6. Build Tool Plugins

Build Tool Plugin berjalan selama fase build dan menghasilkan source code atau resources secara otomatis. Output plugin masuk ke derived data, bukan di-commit ke repo.

Dua Jenis Build Tool Plugin

Prebuild Plugin: Berjalan sebelum kompilasi, output bisa berupa source files atau resources
Build Command Plugin: Berjalan sesuai dependency rule (hanya jika input berubah)

Contoh: Protobuf Code Generation Plugin

swift
// Package.swift — definisi plugin package
import PackageDescription

let package = Package(
    name: "ProtoPlugin",
    products: [
        .plugin(name: "ProtobufGeneratorPlugin", targets: ["ProtobufGeneratorPlugin"])
    ],
    dependencies: [
        .package(url: "https://github.com/grpc/grpc-swift", from: "1.0.0")
    ],
    targets: [
        .plugin(
            name: "ProtobufGeneratorPlugin",
            capability: .buildTool(),  // atau .command(intent:)
            dependencies: [
                .product(name: "protoc-gen-swift", package: "grpc-swift")
            ]
        )
    ]
)

swift
// Sources/ProtobufGeneratorPlugin/ProtobufGeneratorPlugin.swift
import PackagePlugin
import Foundation

@main
struct ProtobufGeneratorPlugin: BuildToolPlugin {
    func createBuildCommands(context: PluginContext, target: Target) async throws -> [Command] {
        // Pastikan executable tersedia
        let protoc = try context.tool(named: "protoc")
        let protocGenSwift = try context.tool(named: "protoc-gen-swift")
        
        guard let sourceTarget = target as? SourceModuleTarget else {
            return []
        }
        
        // Cari semua file .proto di target
        let protoFiles = sourceTarget.sourceFiles(withSuffix: "proto").map(\.path)
        
        guard !protoFiles.isEmpty else { return [] }
        
        // Output directory: derived data folder
        let outputDir = context.pluginWorkDirectory.appending("Generated")
        
        // Satu command per file .proto
        return protoFiles.map { protoFile in
            Command.buildCommand(
                displayName: "Generating Swift from \(protoFile.lastComponent)",
                executable: protoc.path,
                arguments: [
                    "--swift_out=\(outputDir)",
                    "--plugin=protoc-gen-swift=\(protocGenSwift.path)",
                    "--proto_path=\(protoFile.removingLastComponent())",
                    protoFile.string
                ],
                inputFiles: [protoFile],
                outputFiles: [
                    outputDir.appending("\(protoFile.stem).pb.swift")
                ]
            )
        }
    }
}

// Untuk Xcode (XcodeBuildToolPlugin protocol)
#if canImport(XcodeProjectPlugin)
import XcodeProjectPlugin

extension ProtobufGeneratorPlugin: XcodeBuildToolPlugin {
    func createBuildCommands(context: XcodePluginContext, target: XcodeTarget) throws -> [Command] {
        let protoFiles = target.inputFiles
            .filter { $0.path.extension == "proto" }
            .map(\.path)
        
        guard !protoFiles.isEmpty else { return [] }
        
        let protoc = try context.tool(named: "protoc")
        let protocGenSwift = try context.tool(named: "protoc-gen-swift")
        let outputDir = context.pluginWorkDirectory.appending("Generated")
        
        return protoFiles.map { protoFile in
            Command.buildCommand(
                displayName: "Generating Swift from \(protoFile.lastComponent)",
                executable: protoc.path,
                arguments: [
                    "--swift_out=\(outputDir)",
                    "--plugin=protoc-gen-swift=\(protocGenSwift.path)",
                    protoFile.string
                ],
                inputFiles: [protoFile],
                outputFiles: [outputDir.appending("\(protoFile.stem).pb.swift")]
            )
        }
    }
}
#endif

swift
// Package.swift — konsumen plugin
let package = Package(
    name: "MyApp",
    dependencies: [
        .package(path: "../ProtoPlugin"),
        .package(url: "https://github.com/grpc/grpc-swift", from: "1.0.0")
    ],
    targets: [
        .target(
            name: "MyApp",
            dependencies: [
                .product(name: "GRPC", package: "grpc-swift")
            ],
            plugins: [
                .plugin(name: "ProtobufGeneratorPlugin", package: "ProtoPlugin")
            ]
        )
    ]
)