Replace fixture protocol in ConfirmationTests with an existential composition of parameterized protocols (#1598)

This modifies a test fixture in `ConfirmationTests` now that both a
Swift language limitation, and an associated runtime bug, have been
resolved.

The original issue was that the language did not support writing `any
RangeExpression<Int> & Sequence<Int> & Sendable`, but that was resolved
in Swift 6.2 in swiftlang/swift#76705. Once that
was resolved, it exposed a runtime bug which would crash when forming a
collection of such existential types. That was fixed in
swiftlang/swift#85346, and landed in Apple's
26.4 OSes (currently in beta).

This PR finally removes the workaround and writes this parameterized
test the idiomatic way, using a collection whose element type is a
composition of protocols where some are parameterized.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: stmontgomery

Package.swift

@@ -432,6 +432,7 @@ extension Array where Element == PackageDescription.SwiftSetting {
       .enableExperimentalFeature("AvailabilityMacro=_clockAPI:macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0"),
       .enableExperimentalFeature("AvailabilityMacro=_typedThrowsAPI:macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0"),
       .enableExperimentalFeature("AvailabilityMacro=_castingWithNonCopyableGenerics:macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0"),
+      .enableExperimentalFeature("AvailabilityMacro=_compositionOfParameterizedProtocols:macOS 26.4, iOS 26.4, watchOS 26.4, tvOS 26.4, visionOS 26.4"),
 
       .enableExperimentalFeature("AvailabilityMacro=_distantFuture:macOS 99.0, iOS 99.0, watchOS 99.0, tvOS 99.0, visionOS 99.0"),
     ]

Tests/TestingTests/ConfirmationTests.swift

@@ -33,7 +33,14 @@ struct ConfirmationTests {
 
   @Test("Unsuccessful confirmations")
   func unsuccessfulConfirmations() async {
-    await confirmation("Miscount recorded", expectedCount: 7) { miscountRecorded in
+    // confirmedOutOfRange(_:) is availability-guarded, but if it runs, increase
+    // the number of expected miscounts by the number of arguments passed to it.
+    var expectedCount = 7
+    if #available(_compositionOfParameterizedProtocols, *) {
+      expectedCount += 4
+    }
+
+    await confirmation("Miscount recorded", expectedCount: expectedCount) { miscountRecorded in
       var configuration = Configuration()
       configuration.eventHandler = { event, _ in
         if case let .issueRecorded(issue) = event.kind {
@@ -152,13 +159,28 @@ struct UnsuccessfulConfirmationTests {
     }
   }
 
+  // FIXME: Remove this test once the deployment targets are greater than or
+  // equal to the versions specified in `_compositionOfParameterizedProtocols`.
   @Test(.hidden, arguments: [
     1 ... 2 as any ExpectedCount,
     1 ..< 2,
     1 ..< 3,
     999...,
   ])
-  func confirmedOutOfRange(_ range: any ExpectedCount) async {
+  func confirmedOutOfRange_legacy(_ range: any ExpectedCount) async {
+    await confirmation(expectedCount: range) { (thingHappened) async in
+      thingHappened(count: 3)
+    }
+  }
+
+  @Test(.hidden, arguments: [
+    1 ... 2 as any RangeExpression<Int> & Sequence<Int> & Sendable,
+    1 ..< 2,
+    1 ..< 3,
+    999...,
+  ])
+  @available(_compositionOfParameterizedProtocols, *)
+  func confirmedOutOfRange(_ range: any RangeExpression<Int> & Sequence<Int> & Sendable) async {
     await confirmation(expectedCount: range) { (thingHappened) async in
       thingHappened(count: 3)
     }
@@ -168,7 +190,7 @@ struct UnsuccessfulConfirmationTests {
 // MARK: -
 
 /// Needed since we don't have generic test functions, so we need a concrete
-/// argument type for `confirmedOutOfRange(_:)`. Although we can now write
+/// argument type for `confirmedOutOfRange_legacy(_:)`. Although we can now write
 /// `any RangeExpression<Int> & Sequence<Int> & Sendable` as of Swift 6.2
 /// (per [swiftlang/swift#76705](https://github.com/swiftlang/swift/pull/76705)),
 /// attempting to form an array of such values crashes at runtime. ([163980446](rdar://163980446))

cmake/modules/shared/AvailabilityDefinitions.cmake

@@ -14,4 +14,5 @@ add_compile_options(
   "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -define-availability -Xfrontend \"_clockAPI:macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0\">"
   "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -define-availability -Xfrontend \"_typedThrowsAPI:macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0\">"
   "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -define-availability -Xfrontend \"_castingWithNonCopyableGenerics:macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0\">"
+  "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -define-availability -Xfrontend \"_compositionOfParameterizedProtocols:macOS 26.4, iOS 26.4, watchOS 26.4, tvOS 26.4, visionOS 26.4\">"
   "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -define-availability -Xfrontend \"_distantFuture:macOS 99.0, iOS 99.0, watchOS 99.0, tvOS 99.0, visionOS 99.0\">")