Acknowledge unsafe API usages in code expanded from testing library macros (#1134)

Acknowledge unsafe API usages from various testing library macros such
as `@Test`, `@Suite`, and `#expect(processExitsWith:)` which are
revealed in modules which enable the new opt-in strict memory safety
feature in Swift 6.2.

### Motivation:

This fix allows clients of the testing library to enable [SE-0458:
Opt-in Strict Memory Safety
Checking](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0458-strict-memory-safety.md)
if they wish and avoid diagnostics from the testing library macros in
their modules. These warnings generally looked like this, before this
fix:

```
⚠️ @__swiftmacro_22MemorySafeTestingTests19exampleTestFunction33_F2EA1AA3013574E5644E5A4339F05086LL0F0fMp_.swift:23:14: warning: expression uses unsafe constructs but is not marked with 'unsafe'
  Testing.Test.__store($s22MemorySafeTestingTests19exampleTestFunction33_F2EA1AA3013574E5644E5A4339F05086LL0F0fMp_25generator1e3470c498e8fe35fMu_, into: outValue, asTypeAt: type)
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

### Modifications:

- Add test file to reproduce the new diagnostics. It's in a new module
which opts-in to strict memory safety, and marked as a dependency of
`TestingTests`.
- Add `unsafe` keyword in the appropriate places in our macros to
acknowledge the existing unsafe usages.

### 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.

Fixes: rdar://151238560

Author: stmontgomery

Package.swift

@@ -127,10 +127,25 @@ let package = Package(
         "Testing",
         "_Testing_CoreGraphics",
         "_Testing_Foundation",
+        "MemorySafeTestingTests",
       ],
       swiftSettings: .packageSettings
     ),
 
+    // Use a plain `.target` instead of a `.testTarget` to avoid the unnecessary
+    // overhead of having a separate test target for this module. Conceptually,
+    // the content in this module is no different than content which would
+    // typically be placed in the `TestingTests` target, except this content
+    // needs the (module-wide) strict memory safety feature to be enabled.
+    .target(
+      name: "MemorySafeTestingTests",
+      dependencies: [
+        "Testing",
+      ],
+      path: "Tests/_MemorySafeTestingTests",
+      swiftSettings: .packageSettings + .strictMemorySafety
+    ),
+
     .macro(
       name: "TestingMacros",
       dependencies: [
@@ -355,6 +370,18 @@ extension Array where Element == PackageDescription.SwiftSetting {
 
     return result
   }
+
+  /// Settings necessary to enable Strict Memory Safety, introduced in
+  /// [SE-0458: Opt-in Strict Memory Safety Checking](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0458-strict-memory-safety.md#swiftpm-integration).
+  static var strictMemorySafety: Self {
+#if compiler(>=6.2)
+    // FIXME: Adopt official `.strictMemorySafety()` condition once the minimum
+    // supported toolchain is 6.2.
+    [.unsafeFlags(["-strict-memory-safety"])]
+#else
+    []
+#endif
+  }
 }
 
 extension Array where Element == PackageDescription.CXXSetting {

Sources/Testing/ExitTests/ExitTest.swift

@@ -327,6 +327,9 @@ extension ExitTest {
   ///
   /// - Warning: This function is used to implement the
   ///   `#expect(processExitsWith:)` macro. Do not use it directly.
+#if compiler(>=6.2)
+  @safe
+#endif
   public static func __store<each T>(
     _ id: (UInt64, UInt64, UInt64, UInt64),
     _ body: @escaping @Sendable (repeat each T) async throws -> Void,

Sources/Testing/Test+Discovery.swift

@@ -39,6 +39,9 @@ extension Test {
   ///
   /// - Warning: This function is used to implement the `@Test` macro. Do not
   ///   use it directly.
+#if compiler(>=6.2)
+  @safe
+#endif
   public static func __store(
     _ generator: @escaping @Sendable () async -> Test,
     into outValue: UnsafeMutableRawPointer,

Sources/TestingMacros/ConditionMacro.swift

@@ -496,10 +496,11 @@ extension ExitTestConditionMacro {
       var recordDecl: DeclSyntax?
 #if !SWT_NO_LEGACY_TEST_DISCOVERY
       let legacyEnumName = context.makeUniqueName("__🟡$")
+      let unsafeKeyword: TokenSyntax? = isUnsafeKeywordSupported ? .keyword(.unsafe, trailingTrivia: .space) : nil
       recordDecl = """
       enum \(legacyEnumName): Testing.__TestContentRecordContainer {
         nonisolated static var __testContentRecord: Testing.__TestContentRecord {
-          \(enumName).testContentRecord
+          \(unsafeKeyword)\(enumName).testContentRecord
         }
       }
       """

Sources/TestingMacros/SuiteDeclarationMacro.swift

@@ -169,12 +169,13 @@ public struct SuiteDeclarationMacro: MemberMacro, PeerMacro, Sendable {
 #if !SWT_NO_LEGACY_TEST_DISCOVERY
     // Emit a type that contains a reference to the test content record.
     let enumName = context.makeUniqueName("__🟡$")
+    let unsafeKeyword: TokenSyntax? = isUnsafeKeywordSupported ? .keyword(.unsafe, trailingTrivia: .space) : nil
     result.append(
       """
       @available(*, deprecated, message: "This type is an implementation detail of the testing library. Do not use it directly.")
       enum \(enumName): Testing.__TestContentRecordContainer {
         nonisolated static var __testContentRecord: Testing.__TestContentRecord {
-          \(testContentRecordName)
+          \(unsafeKeyword)\(testContentRecordName)
         }
       }
       """

Sources/TestingMacros/Support/EffectfulExpressionHandling.swift

@@ -86,6 +86,17 @@ extension BidirectionalCollection<Syntax> {
 
 // MARK: - Inserting effect keywords/thunks
 
+/// Whether or not the `unsafe` expression keyword is supported.
+var isUnsafeKeywordSupported: Bool {
+  // The 'unsafe' keyword was introduced in 6.2 as part of SE-0458. Older
+  // toolchains are not aware of it.
+#if compiler(>=6.2)
+  true
+#else
+  false
+#endif
+}
+
 /// Make a function call expression to an effectful thunk function provided by
 /// the testing library.
 ///
@@ -127,12 +138,7 @@ func applyEffectfulKeywords(_ effectfulKeywords: Set<Keyword>, to expr: some Exp
   let needAwait = effectfulKeywords.contains(.await) && !expr.is(AwaitExprSyntax.self)
   let needTry = effectfulKeywords.contains(.try) && !expr.is(TryExprSyntax.self)
 
-  // The 'unsafe' keyword was introduced in 6.2 as part of SE-0458. Older
-  // toolchains are not aware of it, so avoid emitting expressions involving
-  // that keyword when the macro has been built using an older toolchain.
-#if compiler(>=6.2)
-  let needUnsafe = effectfulKeywords.contains(.unsafe) && !expr.is(UnsafeExprSyntax.self)
-#endif
+  let needUnsafe = isUnsafeKeywordSupported && effectfulKeywords.contains(.unsafe) && !expr.is(UnsafeExprSyntax.self)
 
   // First, add thunk function calls.
   if needAwait {
@@ -141,41 +147,37 @@ func applyEffectfulKeywords(_ effectfulKeywords: Set<Keyword>, to expr: some Exp
   if needTry {
     expr = _makeCallToEffectfulThunk(.identifier("__requiringTry"), passing: expr)
   }
-#if compiler(>=6.2)
   if needUnsafe {
     expr = _makeCallToEffectfulThunk(.identifier("__requiringUnsafe"), passing: expr)
   }
-#endif
 
   // Then add keyword expressions. (We do this separately so we end up writing
   // `try await __r(__r(self))` instead of `try __r(await __r(self))` which is
   // less accepted by the compiler.)
   if needAwait {
     expr = ExprSyntax(
       AwaitExprSyntax(
-        awaitKeyword: .keyword(.await).with(\.trailingTrivia, .space),
+        awaitKeyword: .keyword(.await, trailingTrivia: .space),
         expression: expr
       )
     )
   }
   if needTry {
     expr = ExprSyntax(
       TryExprSyntax(
-        tryKeyword: .keyword(.try).with(\.trailingTrivia, .space),
+        tryKeyword: .keyword(.try, trailingTrivia: .space),
         expression: expr
       )
     )
   }
-#if compiler(>=6.2)
   if needUnsafe {
     expr = ExprSyntax(
       UnsafeExprSyntax(
-        unsafeKeyword: .keyword(.unsafe).with(\.trailingTrivia, .space),
+        unsafeKeyword: .keyword(.unsafe, trailingTrivia: .space),
         expression: expr
       )
     )
   }
-#endif
 
   expr.leadingTrivia = originalExpr.leadingTrivia
   expr.trailingTrivia = originalExpr.trailingTrivia

Sources/TestingMacros/Support/TestContentGeneration.swift

@@ -63,12 +63,13 @@ func makeTestContentRecordDecl(named name: TokenSyntax, in typeName: TypeSyntax?
     IntegerLiteralExprSyntax(context, radix: .binary)
   }
 
+  let unsafeKeyword: TokenSyntax? = isUnsafeKeywordSupported ? .keyword(.unsafe, trailingTrivia: .space) : nil
   var result: DeclSyntax = """
   @available(*, deprecated, message: "This property is an implementation detail of the testing library. Do not use it directly.")
   private nonisolated \(staticKeyword(for: typeName)) let \(name): Testing.__TestContentRecord = (
     \(kindExpr), \(kind.commentRepresentation)
     0,
-    \(accessorName),
+    \(unsafeKeyword)\(accessorName),
     \(contextExpr),
     0
   )

Sources/TestingMacros/TestDeclarationMacro.swift

@@ -494,12 +494,13 @@ public struct TestDeclarationMacro: PeerMacro, Sendable {
 #if !SWT_NO_LEGACY_TEST_DISCOVERY
     // Emit a type that contains a reference to the test content record.
     let enumName = context.makeUniqueName(thunking: functionDecl, withPrefix: "__🟡$")
+    let unsafeKeyword: TokenSyntax? = isUnsafeKeywordSupported ? .keyword(.unsafe, trailingTrivia: .space) : nil
     result.append(
       """
       @available(*, deprecated, message: "This type is an implementation detail of the testing library. Do not use it directly.")
       enum \(enumName): Testing.__TestContentRecordContainer {
         nonisolated static var __testContentRecord: Testing.__TestContentRecord {
-          \(testContentRecordName)
+          \(unsafeKeyword)\(testContentRecordName)
         }
       }
       """

Tests/_MemorySafeTestingTests/MemorySafeTestDecls.swift

@@ -0,0 +1,31 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+//
+
+#if compiler(>=6.2)
+
+@testable import Testing
+
+#if !hasFeature(StrictMemorySafety)
+#error("This file requires strict memory safety to be enabled")
+#endif
+
+@Test(.hidden)
+func exampleTestFunction() {}
+
+@Suite(.hidden)
+struct ExampleSuite {
+  @Test func example() {}
+}
+
+func exampleExitTest() async {
+  await #expect(processExitsWith: .success) {}
+}
+
+#endif