Make XCTestContext sendable (#74)

With concurrency warnings dialed up, this type can cause warnings to be
emitted, but as a task local should be safe to pass along.

Author: stephencelis

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.5
+// swift-tools-version:5.7
 
 import PackageDescription
 
@@ -22,7 +22,7 @@ let package = Package(
   ]
 )
 
-#if swift(>=5.6) && !os(Windows)
+#if !os(Windows)
   // Add the documentation compiler plugin if possible
   package.dependencies.append(
     .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0")

Sources/XCTestDynamicOverlay/Internal/GeneratePlaceholder.swift

@@ -17,133 +17,41 @@ private func _optionalPlaceholder<Result>() throws -> Result {
   throw PlaceholderGenerationFailure()
 }
 
-#if swift(>=5.7)
-  private func _placeholder<Result>() -> Result? {
-    switch Result.self {
-    case let type as _DefaultInitializable.Type: return type.placeholder as? Result
-    case is Void.Type: return () as? Result
-    case let type as any RangeReplaceableCollection.Type: return type.placeholder as? Result
-    case let type as any AdditiveArithmetic.Type: return type.placeholder as? Result
-    case let type as any ExpressibleByArrayLiteral.Type: return type.placeholder as? Result
-    case let type as any ExpressibleByBooleanLiteral.Type: return type.placeholder as? Result
-    case let type as any ExpressibleByDictionaryLiteral.Type: return type.placeholder as? Result
-    case let type as any ExpressibleByFloatLiteral.Type: return type.placeholder as? Result
-    case let type as any ExpressibleByIntegerLiteral.Type: return type.placeholder as? Result
-    case let type as any ExpressibleByUnicodeScalarLiteral.Type: return type.placeholder as? Result
-    default: return nil
-    }
-  }
-
-  private func _rawRepresentable<Result>() -> Result? {
-    func posiblePlaceholder<T: RawRepresentable>(for type: T.Type) -> T? {
-      (_placeholder() as T.RawValue?).flatMap(T.init(rawValue:))
-    }
-
-    return (Result.self as? any RawRepresentable.Type).flatMap {
-      posiblePlaceholder(for: $0) as? Result
-    }
-  }
-
-  private func _caseIterable<Result>() -> Result? {
-    func firstCase<T: CaseIterable>(for type: T.Type) -> Result? {
-      T.allCases.first as? Result
-    }
-
-    return (Result.self as? any CaseIterable.Type).flatMap {
-      firstCase(for: $0)
-    }
-  }
-#else
-  private func _placeholder<Result>() -> Result? {
-    if let result = (Result.self as? _DefaultInitializable.Type)?.placeholder {
-      return result as? Result
-    }
-
-    if Result.self == Void.self {
-      return () as? Result
-    }
-
-    switch Witness<Result>.self {
-    case let type as AnyRangeReplaceableCollection.Type: return type.placeholder as? Result
-    case let type as AnyAdditiveArithmetic.Type: return type.placeholder as? Result
-    case let type as AnyExpressibleByArrayLiteral.Type: return type.placeholder as? Result
-    case let type as AnyExpressibleByBooleanLiteral.Type: return type.placeholder as? Result
-    case let type as AnyExpressibleByDictionaryLiteral.Type: return type.placeholder as? Result
-    case let type as AnyExpressibleByFloatLiteral.Type: return type.placeholder as? Result
-    case let type as AnyExpressibleByIntegerLiteral.Type: return type.placeholder as? Result
-    case let type as AnyExpressibleByUnicodeScalarLiteral.Type: return type.placeholder as? Result
-    default: return nil
-    }
-  }
-
-  private func _rawRepresentable<Result>() -> Result? {
-    (Witness<Result>.self as? AnyRawRepresentable.Type).flatMap {
-      $0.possiblePlaceholder as? Result
-    }
-  }
-
-  private func _caseIterable<Result>() -> Result? {
-    (Witness<Result>.self as? AnyCaseIterable.Type).flatMap {
-      $0.firstCase as? Result
-    }
-  }
-
-  private enum Witness<Value> {}
-  private protocol AnyAdditiveArithmetic { static var placeholder: Any { get } }
-  extension Witness: AnyAdditiveArithmetic where Value: AdditiveArithmetic {
-    fileprivate static var placeholder: Any { Value.placeholder }
-  }
-
-  private protocol AnyExpressibleByArrayLiteral { static var placeholder: Any { get } }
-  extension Witness: AnyExpressibleByArrayLiteral where Value: ExpressibleByArrayLiteral {
-    fileprivate static var placeholder: Any { Value.placeholder }
-  }
-
-  private protocol AnyExpressibleByBooleanLiteral { static var placeholder: Any { get } }
-  extension Witness: AnyExpressibleByBooleanLiteral where Value: ExpressibleByBooleanLiteral {
-    fileprivate static var placeholder: Any { Value.placeholder }
-  }
-
-  private protocol AnyExpressibleByDictionaryLiteral { static var placeholder: Any { get } }
-  extension Witness: AnyExpressibleByDictionaryLiteral where Value: ExpressibleByDictionaryLiteral {
-    fileprivate static var placeholder: Any { Value.placeholder }
-  }
-
-  private protocol AnyExpressibleByFloatLiteral { static var placeholder: Any { get } }
-  extension Witness: AnyExpressibleByFloatLiteral where Value: ExpressibleByFloatLiteral {
-    fileprivate static var placeholder: Any { Value.placeholder }
-  }
-
-  private protocol AnyExpressibleByIntegerLiteral { static var placeholder: Any { get } }
-  extension Witness: AnyExpressibleByIntegerLiteral where Value: ExpressibleByIntegerLiteral {
-    fileprivate static var placeholder: Any { Value.placeholder }
+private func _placeholder<Result>() -> Result? {
+  switch Result.self {
+  case let type as _DefaultInitializable.Type: return type.placeholder as? Result
+  case is Void.Type: return () as? Result
+  case let type as any RangeReplaceableCollection.Type: return type.placeholder as? Result
+  case let type as any AdditiveArithmetic.Type: return type.placeholder as? Result
+  case let type as any ExpressibleByArrayLiteral.Type: return type.placeholder as? Result
+  case let type as any ExpressibleByBooleanLiteral.Type: return type.placeholder as? Result
+  case let type as any ExpressibleByDictionaryLiteral.Type: return type.placeholder as? Result
+  case let type as any ExpressibleByFloatLiteral.Type: return type.placeholder as? Result
+  case let type as any ExpressibleByIntegerLiteral.Type: return type.placeholder as? Result
+  case let type as any ExpressibleByUnicodeScalarLiteral.Type: return type.placeholder as? Result
+  default: return nil
   }
+}
 
-  private protocol AnyExpressibleByUnicodeScalarLiteral { static var placeholder: Any { get } }
-  extension Witness: AnyExpressibleByUnicodeScalarLiteral
-  where Value: ExpressibleByUnicodeScalarLiteral {
-    fileprivate static var placeholder: Any { Value.placeholder }
+private func _rawRepresentable<Result>() -> Result? {
+  func posiblePlaceholder<T: RawRepresentable>(for type: T.Type) -> T? {
+    (_placeholder() as T.RawValue?).flatMap(T.init(rawValue:))
   }
 
-  private protocol AnyRangeReplaceableCollection { static var placeholder: Any { get } }
-  extension Witness: AnyRangeReplaceableCollection where Value: RangeReplaceableCollection {
-    fileprivate static var placeholder: Any { Value.placeholder }
+  return (Result.self as? any RawRepresentable.Type).flatMap {
+    posiblePlaceholder(for: $0) as? Result
   }
+}
 
-  private protocol AnyRawRepresentable { static var possiblePlaceholder: Any? { get } }
-  extension Witness: AnyRawRepresentable where Value: RawRepresentable {
-    fileprivate static var possiblePlaceholder: Any? {
-      (_placeholder() as Value.RawValue?).flatMap(Value.init(rawValue:))
-    }
+private func _caseIterable<Result>() -> Result? {
+  func firstCase<T: CaseIterable>(for type: T.Type) -> Result? {
+    T.allCases.first as? Result
   }
 
-  private protocol AnyCaseIterable { static var firstCase: Any? { get } }
-  extension Witness: AnyCaseIterable where Value: CaseIterable {
-    fileprivate static var firstCase: Any? {
-      Value.allCases.first
-    }
+  return (Result.self as? any CaseIterable.Type).flatMap {
+    firstCase(for: $0)
   }
-#endif
+}
 
 struct PlaceholderGenerationFailure: Error {}
 func _generatePlaceholder<Result>() throws -> Result {

Sources/XCTestDynamicOverlay/XCTFail.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-public struct XCTFailContext {
+public struct XCTFailContext: Sendable {
   @TaskLocal public static var current: Self?
 
   public var file: StaticString