Merge pull request #251 from haberman/emptyfix

Fixed code generator for upbdefs when a file has no messages.

BUILD

@@ -389,11 +389,23 @@ cc_test(
     srcs = ["tests/test_generated_code.c"],
     deps = [
         ":test_messages_proto3_proto_upb",
+        ":empty_upbdefs_proto",
         ":test_upbproto",
         ":upb_test",
     ],
 )
 
+proto_library(
+    name = "empty_proto",
+    srcs = ["tests/empty.proto"],
+)
+
+upb_proto_reflection_library(
+    name = "empty_upbdefs_proto",
+    testonly = 1,
+    deps = [":empty_proto"],
+)
+
 upb_proto_library(
     name = "test_messages_proto3_proto_upb",
     testonly = 1,

tests/empty.proto

@@ -0,0 +1,2 @@
+syntax = "proto2";
+

upbc/generator.cc

@@ -853,12 +853,14 @@ void WriteDefSource(const protobuf::FileDescriptor* file, Output& output) {
   }
   output("\n");
 
+  if (!file_messages.empty()) {
     output("static const upb_msglayout *layouts[$0] = {\n", file_messages.size());
     for (auto message : file_messages) {
       output("  &$0,\n", MessageInit(message));
     }
     output("};\n");
     output("\n");
+  }
 
   protobuf::FileDescriptorProto file_proto;
   file->CopyTo(&file_proto);
@@ -905,7 +907,11 @@ void WriteDefSource(const protobuf::FileDescriptor* file, Output& output) {
 
   output("upb_def_init $0 = {\n", DefInitSymbol(file));
   output("  deps,\n");
+  if (file_messages.empty()) {
+    output("  NULL,\n");
+  } else {
     output("  layouts,\n");
+  }
   output("  \"$0\",\n", file->name());
   output("  UPB_STRVIEW_INIT(descriptor, $0)\n", file_data.size());
   output("};\n");