Pass the correct toolchain path to SwiftBuild on Windows and FreeBSD

Amendment to #8696 which computes the correct path on Windows and FreeBSD, which use different install layouts from the other platforms.

Author: jakepetroules

Sources/Basics/CMakeLists.txt

@@ -60,6 +60,7 @@ add_library(Basics
   Netrc.swift
   Observability.swift
   OSSignpost.swift
+  Process.swift
   ProgressAnimation/NinjaProgressAnimation.swift
   ProgressAnimation/PercentProgressAnimation.swift
   ProgressAnimation/ProgressAnimationProtocol.swift

Sources/_InternalTestSupport/Process.swift renamed to Sources/Basics/Process.swift

@@ -15,19 +15,24 @@ public enum OperatingSystem: Hashable, Sendable {
     case windows
     case linux
     case android
+    case freebsd
     case unknown
 }
 
 extension ProcessInfo {
-    #if os(macOS)
-    public static let hostOperatingSystem = OperatingSystem.macOS
-    #elseif os(Linux)
-    public static let hostOperatingSystem = OperatingSystem.linux
-    #elseif os(Windows)
-    public static let hostOperatingSystem = OperatingSystem.windows
-    #else
-    public static let hostOperatingSystem = OperatingSystem.unknown
-    #endif
+    public static var hostOperatingSystem: OperatingSystem {
+        #if os(macOS)
+        .macOS
+        #elseif os(Linux)
+        .linux
+        #elseif os(Windows)
+        .windows
+        #elseif os(FreeBSD)
+        .freebsd
+        #else
+        .unknown
+        #endif
+    }
 
     #if os(Windows)
     public static let EOL = "\r\n"

Sources/PackageModel/Toolchain.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 import Basics
+import Foundation
 
 public protocol Toolchain {
     /// Path of the librarian.
@@ -88,12 +89,33 @@ extension Toolchain {
         }
     }
 
+    /// Base toolchain path that's given to Swift Build to initialize its core.
     public var toolchainDir: AbsolutePath {
         get throws {
-            try resolveSymlinks(swiftCompilerPath)
-                .parentDirectory // bin
-                .parentDirectory // usr
-                .parentDirectory // <toolchain>
+            let compilerPath = try resolveSymlinks(swiftCompilerPath)
+            let os = ProcessInfo.hostOperatingSystem
+            switch os {
+            case .windows:
+                return compilerPath
+                    .parentDirectory // bin
+                    .parentDirectory // usr
+                    .parentDirectory // <version>
+                    .parentDirectory // Toolchains
+                    .parentDirectory // <toolchain>
+            case .macOS, .linux, .android:
+                return compilerPath
+                    .parentDirectory // bin
+                    .parentDirectory // usr
+                    .parentDirectory // <toolchain>
+            case .freebsd:
+                return compilerPath
+                    .parentDirectory // bin
+                    .parentDirectory // local
+                    .parentDirectory // usr
+                    .parentDirectory // <toolchain>
+            case .unknown:
+                throw UnknownToolchainLayout(os: os)
+            }
         }
     }
 
@@ -128,3 +150,10 @@ extension Toolchain {
         try AbsolutePath(validating: "../../lib", relativeTo: resolveSymlinks(swiftCompilerPath))
     }
 }
+
+struct UnknownToolchainLayout: Error, CustomStringConvertible {
+    let os: OperatingSystem
+    var description: String {
+        "Unknown toolchain layout for host operating system: \(os)"
+    }
+}

Sources/_InternalTestSupport/SkippedTestSupport.swift

@@ -11,6 +11,7 @@
 
 import class Foundation.FileManager
 import class Foundation.ProcessInfo
+import Basics
 import Testing
 
 extension Trait where Self == Testing.ConditionTrait {