Change where we rename Descriptor.cs to DescriptorProtoFile.cs.

We now do this in protoc instead of the generation simpler.

Benefits:
- Generation script is simpler
- Detection is simpler as we now only need to care about one filename
- The embedded descriptor knows itself as "google/protobuf/descriptor.proto" avoiding dependency issues

This PR also makes the "invalid dependency" exception clearer in terms of expected and actual dependencies.

csharp/generate_protos.sh

@@ -37,10 +37,8 @@ fi
 
 # Descriptor proto
 # TODO(jonskeet): Remove fixup
-cp src/google/protobuf/descriptor.proto src/google/protobuf/descriptor_proto_file.proto
 $PROTOC -Isrc --csharp_out=csharp/src/Google.Protobuf/Reflection \
-    src/google/protobuf/descriptor_proto_file.proto
-rm src/google/protobuf/descriptor_proto_file.proto
+    src/google/protobuf/descriptor.proto
 
 $PROTOC -Isrc --csharp_out=csharp/src/Google.Protobuf/WellKnownTypes \
     src/google/protobuf/any.proto \

csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs

@@ -301,7 +301,8 @@ namespace Google.Protobuf.Reflection
                 {
                     throw new DescriptorValidationException(result,
                         "Dependencies passed to FileDescriptor.BuildFrom() don't match " +
-                                                            "those listed in the FileDescriptorProto.");
+                        "those listed in the FileDescriptorProto. Expected: " +
+                        proto.Dependency[i] + " but was: " + dependencies[i].Name);
                 }
             }
 

src/google/protobuf/compiler/csharp/csharp_helpers.cc

@@ -118,6 +118,12 @@ std::string GetFileNamespace(const FileDescriptor* descriptor) {
 }
 
 std::string GetUmbrellaClassUnqualifiedName(const FileDescriptor* descriptor) {
+  // We manually rename Descriptor to DescriptorProtoFile to avoid collisions with
+  // the static Descriptor property. It would be nice to be able to do this with an
+  // option, but it would be rarely used.
+  if (IsDescriptorProto(descriptor)) {
+    return "DescriptorProtoFile";
+  }
   // umbrella_classname can no longer be set using message option.
   std::string proto_file = descriptor->name();
   int lastslash = proto_file.find_last_of("/");

src/google/protobuf/compiler/csharp/csharp_helpers.h

@@ -115,12 +115,7 @@ inline bool IsMapEntryMessage(const Descriptor* descriptor) {
 // for use in the runtime. This is the only type which is allowed to use proto2 syntax,
 // and it generates internal classes.
 inline bool IsDescriptorProto(const FileDescriptor* descriptor) {
-  // TODO: Do this better! (Currently this depends on a hack in generate_protos.sh to rename
-  // the file...)
-  // We need to be able to detect the "normal" name as well, for times that we're just
-  // depending on descriptor.proto instead of generating it.
-  return descriptor->name() == "google/protobuf/descriptor_proto_file.proto"
-      || descriptor->name() == "google/protobuf/descriptor.proto";
+  return descriptor->name() == "google/protobuf/descriptor.proto";
 }
 
 inline bool IsWrapperType(const FieldDescriptor* descriptor) {