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, 13 insertions, 2 deletions

diff --git a/tests/test_cpp.cc b/tests/test_cpp.cc
index 48f0a3f..c27526b 100644
--- a/tests/test_cpp.cc
+++ b/tests/test_cpp.cc
@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include <fstream>
 #include <iostream>
 #include <set>
 #include <sstream>
@@ -144,12 +145,22 @@ static void TestCastsConst10() {
 }
 
 static void TestSymbolTable(const char *descriptor_file) {
-  upb::reffed_ptr<upb::SymbolTable> s(upb::SymbolTable::New());
   upb::Status status;
-  if (!upb::LoadDescriptorFileIntoSymtab(s.get(), descriptor_file, &status)) {
+  std::ifstream file_in(descriptor_file, std::ios::binary);
+  std::string descriptor((std::istreambuf_iterator<char>(file_in)),
+                         (std::istreambuf_iterator<char>()));
+  std::vector<upb::reffed_ptr<upb::FileDef> > files;
+  if (!upb::LoadDescriptor(descriptor, &status, &files)) {
     std::cerr << "Couldn't load descriptor: " << status.error_message();
     exit(1);
   }
+
+  upb::reffed_ptr<upb::SymbolTable> s(upb::SymbolTable::New());
+
+  for (size_t i = 0; i < files.size(); i++) {
+    ASSERT(s->AddFile(files[i].get(), &status));
+  }
+
   ASSERT(!s->IsFrozen());
   s->Freeze();
   ASSERT(s->IsFrozen());