Remove legacy test content discovery. (#1013)

This PR removes the legacy test content discovery mechanism that is
based on finding protocol conformances in the type metadata section
emitted by the Swift compiler.

### 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

Documentation/EnvironmentVariables.md

@@ -67,6 +67,5 @@ names prefixed with `SWT_`.
 | `SWIFT_TESTING_XCTEST_INTEROP_MODE` | `String` | Overrides the behavior for handling XCTest assertion failures recorded during a Swift Testing test. One of `none`, `limited`, `complete`, or `strict`. Explanation of modes can be found in [ST-0021][interop-modes]. | <!--prefer to link to MigratingFromXCTest.md once it is updated with interop-->
 | `SWT_EXPERIMENTAL_SERIALIZED_TRAIT_APPLIES_GLOBALLY` | `Bool` | Whether or not `.serialized` applies globally or just to its branch of the test graph. |
 | `SWT_EXPERIMENTAL_MAXIMUM_PARALLELIZATION_WIDTH` | `Int` | The default parallelization width when parallelized testing is enabled. |
-| `SWT_USE_LEGACY_TEST_DISCOVERY` | `Bool` | Used to explicitly enable or disable legacy test discovery. |
 
 [interop-modes]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/testing/0021-targeted-interoperability-swift-testing-and-xctest.md#interoperability-modes

Documentation/Porting.md

@@ -131,13 +131,9 @@ When porting to a new platform, you may need to provide a new implementation for
 on Swift metadata discovery which is an inherently platform-specific operation.
 
 _Most_ platforms in use today use the ELF image format and will be able to reuse
-the implementation used by Linux, FreeBSD, etc.
-
-> [!NOTE]
-> We are not using `objectFormat()` in this file yet in order to maintain
-> compatibility with the Swift 6.2 toolchain. We will migrate to
-> `objectFormat()` when the `_TestDiscovery` target drops Swift 6.2 toolchain
-> support in the future.
+the implementation used by Linux, FreeBSD, etc. On platforms that use the ELF
+image format, the Swift runtime exports a function that Swift Testing uses
+during test discovery, and you likely do not need to make changes here.
 
 Classic does not use the ELF image format, so you'll need to write a custom
 implementation of `_sectionBounds(_:)` instead. Assuming that the Swift compiler
@@ -150,15 +146,11 @@ to load that information:
 +++ b/Sources/_TestDiscovery/SectionBounds.swift
 
  // ...
-+#elseif os(Classic)
++#elseif os(Classic) && objectFormat(CFM)
 +private func _sectionBounds(_ kind: SectionBounds.Kind) -> [SectionBounds] {
 +  let resourceName: Str255 = switch kind {
 +  case .testContent:
 +    "__swift5_tests"
-+#if !SWT_NO_LEGACY_TEST_DISCOVERY
-+  case .typeMetadata:
-+    "__swift5_types"
-+#endif
 +  }
 +
 +  let oldRefNum = CurResFile()
@@ -206,6 +198,7 @@ platform if it does not use an image format already supported by Swift Testing:
 ```diff
 --- a/Sources/TestingMacros/Support/TestContentGeneration.swift
 +++ b/Sources/TestingMacros/Support/TestContentGeneration.swift
+
    let objectFormatsAndSectionNames: [(objectFormat: String, sectionName: String)] = [
      ("MachO", "__DATA_CONST,__swift5_tests"),
      ("ELF", "swift5_tests"),
@@ -220,9 +213,8 @@ platform if it does not use an image format already supported by Swift Testing:
 If your platform does not support dynamic linking and loading, you will need to
 use static linkage instead. Define the `"SWT_NO_DYNAMIC_LINKING"` compiler
 conditional for your platform in both `Package.swift` and
-`CompilerSettings.cmake`, then define the symbols `_testContentSectionBegin`,
-`_testContentSectionEnd`, `_typeMetadataSectionBegin`, and
-`_typeMetadataSectionEnd` in `SectionBounds.swift`:
+`CompilerSettings.cmake`, then define the symbols `_testContentSectionBegin` and
+`_testContentSectionEnd` in `SectionBounds.swift`:
 
 ```diff
 --- a/Sources/_TestDiscovery/SectionBounds.swift
@@ -231,18 +223,10 @@ conditional for your platform in both `Package.swift` and
 +#elseif os(Classic)
 +@_silgen_name(raw: "...") private nonisolated(unsafe) var _testContentSectionBegin: _SectionBound
 +@_silgen_name(raw: "...") private nonisolated(unsafe) var _testContentSectionEnd: _SectionBound
-+#if !SWT_NO_LEGACY_TEST_DISCOVERY
-+@_silgen_name(raw: "...") private nonisolated(unsafe) var _typeMetadataSectionBegin: _SectionBound
-+@_silgen_name(raw: "...") private nonisolated(unsafe) var _typeMetadataSectionEnd: _SectionBound
-+#endif
  #else
  #warning("Platform-specific implementation missing: Runtime test discovery unavailable (static)")
  private nonisolated(unsafe) let _testContentSectionBegin = UnsafeMutableRawPointer.allocate(byteCount: 1, alignment: 16)
  private nonisolated(unsafe) let _testContentSectionEnd = _testContentSectionBegin
- #if !SWT_NO_LEGACY_TEST_DISCOVERY
- private nonisolated(unsafe) let _typeMetadataSectionBegin = UnsafeMutableRawPointer.allocate(byteCount: 1, alignment: 16)
- private nonisolated(unsafe) let _typeMetadataSectionEnd = _typeMetadataSectionBegin
- #endif
  #endif
  // ...
 ```

Package.swift

@@ -514,7 +514,6 @@ extension Array where Element: _LanguageBuildSetting {
       "SWT_NO_GLOBAL_ACTORS": (platforms: .none, embedded: true),
       "SWT_NO_SUSPENDING_CLOCK": (platforms: .none, embedded: true),
 
-      "SWT_NO_LEGACY_TEST_DISCOVERY": (platforms: .none, embedded: true),
       "SWT_NO_LIBDISPATCH": (platforms: .none, embedded: true),
     ]
 

Sources/Testing/CMakeLists.txt

@@ -111,7 +111,6 @@ add_library(Testing
   Test.swift
   Test+Cancellation.swift
   Test+Discovery.swift
-  Test+Discovery+Legacy.swift
   Test+Macro.swift
   Traits/AttachmentSavingTrait.swift
   Traits/Bug.swift

Sources/Testing/ExitTests/ExitTest.swift

@@ -435,15 +435,6 @@ extension ExitTest {
       }
     }
 
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-    // Call the legacy lookup function that discovers tests embedded in types.
-    for record in Record.allTypeMetadataBasedTestContentRecords() {
-      if let exitTest = record.load(withHint: id)?.makeExitTest() {
-        return exitTest
-      }
-    }
-#endif
-
     return nil
   }
 }

Sources/Testing/Test+Discovery+Legacy.swift

@@ -63,51 +63,17 @@ extension Test {
       // defective test records.)
       var result = Set<Self>()
 
-      // Figure out which discovery mechanism to use. By default, we'll use both
-      // the legacy and new mechanisms, but we can set an environment variable
-      // to explicitly select one or the other. When we remove legacy support,
-      // we can also remove this enumeration and environment variable check.
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-      let (useNewMode, useLegacyMode) = switch Environment.flag(named: "SWT_USE_LEGACY_TEST_DISCOVERY") {
-      case .none:
-        (true, true)
-      case .some(true):
-        (false, true)
-      case .some(false):
-        (true, false)
-      }
-#else
-      let useNewMode = true
-#endif
-
       // Walk all test content and gather generator functions, then call them in
       // a task group and collate their results.
-      if useNewMode {
-        let generators = Generator.allTestContentRecords().lazy.compactMap { $0.load() }
-        await withTaskGroup { taskGroup in
-          for (i, generator) in generators.enumerated() {
-            taskGroup.addTask(name: decorateTaskName("test discovery", withAction: "loading test #\(i)")) {
-              await generator.rawValue()
-            }
-          }
-          result = await taskGroup.reduce(into: result) { $0.insert($1) }
-        }
-      }
-
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-      // Perform legacy test discovery if needed.
-      if useLegacyMode && result.isEmpty {
-        let generators = Generator.allTypeMetadataBasedTestContentRecords().lazy.compactMap { $0.load() }
-        await withTaskGroup { taskGroup in
-          for (i, generator) in generators.enumerated() {
-            taskGroup.addTask(name: decorateTaskName("type-based test discovery", withAction: "loading test #\(i)")) {
-              await generator.rawValue()
-            }
+      let generators = Generator.allTestContentRecords().lazy.compactMap { $0.load() }
+      await withTaskGroup(of: Self.self) { taskGroup in
+        for (i, generator) in generators.enumerated() {
+          taskGroup.addTask(name: decorateTaskName("test discovery", withAction: "loading test #\(i)")) {
+            await generator.rawValue()
           }
-          result = await taskGroup.reduce(into: result) { $0.insert($1) }
         }
+        result = await taskGroup.reduce(into: result) { $0.insert($1) }
       }
-#endif
 
       return result
     }

Sources/Testing/Test+Discovery.swift

@@ -39,19 +39,4 @@ public protocol DiscoverableAsTestContent: Sendable {
   /// By default, this type equals `Never`, indicating that this type of test
   /// content does not support hinting during discovery.
   associatedtype TestContentAccessorHint = Never
-
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-  /// A string present in the names of types containing test content records
-  /// associated with this type.
-  @available(swift, deprecated: 100000.0, message: "Do not adopt this functionality in new code. It will be removed in a future release.")
-  static var _testContentTypeNameHint: String { get }
-#endif
-}
-
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-extension DiscoverableAsTestContent {
-  public static var _testContentTypeNameHint: String {
-    "__🟡$"
-  }
 }
-#endif

Sources/_TestDiscovery/DiscoverableAsTestContent.swift

@@ -26,11 +26,6 @@ struct SectionBounds: Sendable, BitwiseCopyable {
   enum Kind: Int, Equatable, Hashable, CaseIterable {
     /// The test content metadata section.
     case testContent
-
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-    /// The type metadata section.
-    case typeMetadata
-#endif
   }
 
   /// All section bounds of the given kind found in the current process.
@@ -45,7 +40,7 @@ struct SectionBounds: Sendable, BitwiseCopyable {
   }
 }
 
-#if SWT_TARGET_OS_APPLE && !SWT_NO_DYNAMIC_LINKING
+#if SWT_TARGET_OS_APPLE && objectFormat(MachO) && !SWT_NO_DYNAMIC_LINKING
 // MARK: - Apple implementation
 
 extension SectionBounds.Kind {
@@ -61,10 +56,6 @@ extension SectionBounds.Kind {
     switch self {
     case .testContent:
       ("__DATA_CONST", "__swift5_tests")
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-    case .typeMetadata:
-      ("__TEXT", "__swift5_types")
-#endif
     }
   }
 }
@@ -193,7 +184,7 @@ private func _sectionBounds(_ kind: SectionBounds.Kind) -> some RandomAccessColl
 #endif
 }
 
-#elseif (os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android)) && !SWT_NO_DYNAMIC_LINKING
+#elseif objectFormat(ELF) && !SWT_NO_DYNAMIC_LINKING
 // MARK: - ELF implementation
 
 private import SwiftShims // For MetadataSections
@@ -226,10 +217,6 @@ private func _sectionBounds(_ kind: SectionBounds.Kind) -> [SectionBounds] {
       let range = switch context.pointee.kind {
       case .testContent:
         sections.swift5_tests
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-      case .typeMetadata:
-        sections.swift5_type_metadata
-#endif
       }
       let start = UnsafeRawPointer(bitPattern: range.start)
       let size = Int(clamping: range.length)
@@ -247,7 +234,7 @@ private func _sectionBounds(_ kind: SectionBounds.Kind) -> [SectionBounds] {
   return context.result
 }
 
-#elseif os(Windows)
+#elseif os(Windows) && objectFormat(COFF)
 // MARK: - Windows implementation
 
 /// Find the section with the given name in the given module.
@@ -319,10 +306,6 @@ private func _sectionBounds(_ kind: SectionBounds.Kind) -> some Sequence<Section
   let sectionName = switch kind {
   case .testContent:
     ".sw5test"
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-  case .typeMetadata:
-    ".sw5tymd"
-#endif
   }
   return HMODULE.all.lazy.compactMap { _findSection(named: sectionName, in: $0) }
 }
@@ -367,28 +350,16 @@ private struct _SectionBound: Sendable, ~Copyable {
   }
 }
 
-#if SWT_TARGET_OS_APPLE
+#if objectFormat(MachO)
 @_silgen_name(raw: "section$start$__DATA_CONST$__swift5_tests") private nonisolated(unsafe) var _testContentSectionBegin: _SectionBound
 @_silgen_name(raw: "section$end$__DATA_CONST$__swift5_tests") private nonisolated(unsafe) var _testContentSectionEnd: _SectionBound
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-@_silgen_name(raw: "section$start$__TEXT$__swift5_types") private nonisolated(unsafe) var _typeMetadataSectionBegin: _SectionBound
-@_silgen_name(raw: "section$end$__TEXT$__swift5_types") private nonisolated(unsafe) var _typeMetadataSectionEnd: _SectionBound
-#endif
-#elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#elseif objectFormat(ELF) || objectFormat(Wasm)
 @_silgen_name(raw: "__start_swift5_tests") private nonisolated(unsafe) var _testContentSectionBegin: _SectionBound
 @_silgen_name(raw: "__stop_swift5_tests") private nonisolated(unsafe) var _testContentSectionEnd: _SectionBound
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-@_silgen_name(raw: "__start_swift5_type_metadata") private nonisolated(unsafe) var _typeMetadataSectionBegin: _SectionBound
-@_silgen_name(raw: "__stop_swift5_type_metadata") private nonisolated(unsafe) var _typeMetadataSectionEnd: _SectionBound
-#endif
 #else
 #warning("Platform-specific implementation missing: Runtime test discovery unavailable (static)")
 private nonisolated(unsafe) let _testContentSectionBegin = UnsafeMutableRawPointer.allocate(byteCount: 1, alignment: 16)
 private nonisolated(unsafe) let _testContentSectionEnd = _testContentSectionBegin
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-private nonisolated(unsafe) let _typeMetadataSectionBegin = UnsafeMutableRawPointer.allocate(byteCount: 1, alignment: 16)
-private nonisolated(unsafe) let _typeMetadataSectionEnd = _typeMetadataSectionBegin
-#endif
 #endif
 
 /// The common implementation of ``SectionBounds/all(_:)`` for platforms that do
@@ -403,10 +374,6 @@ private func _sectionBounds(_ kind: SectionBounds.Kind) -> CollectionOfOne<Secti
   let range = switch kind {
   case .testContent:
     _testContentSectionBegin ..< _testContentSectionEnd
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
-  case .typeMetadata:
-    _typeMetadataSectionBegin ..< _typeMetadataSectionEnd
-#endif
   }
   let buffer = UnsafeRawBufferPointer(start: range.lowerBound, count: range.count)
   let sb = SectionBounds(imageAddress: nil, buffer: buffer)