Build plugin doesn't discover .proto files as expected

[mylaluna]

I am testing the XCode GRPCProtobufGenerator plugin in my sample project and learning how it can generate stubs for me.

The sample project has following structure:

• TestProtobufGenerator
  • proto
    • post.proto
    • grpc-swift-proto-generator-config.json
  • TestProtobufGenerator
    • ContentView.swift

The grpc-swift-proto-generator-config.json has following content:

{
  "generate": {
    "clients": true,
    "servers": true,
    "messages": true
  },
  "generatedSource": {
    "accessLevelOnImports": false,
    "accessLevel": "internal"
  },
  "protoc": {
    "executablePath": "/opt/homebrew/bin/protoc",
    "importPaths": [
      "proto"
    ]
  }
}

And the post.proto contains:

syntax = "proto3";

message Post {
    int64 id = 1;
    string content = 2;
}

finally the ContentView.swift:

struct ContentView: View {
    var body: some View {
        VStack {
            Text("Post id default: \(Post().id)")
        }
        .padding()
    }
}

This setup gives me a compile error which says "Cannot find 'Post' in scope".
I think this is because the stubs are not generated correctly.

I then tried to use another setup.
Based on the setup above, add both post.proto and grpc-swift-proto-generator-config.json to TestProtobufGenerator target. They will then appear in the Compile Sources of the target.

Change grpc-swift-proto-generator-config.json to following:

{
  "generate": {
    "clients": true,
    "servers": true,
    "messages": true
  },
  "generatedSource": {
    "accessLevelOnImports": false,
    "accessLevel": "internal"
  },
  "protoc": {
    "executablePath": "/opt/homebrew/bin/protoc"
  }
}

Remove the "importPaths" or set it to "", then do a compile. This time the compile will be successful.
I can find both post.grpc.swift and post.pb.swift in the /Users/username/Library/Developer/Xcode/DerivedData/TestProtobufGenerator-id/Build/Intermediates.noindex/BuildToolPluginIntermediates/TestProtobufGenerator.output/TestProtobufGenerator/GRPCProtobufGenerator

However, as a result of adding the post.proto file into the Compile Sources, I get a compile warning:

no rule to process file '/Users/username/Developer/TestProtobufGenerator/proto/post.proto' of type 'sourcecode.protobuf' for architecture 'arm64'

Athough the 2nd setup can generate the stubs I need, I think it is not ideal for two reasons:

1. Adding post.proto to the compile sources is not ideal because it should be the generated stubs rather than the proto files to be added to the compile sources. It produces the warning above.
2. The "importPaths" is somewhat ignored.

My expectation to this plugin is it can use the importPath to discover the proto files in any given directory as long as the directory is referenced in the XCode project, like what the 1st setup was doing.

The fact that documentation mentioned:

The build plugin detects .proto files in the source tree and invokes protoc once for each file (caching results and performing the generation as necessary).

I feel the 1st setup should work.
Is there anything I missed in the 1st setup or I just find a plugin bug?

[glbrntt]

Athough the 2nd setup can generate the stubs I need, I think it is not ideal for two reasons:

1. Adding post.proto to the compile sources is not ideal because it should be the generated stubs rather than the proto files to be added to the compile sources. It produces the warning above.

One way to suppress this is to remove it from "Compile Sources" and add it to "Copy Bundle Resources". This isn't ideal but does suppress the warning.

It's worth filing a Feedback on Xcode about this behaviour.

2. The "importPaths" is somewhat ignored.

My expectation to this plugin is it can use the importPath to discover the proto files in any given directory as long as the directory is referenced in the XCode project, like what the 1st setup was doing.

The import paths option doesn't tell the plugin which files to use as input, it tells protoc where to look for imported .proto files. In your case it's unused because your .proto file doesn't import anything.

The fact that documentation mentioned:

The build plugin detects .proto files in the source tree and invokes protoc once for each file (caching results and performing the generation as necessary).

I feel the 1st setup should work. Is there anything I missed in the 1st setup or I just find a plugin bug?

I think the docs need some additional clarification. It's normally the case that projects are structured by target, so when the plugin is applied to a target all source files in the source tree of the target will be found.

However, this represents an ideal, it's entirely possible for a target to constructed in a different way which isn't something the plugin handles (it wouldn't be reasonable for it to do so). It's also possible for a target to be structured this way and for sources to be excluded such that the plugin doesn't have access to them. As you noted: they must be in compile sources (or resources.)

So I don't consider this to be a bug: it's both a limitation in the way build plugins are integrated with Xcode and a lack of clarity in our documentation.

[mylaluna]

I see — so, as things stand, the plug-in only processes files that are part of the target’s build inputs.

In many real-world setups the .proto files live in a shared schema directory that is version-controlled once and consumed by both the server and every client. The usual goal is to reference that directory from the iOS project (or wrap it in a local Swift package), let the plug-in generate Swift during the build, and avoid having Xcode attempt to compile the raw .proto sources at all.