Show files generated by build plugins under Target in Project Panel

assets/test/targets/Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version: 5.6
+// swift-tools-version: 5.9
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
@@ -25,7 +25,10 @@ let package = Package(
     ],
     targets: [
         .target(
-            name: "LibraryTarget"
+            name: "LibraryTarget",
+            plugins: [
+                .plugin(name: "BuildToolPlugin")
+            ]
         ),
         .executableTarget(
             name: "ExecutableTarget"
@@ -36,6 +39,11 @@ let package = Package(
                 intent: .custom(verb: "testing", description: "A plugin for testing plugins")
             )
         ),
+        .plugin(
+            name: "BuildToolPlugin",
+            capability: .buildTool(),
+            dependencies: ["ExecutableTarget"]
+        ),
         .testTarget(
             name: "TargetsTests",
             dependencies: ["LibraryTarget"]

assets/test/targets/Plugins/BuildToolPlugin/BuildToolPlugin.swift

@@ -0,0 +1,49 @@
+import PackagePlugin
+import Foundation
+
+@main
+struct SimpleBuildToolPlugin: BuildToolPlugin {
+    func createBuildCommands(context: PluginContext, target: Target) async throws -> [Command] {
+        guard let sourceFiles = target.sourceModule?.sourceFiles else { return [] }
+
+        // Build tool plugins are not being called on Windows with Swift < 6.0.
+        #if os(Windows) && !compiler(>=6.0)
+        return []
+        #endif
+
+        let generatorTool = try context.tool(named: "ExecutableTarget")
+
+        // Construct a build command for each source file with a particular suffix.
+        return sourceFiles.map(\.path).compactMap {
+            createBuildCommand(
+                for: $0,
+                in: context.pluginWorkDirectory,
+                with: generatorTool.path
+            )
+        }
+    }
+
+    /// Calls a build tool that transforms JSON files into Swift files.
+    func createBuildCommand(for inputPath: Path, in outputDirectoryPath: Path, with generatorToolPath: Path) -> Command? {
+        let inputURL = URL(fileURLWithPath: inputPath.string)
+        let outputDirectoryURL = URL(fileURLWithPath: outputDirectoryPath.string)
+
+        // Skip any file that doesn't have the extension we're looking for (replace this with the actual one).
+        guard inputURL.pathExtension == "json" else { return .none }
+
+        // Produces .swift files in the same directory structure as the input JSON files appear in the target.
+        let components = inputURL.absoluteString.split(separator: "LibraryTarget", omittingEmptySubsequences: false).map(String.init)
+        let inputName = inputURL.lastPathComponent
+        let outputDir = outputDirectoryURL.appendingPathComponent(components[1]).deletingLastPathComponent()
+        let outputName = inputURL.deletingPathExtension().lastPathComponent + ".swift"
+        let outputURL = outputDir.appendingPathComponent(outputName)
+
+        return .buildCommand(
+            displayName: "Generating \(outputName) from \(inputName)",
+            executable: generatorToolPath,
+            arguments: ["\(inputPath)", "\(outputURL.path)"],
+            inputFiles: [inputPath],
+            outputFiles: [Path(outputURL.path)]
+        )
+    }
+}

assets/test/targets/Sources/ExecutableTarget/main.swift

@@ -1 +1,39 @@
-print("Executable Target Hello World!")
+import Foundation
+
+@main
+@available(macOS 13.0.0, *)
+struct CodeGenerator {
+    static func main() async throws {
+        // Use swift-argument-parser or just CommandLine, here we just imply that 2 paths are passed in: input and output
+        guard CommandLine.arguments.count == 3 else {
+            throw CodeGeneratorError.invalidArguments
+        }
+        // arguments[0] is the path to this command line tool
+        guard let input = URL(string: "file://\(CommandLine.arguments[1])"), let output = URL(string: "file://\(CommandLine.arguments[2])") else {
+            return
+        }
+        let jsonData = try Data(contentsOf: input)
+        let enumFormat = try JSONDecoder().decode(JSONFormat.self, from: jsonData)
+
+        let code = """
+        enum \(enumFormat.name): CaseIterable {
+        \t\(enumFormat.cases.map({ "case \($0)" }).joined(separator: "\n\t"))
+        }
+        """
+        guard let data = code.data(using: .utf8) else {
+            throw CodeGeneratorError.invalidData
+        }
+        try data.write(to: output, options: .atomic)
+    }
+}
+
+struct JSONFormat: Decodable {
+    let name: String
+    let cases: [String]
+}
+
+@available(macOS 13.00.0, *)
+enum CodeGeneratorError: Error {
+    case invalidArguments
+    case invalidData
+}

assets/test/targets/Sources/LibraryTarget/Bar/Baz.json

@@ -0,0 +1,8 @@
+{
+    "name": "Baz",
+    "cases": [
+        "bar",
+        "baz",
+        "bbb"
+    ]
+}

assets/test/targets/Sources/LibraryTarget/Foo.json

@@ -0,0 +1,8 @@
+{
+    "name": "Foo",
+    "cases": [
+        "bar",
+        "baz",
+        "qux"
+    ]
+}