionByIndex(
+    const upb_Message* msg, size_t index) {
   size_t count;
   const upb_Extension* ext = UPB_PRIVATE(_upb_Message_Getexts)(msg, &count);
 
   UPB_ASSERT(index < count);
-  return &ext[index];
+  return ext[index].ext;
 }
 
 const upb_Extension* upb_Message_FindExtensionByNumber(const upb_Message* msg,

upb/message/compat.h

@@ -11,6 +11,7 @@
 #include <stdint.h>
 
 #include "upb/message/message.h"
+#include "upb/mini_table/extension.h"
 
 // Must be last.
 #include "upb/port/def.inc"
@@ -24,8 +25,8 @@
 extern "C" {
 #endif
 
-const upb_Extension* upb_Message_ExtensionByIndex(const upb_Message* msg,
-                                                  size_t index);
+const upb_MiniTableExtension* upb_Message_ExtensionByIndex(
+    const upb_Message* msg, size_t index);
 
 // Returns the extension with the given field number, or NULL on failure.
 const upb_Extension* upb_Message_FindExtensionByNumber(const upb_Message* msg,