SwiftProtobufPlugin misses protoc binaryTarget dependency

[olegsur]

SwiftProtobufPlugin requires protoc dependency, however this dependency is not set in the Package.swift. It looks like some improvements were implemented in swift 5.6 which "should" make it possible.

[FranzBusch]

That proposal alone is not enough since there wasn't a possibility to vend binary targets as products. However this PR swiftlang/swift-package-manager#5810 added capabilities for this.
In general, we can't vend protoc from the repository since it might be used by other packages which do not require protobuf generation. I would recommend opening an issue over in the protocolbuffers repository where you ask them to add a Package.swift that vends protoc. The protobuf team can then decide if they want to do this. More specifically they can decide if they want to vend a binary artefact or build protoc via SPM.

[olegsur]

It does not look like that protocolbuffers repository should have Package.swift because protoc is not a Swift package. But it would be nice if they add this support. Here the issue.

[FranzBusch]

@olegsur If something is a Swift package or not is not relevant for this. SPM can also build C and C++ targets. An example of this is zstd.

[olegsur]

@FranzBusch You are right, it should be irrelevant if protobuf is a Swift package or not. This is a question about who should be responsible for creating binary build artifact which could be used by SPM. I hope, the protobuf team will accept the feature request.