[xcodegen] Add support for new 'Runtimes' build

Generate a new 'SwiftRuntimes' xcodeproj if a build directory
for 'Runtimes' is specified with `--runtimes-build-dir`, along with a
combined 'Swift+Runtimes' workspace.

Author: hamishknight

utils/swift-xcodegen/README.md

@@ -105,6 +105,14 @@ PROJECT CONFIGURATION:
                           unfortunately means some Clang targes such as 'lib/Basic' and 'stdlib'
                           cannot currently use buildable folders. (default: --buildable-folders)
 
+  --runtimes-build-dir <runtimes-build-dir>
+                          Experimental: The path to a build directory for the new 'Runtimes/'
+                          stdlib CMake build. This creates a separate 'SwiftRuntimes' project, along
+                          with a 'Swift+Runtimes' workspace.
+
+                          Note: This requires passing '-DCMAKE_EXPORT_COMPILE_COMMANDS=YES' to
+                          CMake.
+
 MISC:
   --project-root-dir <project-root-dir>
                           The project root directory, which is the parent directory of the Swift repo.

utils/swift-xcodegen/Sources/SwiftXcodeGen/Ninja/NinjaBuildDir.swift

@@ -13,22 +13,30 @@
 public final class NinjaBuildDir: Sendable {
   public let path: AbsolutePath
   public let projectRootDir: AbsolutePath
-  public let tripleSuffix: String
+  private let _tripleSuffix: Result<String, Error>
 
   private let repoBuildDirs = MutexBox<[Repo: RepoBuildDir]>()
 
   private static func detectTripleSuffix(
     buildDir: AbsolutePath
-  ) throws -> String {
-    for dir in try buildDir.getDirContents() {
-      guard buildDir.appending(dir).isDirectory,
-            let triple = dir.fileName.tryDropPrefix("swift-") else {
-        continue
+  ) -> Result<String, Error> {
+    Result {
+      for dir in try buildDir.getDirContents() {
+        guard buildDir.appending(dir).isDirectory,
+              let triple = dir.fileName.tryDropPrefix("swift-") else {
+          continue
+        }
+        return triple
       }
-      return triple
+      let couldBeParent = buildDir.fileName.hasPrefix("swift-")
+      throw XcodeGenError.noSwiftBuildDir(buildDir, couldBeParent: couldBeParent)
+    }
+  }
+
+  public var tripleSuffix: String {
+    get throws {
+      try _tripleSuffix.get()
     }
-    let couldBeParent = buildDir.fileName.hasPrefix("swift-")
-    throw XcodeGenError.noSwiftBuildDir(buildDir, couldBeParent: couldBeParent)
   }
 
   // We can infer the project root from the location of swift-xcodegen itself.
@@ -51,7 +59,7 @@ public final class NinjaBuildDir: Sendable {
       throw XcodeGenError.pathNotFound(path)
     }
     self.path = path
-    self.tripleSuffix = try Self.detectTripleSuffix(buildDir: path)
+    self._tripleSuffix = Self.detectTripleSuffix(buildDir: path)
     self.projectRootDir = try projectRootDir ?? Self.detectProjectRoot()
   }
 

utils/swift-xcodegen/Sources/SwiftXcodeGen/Ninja/RepoBuildDir.swift

@@ -27,9 +27,9 @@ public final class RepoBuildDir: Sendable {
   init(_ repo: Repo, for parent: NinjaBuildDir) throws {
     self.projectRootDir = parent.projectRootDir
     self.repo = repo
-    self.path = parent.path.appending(
-      "\(repo.buildDirPrefix)-\(parent.tripleSuffix)"
-    )
+    self.path = try repo.buildDirPrefix.map { prefix in
+      parent.path.appending("\(prefix)-\(try parent.tripleSuffix)")
+    } ?? parent.path
     self.repoRelativePath = repo.relativePath
     self.repoPath = projectRootDir.appending(repo.relativePath)
     self.repoDirCache = DirectoryCache(root: repoPath)

utils/swift-xcodegen/Sources/SwiftXcodeGen/Repo.swift

@@ -13,22 +13,25 @@
 // TODO: This really ought to be defined in swift-xcodegen
 public enum Repo: CaseIterable, Sendable {
   case swift
+  case swiftRuntimes
   case lldb
   case llvm
   case cmark
 
   public var relativePath: RelativePath {
     switch self {
     case .swift: "swift"
+    case .swiftRuntimes: "swift/Runtimes"
     case .cmark: "cmark"
     case .lldb:  "llvm-project/lldb"
     case .llvm:  "llvm-project"
     }
   }
 
-  public var buildDirPrefix: String {
+  public var buildDirPrefix: String? {
     switch self {
     case .swift: "swift"
+    case .swiftRuntimes: nil
     case .cmark: "cmark"
     case .lldb:  "lldb"
     case .llvm:  "llvm"

utils/swift-xcodegen/Sources/swift-xcodegen/Options.swift

@@ -222,6 +222,19 @@ struct ProjectOptions: ParsableArguments {
   )
   var useBuildableFolders: Bool = true
 
+  @Option(
+    name: .customLong("runtimes-build-dir"),
+    help: """
+      Experimental: The path to a build directory for the new 'Runtimes/'
+      stdlib CMake build. This creates a separate 'SwiftRuntimes' project, along
+      with a 'Swift+Runtimes' workspace.
+      
+      Note: This requires passing '-DCMAKE_EXPORT_COMPILE_COMMANDS=YES' to
+      CMake.
+      """
+  )
+  var runtimesBuildDir: AnyPath?
+
   @Option(help: .hidden)
   var blueFolders: String = ""
 }

utils/swift-xcodegen/Sources/swift-xcodegen/SwiftXcodegen.swift

@@ -167,6 +167,21 @@ struct SwiftXcodegen: AsyncParsableCommand, Sendable {
     return try spec.generateAndWrite(into: outputDir)
   }
 
+  func writeSwiftRuntimesXcodeProject(
+    for ninja: NinjaBuildDir, into outputDir: AbsolutePath
+  ) throws -> GeneratedProject {
+    let buildDir = try ninja.buildDir(for: .swiftRuntimes)
+    var spec = newProjectSpec("SwiftRuntimes", for: buildDir)
+
+    spec.addClangTarget(at: "core", mayHaveUnbuildableFiles: true)
+    spec.addSwiftTargets(below: "core")
+
+    if self.addDocs {
+      spec.addTopLevelDocs()
+    }
+    return try spec.generateAndWrite(into: outputDir)
+  }
+
   @discardableResult
   func writeClangXcodeProject(
     for ninja: NinjaBuildDir, into outputDir: AbsolutePath
@@ -327,6 +342,15 @@ struct SwiftXcodegen: AsyncParsableCommand, Sendable {
     let swiftProj = try await runTask {
       try writeSwiftXcodeProject(for: buildDir, into: outputDir)
     }
+    let runtimesProj = try await runTask { () -> GeneratedProject? in
+      guard let runtimesBuildDir = self.runtimesBuildDir?.absoluteInWorkingDir else {
+        return nil
+      }
+      let buildDir = try NinjaBuildDir(
+        at: runtimesBuildDir, projectRootDir: projectRootDir
+      )
+      return try writeSwiftRuntimesXcodeProject(for: buildDir, into: outputDir)
+    }
     let llvmProj = try await runTask {
       self.addLLVM ? try writeLLVMXcodeProject(for: buildDir, into: outputDir) : nil
     }
@@ -337,7 +361,12 @@ struct SwiftXcodegen: AsyncParsableCommand, Sendable {
       self.addLLDB ? try writeLLDBXcodeProject(for: buildDir, into: outputDir) : nil
     }
 
-    let swiftWorkspace = try await getWorkspace(for: swiftProj.value)
+    var swiftWorkspace = try await getWorkspace(for: swiftProj.value)
+
+    if let runtimesProj = try await runtimesProj.value {
+      swiftWorkspace.addProject(runtimesProj)
+      try swiftWorkspace.write("Swift+Runtimes", into: outputDir)
+    }
 
     if let llvmProj = try await llvmProj.value {
       var swiftLLVMWorkspace = swiftWorkspace