Add option to set custom proto path

[madsodgaard]

Allows the developer to supply a custom directory that will be used as the base of the protofiles.

{
    "invocations": [
        {
            "protoFiles": [
                "file1.proto",
                "file2.proto",
            ],
            "visibility": "public",
            "protoPath": "proto_repo_submodule/protos"
        }
    ]
}

This is useful if you are storing protofiles inside a Git repo and adding that as a submodule to other repos. Giving you a directory structure like:

MySwiftApp/
  - Sources
    - MyAppTarget
      - proto_repo_submodule
        - protos
          - file1.proto
          - file2.proto

and any proto files will be importing other proto files relative to that "protos" directory:

such as in file1.proto

import "file2.proto"

[FranzBusch]

Thanks for opening this PR. Just for my understanding this is a convenience and you could achieve the same with the current options by just passing the full path in the protoFiles option right?

[madsodgaard]

@FranzBusch Unfortunately not. The issue is when the protofiles use import. Any import statements will look for files relative to the proto-path passed to protoc. So If I pass:

{
    "invocations": [
        {
            "protoFiles": [
                "proto_repo_submodule/protos/file1.proto",
                "proto_repo_submodule/protos/file2.proto",
            ],
            "visibility": "public"
        }
    ]
}

and file1.proto, does import "file2.proto2 (which is the correct thing to do), that won't work. Because we just pass MyLibrary/Sources as the protopath.

[FranzBusch]

This LGTM! @glbrntt can you check if that makes sense for the gRPC plugin as well?

[glbrntt]

This should likely be an array rather than a String as you can specify -I/--proto_path multiple times to protoc.

Given the example in the PR description it's not hard to imagine multiple git submodules being added.