When using protoc with syntax = "proto3" I'm getting the following error:

Unrecognized syntax identifier "proto3". This parser only recognizes "proto2".

Here is the output of protoc --version:

libprotoc 2.6.1

I've tried installing protobuf using brew, from the downloadable tarball, and also by downloading the 2.6.1 source from github. I've tried removing all other protobuf libraries on my system.

I notice the following lines of code in https://github.com/google/protobuf/blob/v2.6.1/src/google/protobuf/compiler/parser.cc

if (syntax != "proto2" && !stop_after_syntax_identifier_) {
AddError(syntax_token.line, syntax_token.column,
"Unrecognized syntax identifier "" + syntax + "". This parser "
"only recognizes "proto2".");
return false;
}