Remove the Confirmation.ExpectedCount marker protocol. (#689)

This PR replaces uses of `Confirmation.ExpectedCount` in our API surface
with `RangeExpression<Int> & Sendable`. A composed protocol type `P<A> &
Q` can only be expressed as `some`, not `any` as the latter is not yet
implemented in the compiler (rdar://96960993), so we were using a
separate protocol in place of that combination.

The downside of doing so is that it makes the legibility of the
interface worse. Xcode and other IDEs will offer you
`confirmation(expectedCount: Confirmation.ExpectedCount)` but don't tell
you that you need to write some range expression such as `0...2`. You
have to dig into the protocol definition/documentation to figure it out.

So this change changes the signature of the experimental
`confirmation()` overload to take a `some RangeExpression<Int> &
Sendable` and plumbs that through everywhere it's valid. Once we get to
generating an `Issue`, we need an existential box (`any`) at which point
we will just drop the `<Int>` bit until the compiler feature is added.

We have a parameterized unit test that takes an array of these values,
so to keep it building and passing, I moved a copy of the
`ExpectedCount` protocol to the fixtures section of the test file
containing that test; it's present only in our test target and not in
our API surface.

### 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: grynspan

Sources/Testing/Issues/Confirmation.swift

@@ -164,7 +164,7 @@ public func confirmation<R>(
 @_spi(Experimental)
 public func confirmation<R>(
   _ comment: Comment? = nil,
-  expectedCount: some Confirmation.ExpectedCount,
+  expectedCount: some RangeExpression<Int> & Sendable,
   isolation: isolated (any Actor)? = #isolation,
   sourceLocation: SourceLocation = #_sourceLocation,
   _ body: (Confirmation) async throws -> sending R
@@ -200,22 +200,7 @@ public func confirmation<R>(
   fatalError("Unsupported")
 }
 
-@_spi(Experimental)
-extension Confirmation {
-  /// A protocol that describes a range expression that can be used with
-  /// ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-9rt6m``.
-  ///
-  /// This protocol represents any expression that describes a range of
-  /// confirmation counts. For example, the expression `1 ..< 10` automatically
-  /// conforms to it.
-  ///
-  /// You do not generally need to add conformances to this type yourself. It is
-  /// used by the testing library to abstract away the different range types
-  /// provided by the Swift standard library.
-  public protocol ExpectedCount: Sendable, RangeExpression<Int> {}
-}
-
-extension Confirmation.ExpectedCount {
+extension RangeExpression where Bound == Int, Self: Sendable {
   /// Get an instance of ``Issue/Kind-swift.enum`` corresponding to this value.
   ///
   /// - Parameters:
@@ -233,18 +218,3 @@ extension Confirmation.ExpectedCount {
     }
   }
 }
-
-@_spi(Experimental)
-extension ClosedRange<Int>: Confirmation.ExpectedCount {}
-
-@_spi(Experimental)
-extension PartialRangeFrom<Int>: Confirmation.ExpectedCount {}
-
-@_spi(Experimental)
-extension PartialRangeThrough<Int>: Confirmation.ExpectedCount {}
-
-@_spi(Experimental)
-extension PartialRangeUpTo<Int>: Confirmation.ExpectedCount {}
-
-@_spi(Experimental)
-extension Range<Int>: Confirmation.ExpectedCount {}

Sources/Testing/Issues/Issue.swift

@@ -52,7 +52,7 @@ public struct Issue: Sendable {
     /// the confirmation passed to these functions' `body` closures is confirmed
     /// too few or too many times.
     @_spi(Experimental)
-    indirect case confirmationOutOfRange(actual: Int, expected: any Confirmation.ExpectedCount)
+    indirect case confirmationOutOfRange(actual: Int, expected: any RangeExpression & Sendable)
 
     /// An issue due to an `Error` being thrown by a test function and caught by
     /// the testing library.
@@ -246,8 +246,14 @@ extension Issue {
     ///
     /// - Parameter issue: The original issue that gets snapshotted.
     public init(snapshotting issue: borrowing Issue) {
-      self.kind = Issue.Kind.Snapshot(snapshotting: issue.kind)
-      self.comments = issue.comments
+      if case .confirmationOutOfRange = issue.kind {
+        // Work around poor stringification of this issue kind in Xcode 16.
+        self.kind = .unconditional
+        self.comments = CollectionOfOne("\(issue.kind)") + issue.comments
+      } else {
+        self.kind = Issue.Kind.Snapshot(snapshotting: issue.kind)
+        self.comments = issue.comments
+      }
       self.sourceContext = issue.sourceContext
       self.isKnown = issue.isKnown
     }

Tests/TestingTests/ConfirmationTests.swift

@@ -116,16 +116,28 @@ struct UnsuccessfulConfirmationTests {
   }
 
   @Test(.hidden, arguments: [
-    1 ... 2 as any Confirmation.ExpectedCount,
+    1 ... 2 as any ExpectedCount,
     1 ..< 2,
     1 ..< 3,
     ..<2,
     ...2,
     999...,
   ])
-  func confirmedOutOfRange(_ range: any Confirmation.ExpectedCount) async {
+  func confirmedOutOfRange(_ range: any ExpectedCount) async {
     await confirmation(expectedCount: range) { (thingHappened) async in
       thingHappened(count: 3)
     }
   }
 }
+
+// MARK: -
+
+/// Needed since we don't have generic test functions, so we need a concrete
+/// argument type for `confirmedOutOfRange(_:)`, but we can't write
+/// `any RangeExpression<Int> & Sendable`. ([96960993](rdar://96960993))
+protocol ExpectedCount: RangeExpression, Sendable where Bound == Int {}
+extension ClosedRange<Int>: ExpectedCount {}
+extension PartialRangeFrom<Int>: ExpectedCount {}
+extension PartialRangeThrough<Int>: ExpectedCount {}
+extension PartialRangeUpTo<Int>: ExpectedCount {}
+extension Range<Int>: ExpectedCount {}