Make OneofDef stop deriving from Def.

It is clear now that oneofs are different form other
defs in one important way: they are not top-level
constructs that can stand on their own in a SymbolTable,
for example.  If you are iterating over a list of Defs
in a SymbolTable, there is no chance you will run into
a oneof.  To reflect this reality, OneofDef no longer
derives from Def, and the UPB_DEF_ONEOF is no longer
an enum value that needs to be handled.

upb/def.c

@@ -538,7 +538,7 @@ static void visitfield(const upb_refcounted *r, upb_refcounted_visit *visit,
     visit(r, upb_msgdef_upcast2(upb_fielddef_containingtype(f)), closure);
   }
   if (upb_fielddef_containingoneof(f)) {
-    visit(r, upb_oneofdef_upcast2(upb_fielddef_containingoneof(f)), closure);
+    visit(r, upb_oneofdef_upcast(upb_fielddef_containingoneof(f)), closure);
   }
   if (upb_fielddef_subdef(f)) {
     visit(r, upb_def_upcast(upb_fielddef_subdef(f)), closure);
@@ -1300,7 +1300,7 @@ static void visitmsg(const upb_refcounted *r, upb_refcounted_visit *visit,
       !upb_msg_oneof_done(&o);
       upb_msg_oneof_next(&o)) {
     upb_oneofdef *f = upb_msg_iter_oneof(&o);
-    visit(r, upb_oneofdef_upcast2(f), closure);
+    visit(r, upb_oneofdef_upcast(f), closure);
   }
 }
 
@@ -1588,7 +1588,7 @@ static void freeoneof(upb_refcounted *r) {
   upb_oneofdef *o = (upb_oneofdef*)r;
   upb_strtable_uninit(&o->ntof);
   upb_inttable_uninit(&o->itof);
-  upb_def_uninit(upb_oneofdef_upcast_mutable(o));
+  free((void*)o->name);
   free(o);
 }
 
@@ -1597,9 +1597,9 @@ upb_oneofdef *upb_oneofdef_new(const void *owner) {
   upb_oneofdef *o = malloc(sizeof(*o));
   o->parent = NULL;
   if (!o) return NULL;
-  if (!upb_def_init(upb_oneofdef_upcast_mutable(o), UPB_DEF_ONEOF, &vtbl,
-                    owner))
+  if (!upb_refcounted_init(upb_oneofdef_upcast_mutable(o), &vtbl, owner))
     goto err2;
+  o->name = NULL;
   if (!upb_inttable_init(&o->itof, UPB_CTYPE_PTR)) goto err2;
   if (!upb_strtable_init(&o->ntof, UPB_CTYPE_PTR)) goto err1;
   return o;
@@ -1616,8 +1616,7 @@ upb_oneofdef *upb_oneofdef_dup(const upb_oneofdef *o, const void *owner) {
   upb_oneof_iter i;
   upb_oneofdef *newo = upb_oneofdef_new(owner);
   if (!newo) return NULL;
-  ok = upb_def_setfullname(upb_oneofdef_upcast_mutable(newo),
-                           upb_def_fullname(upb_oneofdef_upcast(o)), NULL);
+  ok = upb_oneofdef_setname(newo, upb_oneofdef_name(o), NULL);
   UPB_ASSERT_VAR(ok, ok);
   for (upb_oneof_begin(&i, o); !upb_oneof_done(&i); upb_oneof_next(&i)) {
     upb_fielddef *f = upb_fielddef_dup(upb_oneof_iter_field(&i), &f);
@@ -1629,17 +1628,18 @@ upb_oneofdef *upb_oneofdef_dup(const upb_oneofdef *o, const void *owner) {
   return newo;
 }
 
-const char *upb_oneofdef_name(const upb_oneofdef *o) {
-  return upb_def_fullname(upb_oneofdef_upcast(o));
-}
+const char *upb_oneofdef_name(const upb_oneofdef *o) { return o->name; }
 
-bool upb_oneofdef_setname(upb_oneofdef *o, const char *fullname,
-                             upb_status *s) {
+bool upb_oneofdef_setname(upb_oneofdef *o, const char *name, upb_status *s) {
+  assert(!upb_oneofdef_isfrozen(o));
   if (upb_oneofdef_containingtype(o)) {
     upb_status_seterrmsg(s, "oneof already added to a message");
     return false;
   }
-  return upb_def_setfullname(upb_oneofdef_upcast_mutable(o), fullname, s);
+  if (!upb_isident(name, strlen(name), true, s)) return false;
+  free((void*)o->name);
+  o->name = upb_strdup(name);
+  return true;
 }
 
 const upb_msgdef *upb_oneofdef_containingtype(const upb_oneofdef *o) {

upb/def.h

@@ -37,6 +37,8 @@ class OneofDef;
 #endif
 
 UPB_DECLARE_DERIVED_TYPE(upb::Def, upb::RefCounted, upb_def, upb_refcounted)
+UPB_DECLARE_DERIVED_TYPE(upb::OneofDef, upb::RefCounted, upb_oneofdef,
+                         upb_refcounted)
 
 /* The maximum message depth that the type graph can have.  This is a resource
  * limit for the C stack since we sometimes need to recursively traverse the
@@ -48,15 +50,16 @@ UPB_DECLARE_DERIVED_TYPE(upb::Def, upb::RefCounted, upb_def, upb_refcounted)
 #define UPB_MAX_MESSAGE_DEPTH 64
 
 
-/* upb::Def: base class for defs  *********************************************/
+/* upb::Def: base class for top-level defs  ***********************************/
 
-/* All the different kind of defs we support.  These correspond 1:1 with
- * declarations in a .proto file. */
+/* All the different kind of defs that can be defined at the top-level and put
+ * in a SymbolTable or appear in a FileDef::defs() list.  This excludes some
+ * defs (like oneofs and files).  It only includes fields because they can be
+ * defined as extensions. */
 typedef enum {
   UPB_DEF_MSG,
   UPB_DEF_FIELD,
   UPB_DEF_ENUM,
-  UPB_DEF_ONEOF,
   UPB_DEF_SERVICE,   /* Not yet implemented. */
   UPB_DEF_ANY = -1   /* Wildcard for upb_symtab_get*() */
 } upb_deftype_t;
@@ -190,7 +193,6 @@ UPB_END_EXTERN_C
 UPB_DECLARE_DEF_TYPE(upb::FieldDef, fielddef, FIELD)
 UPB_DECLARE_DEF_TYPE(upb::MessageDef, msgdef, MSG)
 UPB_DECLARE_DEF_TYPE(upb::EnumDef, enumdef, ENUM)
-UPB_DECLARE_DEF_TYPE(upb::OneofDef, oneofdef, ONEOF)
 
 #undef UPB_DECLARE_DEF_TYPE
 #undef UPB_DEF_CASTS
@@ -1226,7 +1228,7 @@ upb_oneofdef *upb_oneofdef_new(const void *owner);
 upb_oneofdef *upb_oneofdef_dup(const upb_oneofdef *o, const void *owner);
 
 /* Include upb_refcounted methods like upb_oneofdef_ref(). */
-UPB_REFCOUNTED_CMETHODS(upb_oneofdef, upb_oneofdef_upcast2)
+UPB_REFCOUNTED_CMETHODS(upb_oneofdef, upb_oneofdef_upcast)
 
 const char *upb_oneofdef_name(const upb_oneofdef *o);
 bool upb_oneofdef_setname(upb_oneofdef *o, const char *name, upb_status *s);

upb/structdefs.int.h

@@ -150,15 +150,16 @@ struct upb_enumdef {
 /* upb_oneofdef ***************************************************************/
 
 struct upb_oneofdef {
-  upb_def base;
+  upb_refcounted base;
 
+  const char *name;
   upb_strtable ntof;
   upb_inttable itof;
   const upb_msgdef *parent;
 };
 
 #define UPB_ONEOFDEF_INIT(name, ntof, itof, refs, ref2s) \
-  { UPB_DEF_INIT(name, UPB_DEF_ENUM, refs, ref2s), ntof, itof }
+  { UPB_REFCOUNT_INIT(refs, ref2s), name, ntof, itof }
 
 
 /* upb_symtab *****************************************************************/