Adopt @section and @used. (#1408)

This PR adopts the `@section` and `@used` attributes now available in
the Swift 6.3 toolchain. These attributes replace the experimental
`@_section` and `@_used` attributes verbatim and they are always enabled
(so no need to check `hasFeature(SymbolLinkageMarkers)`.)

Because these attributes are only available with the Swift 6.3
toolchain, we do not use them when building with Swift 6.2. Instead, if
you build with Swift 6.2 you continue to use the "legacy" test discovery
mechanism based on type metadata emission. The "legacy" mechanism will
be removed in a future update.

Because the `_TestDiscovery` target needs to continue to compile with
Swift 6.2, I have not switched us over to `objectFormat()` yet. See
#1370 for details.

Resolves #1371.
Resolves rdar://136789701.

### 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/Porting.md

@@ -193,7 +193,7 @@ to load that information:
 ```
 
 You will also need to update the `makeTestContentRecordDecl()` function in the
-`TestingMacros` target to emit the correct `@_section` attribute for your
+`TestingMacros` target to emit the correct `@section` attribute for your
 platform. If your platform uses the ELF image format and supports the
 `dl_iterate_phdr()` function, add it to the existing `#elseif os(Linux) || ...`
 case. Otherwise, add a new case for your platform:
@@ -203,7 +203,7 @@ case. Otherwise, add a new case for your platform:
 +++ b/Sources/TestingMacros/Support/TestContentGeneration.swift
    // ...
 +  #elseif os(Classic)
-+  @_section(".rsrc,swft,__swift5_tests")
++  @section(".rsrc,swft,__swift5_tests")
    #else
    @__testing(warning: "Platform-specific implementation missing: test content section name unavailable")
    #endif
@@ -214,6 +214,11 @@ directly into test authors' test targets, so you will not be able to use
 compiler conditionals defined in the Swift Testing package (including those that
 start with `"SWT_"`).
 
+> [!NOTE]
+> We are not using `objectFormat()` yet to maintain compatibility with the Swift
+> 6.2 toolchain. We will migrate to `objectFormat()` when we drop Swift 6.2
+> toolchain support (presumably after Swift 6.3 ships).
+
 ## Runtime test discovery with static linkage
 
 If your platform does not support dynamic linking and loading, you will need to

Package.swift

@@ -379,11 +379,6 @@ extension Array where Element == PackageDescription.SwiftSetting {
 
       .enableUpcomingFeature("MemberImportVisibility"),
 
-      // This setting is enabled in the package, but not in the toolchain build
-      // (via CMake). Enabling it is dependent on acceptance of the @section
-      // proposal via Swift Evolution.
-      .enableExperimentalFeature("SymbolLinkageMarkers"),
-
       // Enabled to allow tests to be added to ~Escapable suites.
       .enableExperimentalFeature("Lifetimes"),
 

Sources/Testing/Discovery+Macro.swift

@@ -34,7 +34,7 @@ public typealias __TestContentRecordAccessor = @convention(c) (
 public typealias __TestContentRecord = (
   kind: UInt32,
   reserved1: UInt32,
-  accessor: __TestContentRecordAccessor?,
+  accessor: __TestContentRecordAccessor,
   context: UInt,
   reserved2: UInt
 )

Sources/TestingMacros/ConditionMacro.swift

@@ -13,10 +13,6 @@ public import SwiftSyntax
 import SwiftSyntaxBuilder
 public import SwiftSyntaxMacros
 
-#if !hasFeature(SymbolLinkageMarkers) && SWT_NO_LEGACY_TEST_DISCOVERY
-#error("Platform-specific misconfiguration: either SymbolLinkageMarkers or legacy test discovery is required to expand #expect(processExitsWith:)")
-#endif
-
 /// A protocol containing the common implementation for the expansions of the
 /// `#expect()` and `#require()` macros.
 ///
@@ -496,7 +492,7 @@ extension ExitTestConditionMacro {
 
       // Create another local type for legacy test discovery.
       var recordDecl: DeclSyntax?
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
+#if compiler(<6.3)
       let legacyEnumName = context.makeUniqueName("__🟡$")
       recordDecl = """
       enum \(legacyEnumName): Testing.__TestContentRecordContainer {

Sources/TestingMacros/SuiteDeclarationMacro.swift

@@ -13,10 +13,6 @@ public import SwiftSyntax
 import SwiftSyntaxBuilder
 public import SwiftSyntaxMacros
 
-#if !hasFeature(SymbolLinkageMarkers) && SWT_NO_LEGACY_TEST_DISCOVERY
-#error("Platform-specific misconfiguration: either SymbolLinkageMarkers or legacy test discovery is required to expand @Suite")
-#endif
-
 /// A type describing the expansion of the `@Suite` attribute macro.
 ///
 /// This type is used to implement the `@Suite` attribute macro. Do not use it
@@ -166,7 +162,7 @@ public struct SuiteDeclarationMacro: MemberMacro, PeerMacro, Sendable {
       )
     )
 
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
+#if compiler(<6.3)
     // Emit a type that contains a reference to the test content record.
     let enumName = context.makeUniqueName("__🟡$")
     result.append(

Sources/TestingMacros/Support/TestContentGeneration.swift

@@ -68,26 +68,24 @@ func makeTestContentRecordDecl(named name: TokenSyntax, in typeName: TypeSyntax?
   private nonisolated \(staticKeyword(for: typeName)) let \(name): Testing.__TestContentRecord = (
     \(kindExpr), \(kind.commentRepresentation)
     0,
-    unsafe \(accessorName),
+    { unsafe \(accessorName)($0, $1, $2, $3) },
     \(contextExpr),
     0
   )
   """
 
-#if hasFeature(SymbolLinkageMarkers)
+#if compiler(>=6.3)
   result = """
-  #if hasFeature(SymbolLinkageMarkers)
   #if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
-  @_section("__DATA_CONST,__swift5_tests")
+  @section("__DATA_CONST,__swift5_tests")
   #elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
-  @_section("swift5_tests")
+  @section("swift5_tests")
   #elseif os(Windows)
-  @_section(".sw5test$B")
+  @section(".sw5test$B")
   #else
   @Testing.__testing(warning: "Platform-specific implementation missing: test content section name unavailable")
   #endif
-  @_used
-  #endif
+  @used
   \(result)
   """
 #endif

Sources/TestingMacros/TestDeclarationMacro.swift

@@ -13,10 +13,6 @@ public import SwiftSyntax
 import SwiftSyntaxBuilder
 public import SwiftSyntaxMacros
 
-#if !hasFeature(SymbolLinkageMarkers) && SWT_NO_LEGACY_TEST_DISCOVERY
-#error("Platform-specific misconfiguration: either SymbolLinkageMarkers or legacy test discovery is required to expand @Test")
-#endif
-
 /// A type describing the expansion of the `@Test` attribute macro.
 ///
 /// This type is used to implement the `@Test` attribute macro. Do not use it
@@ -491,7 +487,7 @@ public struct TestDeclarationMacro: PeerMacro, Sendable {
       )
     )
 
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
+#if compiler(<6.3)
     // Emit a type that contains a reference to the test content record.
     let enumName = context.makeUniqueName(thunking: functionDecl, withPrefix: "__🟡$")
     result.append(

Sources/_TestDiscovery/TestContentRecord.swift

@@ -244,7 +244,7 @@ extension DiscoverableAsTestContent {
     return SectionBounds.all(.testContent).lazy.flatMap { sb in
       sb.buffer.withMemoryRebound(to: _TestContentRecord.self) { records in
         (0 ..< records.count).lazy
-          .map { (records.baseAddress! + $0) as UnsafePointer<_TestContentRecord> }
+          .map { records.baseAddress! + $0 }
           .filter { $0.pointee.kind == kind }
           .map { TestContentRecord<Self>(imageAddress: sb.imageAddress, recordAddress: $0) }
       }

Tests/TestingMacrosTests/TestDeclarationMacroTests.swift

@@ -486,10 +486,11 @@ struct TestDeclarationMacroTests {
   func differentFunctionTypes(input: String, expectedTypeName: String?, otherCode: String?) throws {
     let (output, _) = try parse(input)
 
-#if hasFeature(SymbolLinkageMarkers)
-    #expect(output.contains("@_section"))
-#endif
-#if !SWT_NO_LEGACY_TEST_DISCOVERY
+#if compiler(>=6.3)
+    #expect(output.contains("@section"))
+    #expect(!output.contains("__TestContentRecordContainer"))
+#else
+    #expect(!output.contains("@section"))
     #expect(output.contains("__TestContentRecordContainer"))
 #endif
     if let expectedTypeName {

Tests/TestingTests/DiscoveryTests.swift

@@ -58,7 +58,7 @@ struct DiscoveryTests {
   }
 #endif
 
-#if !SWT_NO_DYNAMIC_LINKING && hasFeature(SymbolLinkageMarkers)
+#if compiler(>=6.3) && !SWT_NO_DYNAMIC_LINKING
   struct MyTestContent: DiscoverableAsTestContent {
     typealias TestContentAccessorHint = UInt32
 
@@ -81,16 +81,16 @@ struct DiscoveryTests {
     }
 
 #if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
-    @_section("__DATA_CONST,__swift5_tests")
+    @section("__DATA_CONST,__swift5_tests")
 #elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
-    @_section("swift5_tests")
+    @section("swift5_tests")
 #elseif os(Windows)
-    @_section(".sw5test$B")
+    @section(".sw5test$B")
 #else
     @__testing(warning: "Platform-specific implementation missing: test content section name unavailable")
 #endif
-    @_used
-    private static let record: __TestContentRecord = (
+    @used
+    fileprivate static let record: __TestContentRecord = (
       0xABCD1234,
       0,
       { outValue, type, hint, _ in
@@ -105,12 +105,12 @@ struct DiscoveryTests {
         _ = outValue.initializeMemory(as: Self.self, to: .init(value: expectedValue))
         return true
       },
-      UInt(truncatingIfNeeded: UInt64(0x0204060801030507)),
+      0x02040608,
       0
     )
   }
 
-  @Test func testDiscovery() async {
+  @Test func testDiscovery() {
     // Check the type of the test record sequence (it should be lazy.)
     let allRecordsSeq = MyTestContent.allTestContentRecords()
 #if SWT_FIXED_143080508
@@ -142,22 +142,22 @@ struct DiscoveryTests {
       && record.context == MyTestContent.expectedContext
     })
   }
-#endif
 
-#if !SWT_NO_LEGACY_TEST_DISCOVERY && hasFeature(SymbolLinkageMarkers)
-  @Test("Legacy test discovery finds the same number of tests") func discoveredTestCount() async {
-    let oldFlag = Environment.variable(named: "SWT_USE_LEGACY_TEST_DISCOVERY")
-    defer {
-      Environment.setVariable(oldFlag, named: "SWT_USE_LEGACY_TEST_DISCOVERY")
+#if !SWT_NO_LEGACY_TEST_DISCOVERY
+  struct `__🟡$LegacyTestContentRecord`: __TestContentRecordContainer {
+    static var __testContentRecord: __TestContentRecord {
+      MyTestContent.record
     }
+  }
 
-    Environment.setVariable("1", named: "SWT_USE_LEGACY_TEST_DISCOVERY")
-    let testsWithOldCode = await Array(Test.all).count
-
-    Environment.setVariable("0", named: "SWT_USE_LEGACY_TEST_DISCOVERY")
-    let testsWithNewCode = await Array(Test.all).count
-
-    #expect(testsWithOldCode == testsWithNewCode)
+  @Test func legacyTestDiscovery() throws {
+    let allRecords = Array(MyTestContent.allTypeMetadataBasedTestContentRecords())
+    #expect(allRecords.count == 1)
+    let record = try #require(allRecords.first)
+    #expect(record.context == MyTestContent.expectedContext)
+    let content = try #require(record.load())
+    #expect(content.value == MyTestContent.expectedValue)
   }
 #endif
+#endif
 }