On Darwin, allow XCTest to be missing if we're only building swift-te…

…sting tests.

This PR removes the constraint on Darwin that XCTest.framework must be present
in order to build tests using swift-testing. On Darwin, XCTest is included as a
framework inside Xcode, but if a developer installs the Xcode Command Line Tools
instead of the full IDE, XCTest is not included. They then get a diagnostic of
the form:

> error: XCTest not available: terminated(1): /usr/bin/xcrun --sdk macosx --show-sdk-platform-path output:
>    xcrun: error: unable to lookup item 'PlatformPath' from command line tools installation
>    xcrun: error: unable to lookup item 'PlatformPath' in SDK '/Library/Developer/CommandLineTools/SDKs/MacOSX14.0.sdk'

Which is a poor experience if they aren't even using XCTest.

This change, as a (positive) side effect, suppresses the same diagnostic when
running commands that are not usually dependent on the presence of XCTest such
as `swift build`.

Note that swift-corelibs-xctest is not supported on Darwin, so installing the
Xcode Command Line Tools and adding an explicit dependency on
swift-corelibs-xctest will not produce a functional test target bundle.
Supporting swift-corelibs-xctest on Darwin is a potential future direction.

Automated testing for this change is difficult because it relies on a build
environment that is not supported in CI (namely the presence of the CL tools but
not Xcode nor XCTest.framework.) I have manually tested the change against
swift-testing's own test target.

A separate PR will be necessary in swift-testing to remove some remaining XCTest
dependencies. Those changes are not covered by this PR.

Resolves rdar://125372431.

Sources/Commands/SwiftTestCommand.swift

@@ -40,7 +40,7 @@ private enum TestError: Swift.Error {
  case testProductNotFound(productName: String)
  case productIsNotTest(productName: String)
  case multipleTestProducts([String])
- case xctestNotAvailable
+ case xctestNotAvailable(reason: String? = nil)
 }
 
 extension TestError: CustomStringConvertible {
@@ -57,8 +57,12 @@ extension TestError: CustomStringConvertible {
  return "invalid list test JSON structure, produced by \(context)\(underlying)"
  case .multipleTestProducts(let products):
  return "found multiple test products: \(products.joined(separator: ", ")); use --test-product to select one"
- case .xctestNotAvailable:
- return "XCTest not available"
+ case let .xctestNotAvailable(reason):
+ if let reason {
+ return "XCTest not available: \(reason)"
+ } else {
+ return "XCTest not available"
+ }
  }
  }
 }
@@ -203,9 +207,10 @@ package struct SwiftTestCommand: AsyncSwiftCommand {
  private func xctestRun(_ swiftCommandState: SwiftCommandState) async throws {
  // validate XCTest available on darwin based systems
  let toolchain = try swiftCommandState.getTargetToolchain()
- let isHostTestingAvailable = try swiftCommandState.getHostToolchain().swiftSDK.supportsTesting
- if (toolchain.targetTriple.isDarwin() && toolchain.xctestPath == nil) || !isHostTestingAvailable {
- throw TestError.xctestNotAvailable
+ if case let .unsupported(reason) = try swiftCommandState.getHostToolchain().swiftSDK.xctestSupport {
+ throw TestError.xctestNotAvailable(reason: reason)
+ } else if toolchain.targetTriple.isDarwin() && toolchain.xctestPath == nil {
+ throw TestError.xctestNotAvailable()
  }
 
  let buildParameters = try swiftCommandState.buildParametersForTest(options: self.options, library: .xctest)
@@ -814,7 +819,7 @@ final class TestRunner {
  #if os(macOS)
  if library == .xctest {
  guard let xctestPath = self.toolchain.xctestPath else {
- throw TestError.xctestNotAvailable
+ throw TestError.xctestNotAvailable()
  }
  args = [xctestPath.pathString]
  args += additionalArguments

Sources/Commands/Utilities/TestingSupport.swift

@@ -178,11 +178,12 @@ enum TestingSupport {
  #endif
  return env
  #else
- // Add the sdk platform path if we have it. If this is not present, we might always end up failing.
- let sdkPlatformFrameworksPath = try SwiftSDK.sdkPlatformFrameworkPaths()
- // appending since we prefer the user setting (if set) to the one we inject
- env.appendPath("DYLD_FRAMEWORK_PATH", value: sdkPlatformFrameworksPath.fwk.pathString)
- env.appendPath("DYLD_LIBRARY_PATH", value: sdkPlatformFrameworksPath.lib.pathString)
+ // Add the sdk platform path if we have it.
+ if let sdkPlatformFrameworksPath = try? SwiftSDK.sdkPlatformFrameworkPaths() {
+ // appending since we prefer the user setting (if set) to the one we inject
+ env.appendPath("DYLD_FRAMEWORK_PATH", value: sdkPlatformFrameworksPath.fwk.pathString)
+ env.appendPath("DYLD_LIBRARY_PATH", value: sdkPlatformFrameworksPath.lib.pathString)
+ }
 
  // Fast path when no sanitizers are enabled.
  if sanitizers.isEmpty {

Sources/PackageModel/SwiftSDKs/SwiftSDK.swift

@@ -147,7 +147,29 @@ public struct SwiftSDK: Equatable {
  public var architectures: [String]? = nil
 
  /// Whether or not the receiver supports testing.
- public let supportsTesting: Bool
+ @available(*, deprecated, message: "Use `xctestSupport` instead")
+ public var supportsTesting: Bool {
+ if case .supported = xctestSupport {
+ return true
+ }
+ return false
+ }
+
+ /// Whether or not the receiver supports testing using XCTest.
+ public enum XCTestSupport: Sendable, Equatable {
+ /// XCTest is supported.
+ case supported
+
+ /// XCTest is not supported.
+ ///
+ /// - Parameters:
+ /// - reason: A string explaining why XCTest is not supported. If
+ /// `nil`, no additional information is available.
+ case unsupported(reason: String?)
+ }
+
+ /// Whether or not the receiver supports using XCTest.
+ public let xctestSupport: XCTestSupport
 
  /// Root directory path of the SDK used to compile for the target triple.
  @available(*, deprecated, message: "use `pathsConfiguration.sdkRootPath` instead")
@@ -417,19 +439,44 @@ public struct SwiftSDK: Equatable {
  )
  }
 
+ /// Creates a Swift SDK with the specified properties.
+ @available(*, deprecated, message: "use `init(hostTriple:targetTriple:toolset:pathsConfiguration:xctestSupport:)` instead")
+ public init(
+ hostTriple: Triple? = nil,
+ targetTriple: Triple? = nil,
+ toolset: Toolset,
+ pathsConfiguration: PathsConfiguration,
+ supportsTesting: Bool
+ ) {
+ let xctestSupport: XCTestSupport
+ if supportsTesting {
+ xctestSupport = .supported
+ } else {
+ xctestSupport = .unsupported(reason: nil)
+ }
+
+ self.init(
+ hostTriple: hostTriple,
+ targetTriple: targetTriple,
+ toolset: toolset,
+ pathsConfiguration: pathsConfiguration,
+ xctestSupport: xctestSupport
+ )
+ }
+
  /// Creates a Swift SDK with the specified properties.
  public init(
  hostTriple: Triple? = nil,
  targetTriple: Triple? = nil,
  toolset: Toolset,
  pathsConfiguration: PathsConfiguration,
- supportsTesting: Bool = true
+ xctestSupport: XCTestSupport = .supported
  ) {
  self.hostTriple = hostTriple
  self.targetTriple = targetTriple
  self.toolset = toolset
  self.pathsConfiguration = pathsConfiguration
- self.supportsTesting = supportsTesting
+ self.xctestSupport = xctestSupport
  }
 
  /// Returns the bin directory for the host.
@@ -496,7 +543,7 @@ public struct SwiftSDK: Equatable {
  #endif
 
  // Compute common arguments for clang and swift.
- let supportsTesting: Bool
+ let xctestSupport: XCTestSupport
  var extraCCFlags: [String] = []
  var extraSwiftCFlags: [String] = []
  #if os(macOS)
@@ -506,13 +553,12 @@ public struct SwiftSDK: Equatable {
  extraSwiftCFlags += ["-F", sdkPaths.fwk.pathString]
  extraSwiftCFlags += ["-I", sdkPaths.lib.pathString]
  extraSwiftCFlags += ["-L", sdkPaths.lib.pathString]
- supportsTesting = true
+ xctestSupport = .supported
  } catch {
- supportsTesting = false
- observabilityScope?.emit(warning: "could not determine XCTest paths: \(error)")
+ xctestSupport = .unsupported(reason: String(describing: error))
  }
  #else
- supportsTesting = true
+ xctestSupport = .supported
  #endif
 
  #if !os(Windows)
@@ -528,7 +574,7 @@ public struct SwiftSDK: Equatable {
  rootPaths: [binDir]
  ),
  pathsConfiguration: .init(sdkRootPath: sdkPath),
- supportsTesting: supportsTesting
+ xctestSupport: xctestSupport
  )
  }