[swiftpm] For development, build a local copy of PackageDescription

Package.swift

@@ -83,9 +83,14 @@ let package = Package(
           "BuildServerProtocol",
           "LanguageServerProtocol",
           "SKCore",
-          .product(name: "SwiftPM-auto", package: "SwiftPM")
-        ],
-        exclude: ["CMakeLists.txt"]),
+          .product(name: "SwiftPM-auto", package: "SwiftPM"),
+        ] + (useLocalPackageDescriptionModule() ? [
+          .product(name: "PackageDescription", package: "SwiftPM"),
+        ] : []),
+        exclude: ["CMakeLists.txt"],
+        swiftSettings: useLocalPackageDescriptionModule() ? [
+          .define("USE_LOCAL_PACKAGE_DESCRIPTION_MODULE")
+        ] : []),
 
       .testTarget(
         name: "SKSwiftPMWorkspaceTests",
@@ -248,3 +253,11 @@ if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
     .package(path: "../swift-argument-parser")
   ]
 }
+
+func useLocalPackageDescriptionModule() -> Bool {
+  // By default, create a local PackageDescription module to ensure it stays
+  // in sync with libSwiftPM during development. To install sourcekit-lsp as
+  // part of the toolchain we use the toolchain's own PackageDescription, and
+  // rely on the whole toolchain being built from the same swiftpm sources.
+  return ProcessInfo.processInfo.environment["SWIFTCI_USE_TOOLCHAIN_PACKAGE_DESCRIPTION"] == nil
+}

Sources/SKSwiftPMWorkspace/SwiftPMWorkspace.swift

@@ -25,7 +25,7 @@ import SKCore
 import SKSupport
 import Workspace
 import Dispatch
-import struct Foundation.URL
+import Foundation
 
 /// Swift Package Manager build system and workspace support.
 ///
@@ -84,6 +84,7 @@ public final class SwiftPMWorkspace {
 
     let destination = try Destination.hostDestination(destinationToolchainBinDir)
     let toolchain = try UserToolchain(destination: destination)
+    let manifestResources = manifestResources(for: toolchain)
 
     let buildPath: AbsolutePath = buildSetup.path ?? packageRoot.appending(component: ".build")
 
@@ -93,7 +94,7 @@ public final class SwiftPMWorkspace {
         dataPath: buildPath,
         editablesPath: packageRoot.appending(component: "Packages"),
         pinsFile: packageRoot.appending(component: "Package.resolved"),
-        manifestLoader: ManifestLoader(manifestResources: toolchain.manifestResources, cacheDir: buildPath),
+        manifestLoader: ManifestLoader(manifestResources: manifestResources, cacheDir: buildPath),
         config: workspaceConfiguration,
         fileSystem: fileSystem,
         skipUpdate: true)
@@ -122,7 +123,7 @@ public final class SwiftPMWorkspace {
   /// Creates a build system using the Swift Package Manager, if this workspace is a package.
   ///
   /// - Returns: nil if `workspacePath` is not part of a package or there is an error.
-  public convenience init?(url: URL,
+  public convenience init?(url: Foundation.URL,
                            toolchainRegistry: ToolchainRegistry,
                            buildSetup: BuildSetup)
   {
@@ -454,3 +455,37 @@ extension TSCBasic.Diagnostic.Behavior {
     }
   }
 }
+
+private func manifestResources(for toolchain: UserToolchain) -> ManifestResourceProvider {
+  #if USE_LOCAL_PACKAGE_DESCRIPTION_MODULE
+  var buildURL = Bundle(for: SwiftPMWorkspace.self).bundleURL
+  if buildURL.pathExtension == "xctest" {
+    // If we are statically linked into a test bundle, look in the parent.
+    buildURL.deleteLastPathComponent()
+  }
+  // Look for a local copy of PackageDescription -- either as a bare module, or
+  // a framework when building with Xcode. If we find a local PackageDescription
+  // module, override the manifest resources `binDir` so that it will be used
+  // instead of the toolchain's own manifest resources.
+  let fileManager = FileManager.default
+  let bareModule = buildURL
+    .appendingPathComponent("PackageDescription.swiftmodule")
+  let frameworkModule = buildURL
+    .appendingPathComponent("PackageFrameworks")
+    .appendingPathComponent("PackageDescription.framework")
+  if fileManager.fileExists(atPath: bareModule.path) || fileManager.fileExists(atPath: frameworkModule.path) {
+    let manifestResources = toolchain.manifestResources
+    return UserManifestResources(
+      swiftCompiler: manifestResources.swiftCompiler,
+      swiftCompilerFlags: manifestResources.swiftCompilerFlags,
+      libDir: manifestResources.libDir,
+      sdkRoot: manifestResources.sdkRoot,
+      xctestLocation: manifestResources.xctestLocation,
+      binDir: AbsolutePath(buildURL.path))
+  } else {
+    log("requested USE_LOCAL_PACKAGE_DESCRIPTION_MODULE but did not find PackageDescription in \(buildURL); falling back to toolchain resources", level: .error)
+  }
+  #endif
+
+  return toolchain.manifestResources
+}

Utilities/build-script-helper.py

@@ -97,6 +97,9 @@ def handle_invocation(swift_exec, args):
   if not args.no_local_deps:
     env['SWIFTCI_USE_LOCAL_DEPS'] = "1"
 
+  # Always use the toolchain's package description module.
+  env['SWIFTCI_USE_TOOLCHAIN_PACKAGE_DESCRIPTION'] = "1"
+
   if args.ninja_bin:
     env['NINJA_BIN'] = args.ninja_bin