Implement proposed adjustments to SE-0303 to use @main for plugins

Fixtures/Miscellaneous/AtMainSupport/Sources/SwiftExecMultiFile/NotMain.swift

@@ -1,4 +1,4 @@
-@main 
+@main
 struct MyProgram {
     static func main() {
         print("Hello, Swift.")

Fixtures/Miscellaneous/AtMainSupport/Sources/SwiftExecSingleFile/NotMain.swift

@@ -1,4 +1,4 @@
-@main 
+@main
 struct MyProgram {
     static func main() {
         print("Hello, Swift.")

Fixtures/Miscellaneous/Plugins/ContrivedTestPlugin/Plugins/MyAmbiguouslyNamedCommandPlugin/plugin.swift

@@ -1,26 +1,34 @@
 import PackagePlugin
 
-for inputFile in targetBuildContext.inputFiles.filter({ $0.path.extension == "dat" }) {
-    let inputPath = inputFile.path
-    let outputName = "Ambiguous_" + inputPath.stem + ".swift"
-    let outputPath = targetBuildContext.pluginWorkDirectory.appending(outputName)
-    commandConstructor.addBuildCommand(
-        displayName:
-            "This is a constant name",
-        executable:
-            try targetBuildContext.tool(named: "MySourceGenBuildTool").path,
-        arguments: [
-            "\(inputPath)",
-            "\(outputPath)"
-        ],
-        environment: [
-            "VARIABLE_NAME_PREFIX": "SECOND_PREFIX_"
-        ],
-        inputFiles: [
-            inputPath,
-        ],
-        outputFiles: [
-            outputPath
-        ]
-    )
+@main
+struct MyPlugin: BuildToolPlugin {
+
+    func createBuildCommands(context: TargetBuildContext) throws -> [Command] {
+        var commands: [Command] = []
+        for inputFile in context.inputFiles.filter({ $0.path.extension == "dat" }) {
+            let inputPath = inputFile.path
+            let outputName = "Ambiguous_" + inputPath.stem + ".swift"
+            let outputPath = context.pluginWorkDirectory.appending(outputName)
+            commands.append(.buildCommand(
+                displayName:
+                    "This is a constant name",
+                executable:
+                    try context.tool(named: "MySourceGenBuildTool").path,
+                arguments: [
+                    "\(inputPath)",
+                    "\(outputPath)"
+                ],
+                environment: [
+                    "VARIABLE_NAME_PREFIX": "SECOND_PREFIX_"
+                ],
+                inputFiles: [
+                    inputPath,
+                ],
+                outputFiles: [
+                    outputPath
+                ]
+            ))
+        }
+        return commands
+    }
 }

Fixtures/Miscellaneous/Plugins/ContrivedTestPlugin/Plugins/MySourceGenBuildToolPlugin/plugin.swift

@@ -1,28 +1,34 @@
 import PackagePlugin
 
-print("Hello from the Build Tool Plugin!")
-
-for inputFile in targetBuildContext.inputFiles.filter({ $0.path.extension == "dat" }) {
-    let inputPath = inputFile.path
-    let outputName = inputPath.stem + ".swift"
-    let outputPath = targetBuildContext.pluginWorkDirectory.appending(outputName)
-    commandConstructor.addBuildCommand(
-        displayName:
-            "Generating \(outputName) from \(inputPath.lastComponent)",
-        executable:
-            try targetBuildContext.tool(named: "MySourceGenBuildTool").path,
-        arguments: [
-            "\(inputPath)",
-            "\(outputPath)"
-        ],
-        environment: [
-            "VARIABLE_NAME_PREFIX": "PREFIX_"
-        ],
-        inputFiles: [
-            inputPath,
-        ],
-        outputFiles: [
-            outputPath
-        ]
-    )
+@main
+struct MyPlugin: BuildToolPlugin {
+
+    func createBuildCommands(context: TargetBuildContext) throws -> [Command] {
+        let inputFiles = context.inputFiles.filter({ $0.path.extension == "dat" })
+        return try inputFiles.map {
+            let inputFile = $0
+            let inputPath = inputFile.path
+            let outputName = inputPath.stem + ".swift"
+            let outputPath = context.pluginWorkDirectory.appending(outputName)
+            return .buildCommand(
+                displayName:
+                    "Generating \(outputName) from \(inputPath.lastComponent)",
+                executable:
+                    try context.tool(named: "MySourceGenBuildTool").path,
+                arguments: [
+                    "\(inputPath)",
+                    "\(outputPath)"
+                ],
+                environment: [
+                    "VARIABLE_NAME_PREFIX": "PREFIX_"
+                ],
+                inputFiles: [
+                    inputPath,
+                ],
+                outputFiles: [
+                    outputPath
+                ]
+            )
+        }
+    }
 }

Fixtures/Miscellaneous/Plugins/MyBinaryToolPlugin/Plugins/MySourceGenBuildToolPlugin/plugin.swift

@@ -1,26 +1,34 @@
 import PackagePlugin
-
-print("Hello from the Build Tool Plugin!")
 
-for inputFile in targetBuildContext.inputFiles.filter({ $0.path.extension == "dat" }) {
-    let inputPath = inputFile.path
-    let outputName = inputPath.stem + ".swift"
-    let outputPath = targetBuildContext.pluginWorkDirectory.appending(outputName)
-    commandConstructor.addBuildCommand(
-        displayName:
-            "Generating \(outputName) from \(inputPath.lastComponent)",
-        executable:
-            try targetBuildContext.tool(named: "mytool").path,
-        arguments: [
-            "--verbose",
-            "\(inputPath)",
-            "\(outputPath)"
-        ],
-        inputFiles: [
-            inputPath,
-        ],
-        outputFiles: [
-            outputPath
-        ]
-    )
+@main
+struct MyPlugin: BuildToolPlugin {
+
+    func createBuildCommands(context: TargetBuildContext) throws -> [Command] {
+        print("Hello from the Build Tool Plugin!")
+
+        let inputFiles = context.inputFiles.filter({ $0.path.extension == "dat" })
+        return try inputFiles.map {
+            let inputFile = $0
+            let inputPath = inputFile.path
+            let outputName = inputPath.stem + ".swift"
+            let outputPath = context.pluginWorkDirectory.appending(outputName)
+            return .buildCommand(
+                displayName:
+                    "Generating \(outputName) from \(inputPath.lastComponent)",
+                executable:
+                    try context.tool(named: "mytool").path,
+                arguments: [
+                    "--verbose",
+                    "\(inputPath)",
+                    "\(outputPath)"
+                ],
+                inputFiles: [
+                    inputPath,
+                ],
+                outputFiles: [
+                    outputPath
+                ]
+            )
+        }
+    }
 }

Fixtures/Miscellaneous/Plugins/MySourceGenPlugin/Plugins/MySourceGenBuildToolPlugin/plugin.swift

@@ -1,25 +1,31 @@
 import PackagePlugin
-
-print("Hello from the Build Tool Plugin!")
 
-for inputPath in targetBuildContext.inputFiles.map{ $0.path } {
-    guard inputPath.extension == "dat" else { continue }
-    let outputName = inputPath.stem + ".swift"
-    let outputPath = targetBuildContext.pluginWorkDirectory.appending(outputName)
-    commandConstructor.addBuildCommand(
-        displayName:
-            "Generating \(outputName) from \(inputPath.lastComponent)",
-        executable:
-            try targetBuildContext.tool(named: "MySourceGenBuildTool").path,
-        arguments: [
-            "\(inputPath)",
-            "\(outputPath)"
-        ],
-        inputFiles: [
-            inputPath,
-        ],
-        outputFiles: [
-            outputPath
-        ]
-    )
+@main
+struct MyPlugin: BuildToolPlugin {
+
+    func createBuildCommands(context: TargetBuildContext) throws -> [Command] {
+        print("Hello from the Build Tool Plugin!")
+
+        return try context.inputFiles.map{ $0.path }.compactMap {
+            guard $0.extension == "dat" else { return .none }
+            let outputName = $0.stem + ".swift"
+            let outputPath = context.pluginWorkDirectory.appending(outputName)
+            return .buildCommand(
+                displayName:
+                    "Generating \(outputName) from \($0.lastComponent)",
+                executable:
+                    try context.tool(named: "MySourceGenBuildTool").path,
+                arguments: [
+                    "\($0)",
+                    "\(outputPath)"
+                ],
+                inputFiles: [
+                    $0,
+                ],
+                outputFiles: [
+                    outputPath
+                ]
+            )
+        }
+    }
 }

Fixtures/Miscellaneous/Plugins/MySourceGenPlugin/Plugins/MySourceGenPrebuildPlugin/plugin.swift

@@ -1,20 +1,27 @@
 import PackagePlugin
-
-print("Hello from the Prebuild Plugin!")
 
-let outputPaths: [Path] = targetBuildContext.inputFiles.filter{ $0.path.extension == "dat" }.map { file in
-    targetBuildContext.pluginWorkDirectory.appending(file.path.stem + ".swift")
-}
+@main
+struct MyPlugin: BuildToolPlugin {
+
+    func createBuildCommands(context: TargetBuildContext) throws -> [Command] {
+        print("Hello from the Prebuild Plugin!")
 
-if !outputPaths.isEmpty {
-    commandConstructor.addPrebuildCommand(
-        displayName:
-            "Running prebuild command for target \(targetBuildContext.targetName)",
-        executable:
-            Path("/usr/bin/touch"),
-        arguments: 
-            outputPaths.map{ $0.string },
-        outputFilesDirectory:
-            targetBuildContext.pluginWorkDirectory
-    )
+        let outputPaths: [Path] = context.inputFiles.filter{ $0.path.extension == "dat" }.map { file in
+            context.pluginWorkDirectory.appending(file.path.stem + ".swift")
+        }
+        var commands: [Command] = []
+        if !outputPaths.isEmpty {
+            commands.append(.prebuildCommand(
+                displayName:
+                    "Running prebuild command for target \(context.targetName)",
+                executable:
+                    Path("/usr/bin/touch"),
+                arguments: 
+                    outputPaths.map{ $0.string },
+                outputFilesDirectory:
+                    context.pluginWorkDirectory
+            ))
+        }
+        return commands
+    }
 }

Fixtures/Miscellaneous/Plugins/SandboxTesterPlugin/Plugins/MySourceGenBuildToolPlugin/plugin.swift

@@ -1,23 +1,31 @@
 import PackagePlugin
 import Foundation
-
-// Check that we can write to the output directory.
-let allowedOutputPath = targetBuildContext.pluginWorkDirectory.appending("Foo")
-if mkdir(allowedOutputPath.string, 0o777) != 0 {
-     throw StringError("unexpectedly could not write to '\(allowedOutputPath)': \(String(utf8String: strerror(errno)))")
-}
 
-// Check that we cannot write to the source directory.
-let disallowedOutputPath = targetBuildContext.targetDirectory.appending("Bar")
-if mkdir(disallowedOutputPath.string, 0o777) == 0 {
-     throw StringError("unexpectedly could write to '\(disallowedOutputPath)'")
-}
+@main
+struct MyPlugin: BuildToolPlugin {
+
+    func createBuildCommands(context: TargetBuildContext) throws -> [Command] {
+
+        // Check that we can write to the output directory.
+        let allowedOutputPath = context.pluginWorkDirectory.appending("Foo")
+        if mkdir(allowedOutputPath.string, 0o777) != 0 {
+             throw StringError("unexpectedly could not write to '\(allowedOutputPath)': \(String(utf8String: strerror(errno)))")
+        }
 
+        // Check that we cannot write to the source directory.
+        let disallowedOutputPath = context.targetDirectory.appending("Bar")
+        if mkdir(disallowedOutputPath.string, 0o777) == 0 {
+             throw StringError("unexpectedly could write to '\(disallowedOutputPath)'")
+        }
+
+        return []
+    }
 
-struct StringError: Error, CustomStringConvertible {
-    var error: String
-    init(_ error: String) {
-        self.error = error
+    struct StringError: Error, CustomStringConvertible {
+        var error: String
+        init(_ error: String) {
+            self.error = error
+        }
+        var description: String { error }
     }
-    var description: String { error }
 }

Sources/PackagePlugin/CMakeLists.txt

@@ -7,13 +7,13 @@
 # See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 
 add_library(PackagePlugin
-  PublicAPI/CommandConstructor.swift
-  PublicAPI/DiagnosticsEmitter.swift
+  PublicAPI/Command.swift
+  PublicAPI/Context.swift
+  PublicAPI/Diagnostics.swift
   PublicAPI/FileList.swift
-  PublicAPI/Globals.swift
   PublicAPI/Path.swift
-  PublicAPI/TargetBuildContext.swift
-  ImplementationDetails.swift)
+  PublicAPI/Protocols.swift
+  Implementation.swift)
 
 target_compile_options(PackagePlugin PUBLIC
   $<$<COMPILE_LANGUAGE:Swift>:-package-description-version$<SEMICOLON>999.0>)