Added upb::FileDef, which represents the file defs are declared in.

It is entirely optional: MessageDef/EnumDef can still exist
on their own.  But this can represent a def's file when it is
desirable to do so (eg. for code generators).

This approach will require that we change the way we handle
extensions.  But I think it will be a good change overall.

Specifically, we previously handled extensions by duplicating
the extended message and then adding the extension as a regular
field to the duplicated message.  This required also duplicating
any messages that could reach the extended message.

In the new world we will need a way of declaring and looking up
extensions separately from the message being extended.

This change also involves some notable changes to the generated
code:

- files are now called foo.upbdefs.h instead of foo.upb.h.
  This reflects the fact that we might possibly generate several
  different output files for a .proto file, and this one is just
  for defs.

- we no longer generate selectors in the .h file.

- the upbdefs.c no longer vends a SymbolTable.  Now it vends the
  individual messages (and possibly a FileDef later).  I think this
  will compose better once we can generate files where one
  generated files imports another.

We also make the descriptor reader vend a list of FileDefs now.
This is the best conceptual match for parsing a FileDescriptorSet.

1 files changed, 4 insertions, 5 deletions

diff --git a/tests/test_handlers.c b/tests/test_handlers.c
index b591ad2..fe6fb82 100644
--- a/tests/test_handlers.c
+++ b/tests/test_handlers.c
@@ -1,6 +1,6 @@
 
 #include "upb/handlers.h"
-#include "upb/descriptor/descriptor.upb.h"
+#include "upb/descriptor/descriptor.upbdefs.h"
 #include "upb_test.h"
 #include <stdlib.h>
 #include <string.h>
@@ -13,10 +13,9 @@ static bool startmsg(void *c, const void *hd) {
 
 static void test_error() {
   /* Test creating handlers of a static msgdef. */
-  const upb_symtab *s = upbdefs_google_protobuf_descriptor(&s);
-  upb_handlers *h =
-      upb_handlers_new(upbdefs_google_protobuf_DescriptorProto(s), &h);
-  upb_symtab_unref(s, &s);
+  const upb_msgdef *m = upbdefs_google_protobuf_DescriptorProto_get(&m);
+  upb_handlers *h = upb_handlers_new(m, &h);
+  upb_msgdef_unref(m, &m);
 
   /* Attempt to set the same handler twice causes error. */
   ASSERT(upb_ok(upb_handlers_status(h)));