compile-proto-file doesn't recognize "extend"

[ethercrow]

I've been trying to use the LightStep grpc protocol from Haskell, their IDL file depends on this one:

// Copyright (c) 2015, Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

package google.api;

import "google/api/http.proto";
import "google/protobuf/descriptor.proto";

option go_package = "google.golang.org/genproto/googleapis/api/annotations;annotations";
option java_multiple_files = true;
option java_outer_classname = "AnnotationsProto";
option java_package = "com.google.api";
option objc_class_prefix = "GAPI";

extend google.protobuf.MethodOptions {
  // See `HttpRule`.
  HttpRule http = 72295728;
}

This is what I get:

$ stack exec -- compile-proto-file --proto google/api/annotations.proto --out blah
Error: failed to compile "google/api/annotations.proto":

CompileParseError "/Users/ethercrow/src/lightstep/google/api/annotations.proto" (line 28, column 1):
unexpected "x"
expecting "enum"

I tried to grep the code and issues of this proto3-suite repository for extend with no success, so maybe nobody just needed it before and it wasn't implemented?

[intractable]

@ethercrow That's correct; it was never implemented and the parser would need to be extended (and then some, see below).

It's been quite some time since I've looked at it, but IIRC: we can't parse google/protobuf/descriptor.proto as it's for proto2, so we would need the ability to support a FileDescriptorSet representation of it that was generated by a proto2 parser.

I believe a complete solution for supporting FileDescriptorSet and extend would entail replacing compile-proto-file with a proper protoc plugin, because then we could rely on the protoc parser instead of our own.