Allow passing extra arguments to plugin compilation

CHANGELOG.md

@@ -3,6 +3,10 @@ Note: This is in reverse chronological order, so newer entries are added to the
 Swift Next
 -----------
 
+* [#5966]
+
+  Plugin compilation can be influenced by using `-Xbuild-tools-swiftc` arguments in the SwiftPM command line. This is similar to the existing mechanism for influencing the manifest compilation using `-Xmanifest` arguments. Manifest compilation will also be influenced by `-Xbuild-tools-swiftc`, but only if no other `-Xmanifest` arguments are provided. Using `-Xmanifest` will show a deprecation message. `-Xmanifest` will be removed in the future.
+
 * [#5728]
 
   In packages that specify resources using a future tools version, the generated resource bundle accessor will import `Foundation.Bundle` for its own implementation only. _Clients_ of such packages therefore no longer silently import `Foundation`, preventing inadvertent use of Foundation extensions to standard library APIs, which helps to avoid unexpected code size increases.
@@ -318,6 +322,7 @@ Swift 3.0
 [#5874]: https://github.com/apple/swift-package-manager/pull/5874
 [#5949]: https://github.com/apple/swift-package-manager/pull/5949
 [#5892]: https://github.com/apple/swift-package-manager/pull/5892
+[#5966]: https://github.com/apple/swift-package-manager/pull/5966
 [#6060]: https://github.com/apple/swift-package-manager/pull/6060
 [#6067]: https://github.com/apple/swift-package-manager/pull/6067
 [#6114]: https://github.com/apple/swift-package-manager/pull/6114

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

@@ -2,7 +2,12 @@ import PackagePlugin
 
 @main
 struct MyPlugin: BuildToolPlugin {
-
+    #if USE_CREATE
+    let verb = "Creating"
+    #else
+    let verb = "Generating"
+    #endif
+
     func createBuildCommands(context: PluginContext, target: Target) throws -> [Command] {
         print("Hello from the Build Tool Plugin!")
         guard let target = target as? SourceModuleTarget else { return [] }
@@ -12,7 +17,7 @@ struct MyPlugin: BuildToolPlugin {
             let outputPath = context.pluginWorkDirectory.appending(outputName)
             return .buildCommand(
                 displayName:
-                    "Generating \(outputName) from \($0.lastComponent)",
+                    "\(verb) \(outputName) from \($0.lastComponent)",
                 executable:
                     try context.tool(named: "MySourceGenBuildTool").path,
                 arguments: [

Sources/CoreCommands/Options.swift

@@ -326,15 +326,35 @@ public struct BuildOptions: ParsableArguments {
     )
     public var xcbuildFlags: [String] = []
 
+    @Option(
+        name: .customLong("Xbuild-tools-swiftc", withSingleDash: true),
+        parsing: .unconditionalSingleValue,
+        help: ArgumentHelp(
+            "Pass flag to Swift compiler invocations for build-time executables (manifest and plugins)",
+            visibility: .hidden
+        )
+    )
+    public var _buildToolsSwiftCFlags: [String] = []
+
     @Option(
         name: .customLong("Xmanifest", withSingleDash: true),
         parsing: .unconditionalSingleValue,
         help: ArgumentHelp(
-            "Pass flag to the manifest build invocation",
+            "Pass flag to the manifest build invocation. Deprecated: use '-Xbuild-tools-swiftc' instead",
             visibility: .hidden
         )
     )
-    var manifestFlags: [String] = []
+    public var _deprecated_manifestFlags: [String] = []
+
+    var manifestFlags: [String] {
+        self._deprecated_manifestFlags.isEmpty ?
+            self._buildToolsSwiftCFlags :
+            self._deprecated_manifestFlags
+    }
+
+    var pluginSwiftCFlags: [String] {
+        self._buildToolsSwiftCFlags
+    }
 
     public var buildFlags: BuildFlags {
         BuildFlags(

Sources/CoreCommands/SwiftTool.swift

@@ -423,6 +423,10 @@ public final class SwiftTool {
         if let _ = options.security.netrcFilePath, options.security.netrc == false {
             observabilityScope.emit(.mutuallyExclusiveArgumentsError(arguments: ["--disable-netrc", "--netrc-file"]))
         }
+
+        if !options.build._deprecated_manifestFlags.isEmpty {
+            observabilityScope.emit(warning: "'-Xmanifest' option is deprecated; use '-Xbuild-tools-swiftc' instead")
+        }
     }
 
     func waitForObservabilityEvents(timeout: DispatchTime) {
@@ -620,6 +624,7 @@ public final class SwiftTool {
             fileSystem: self.fileSystem,
             cacheDir: cacheDir,
             toolchain: self.getHostToolchain(),
+            extraPluginSwiftCFlags: self.options.build.pluginSwiftCFlags,
             enableSandbox: !self.shouldDisableSandbox,
             verboseOutput: self.logLevel <= .info
         )

Sources/Workspace/DefaultPluginScriptRunner.swift

@@ -24,16 +24,25 @@ public struct DefaultPluginScriptRunner: PluginScriptRunner, Cancellable {
     private let fileSystem: FileSystem
     private let cacheDir: AbsolutePath
     private let toolchain: UserToolchain
+    private let extraPluginSwiftCFlags: [String]
     private let enableSandbox: Bool
     private let cancellator: Cancellator
     private let verboseOutput: Bool
 
     private let sdkRootCache = ThreadSafeBox<AbsolutePath>()
 
-    public init(fileSystem: FileSystem, cacheDir: AbsolutePath, toolchain: UserToolchain, enableSandbox: Bool = true, verboseOutput: Bool = false) {
+    public init(
+        fileSystem: FileSystem,
+        cacheDir: AbsolutePath,
+        toolchain: UserToolchain,
+        extraPluginSwiftCFlags: [String] = [],
+        enableSandbox: Bool = true,
+        verboseOutput: Bool = false
+    ) {
         self.fileSystem = fileSystem
         self.cacheDir = cacheDir
         self.toolchain = toolchain
+        self.extraPluginSwiftCFlags = extraPluginSwiftCFlags
         self.enableSandbox = enableSandbox
         self.cancellator = Cancellator(observabilityScope: .none)
         self.verboseOutput = verboseOutput
@@ -209,6 +218,9 @@ public struct DefaultPluginScriptRunner: PluginScriptRunner, Cancellable {
         // Finally add the output path of the compiled executable.
         commandLine += ["-o", execFilePath.pathString]
 
+        // Add any extra flags passed for the host in the command line
+        commandLine += self.extraPluginSwiftCFlags
+
         if (verboseOutput) {
             commandLine.append("-v")
         }

Tests/FunctionalTests/PluginTests.swift

@@ -1009,4 +1009,25 @@ class PluginTests: XCTestCase {
             XCTAssert(stdout.contains("Build complete!"), "stdout:\n\(stdout)")
         }
     }
+
+    func testPluginCanBeAffectedByXBuildToolsParameters() throws {
+        // Only run the test if the environment in which we're running actually supports Swift concurrency (which the
+        // plugin APIs require).
+        try XCTSkipIf(
+            !UserToolchain.default.supportsSwiftConcurrency(),
+            "skipping because test environment doesn't support concurrency"
+        )
+
+        try fixture(name: "Miscellaneous/Plugins") { fixturePath in
+            let (stdout, _) = try executeSwiftBuild(
+                fixturePath.appending(component: "MySourceGenPlugin"),
+                configuration: .Debug,
+                extraArgs: ["--product", "MyLocalTool", "-Xbuild-tools-swiftc", "-DUSE_CREATING"]
+            )
+            XCTAssert(stdout.contains("Linking MySourceGenBuildTool"), "stdout:\n\(stdout)")
+            XCTAssert(stdout.contains("Creating foo.swift from foo.dat"), "stdout:\n\(stdout)")
+            XCTAssert(stdout.contains("Linking MyLocalTool"), "stdout:\n\(stdout)")
+            XCTAssert(stdout.contains("Build complete!"), "stdout:\n\(stdout)")
+        }
+    }
 }