"extend" is not allowed in proto3 spec, but is used in tests

[stepancheg]

Spec 3 doesn't mention extend unlike Spec 2.

However extend with syntax = "proto3" is used in protobuf tests.

[TeBoring]

Only MessageOption, which is internal. Don't use it by yourself.

[stepancheg]

@TeBoring unfortunately protobuf compiler protoc accepts this option. And I'm writing Rust implementation of protobuf, and my implementation should be compatible with protoc.

If this option is not meant to be used outside of Google, then public version of protoc compiler should probably reject it.

[stepancheg]

%%% cat ./aaa.proto
syntax = "proto3";

import "google/protobuf/descriptor.proto";

message TestImportDescriptorProto {
  extend google.protobuf.MethodOptions {
    int32 a = 72295727;
  }
}

extend google.protobuf.MethodOptions {
  int32 a = 72295728;
}
%%% protoc --cpp_out=. ./aaa.proto
%%% protoc --version
libprotoc 3.5.0

[TeBoring]

@anandolee, we can still define custom option in proto3, right?

[xfxyjwf]

In proto3, custom options are allowed, i.e., users can use "extend" keyword to define their own extensions to proto descriptor options. The spec is missing stuff because it was created after protoc, i.e., it's introduced to describe what protoc does, rather than defining what protoc does. If you are implementing protobuf support in a new language it's better to follow what protoc accepts instead of what the spec doc says.

[subfuzion]

I know the issue is closed, but can the misleading title (which shows up in searches) be fixed? I believe now is supposed to be not.

[fowles]

Fixed! (I hate that typo and am amazed how often I make it)