Store test content in a custom metadata section.

See also: swiftlang/swift#76698

Resolves #735.

Author: grynspan

Documentation/ABI/TestContent.md

@@ -21,28 +21,39 @@ the testing library are stored in dedicated platform-specific sections:
 
 | Platform | Binary Format | Section Name |
 |-|:-:|-|
-| macOS | Mach-O | `__DATA_CONST,__swift5_tests` |
-| iOS | Mach-O | `__DATA_CONST,__swift5_tests` |
-| watchOS | Mach-O | `__DATA_CONST,__swift5_tests` |
-| tvOS | Mach-O | `__DATA_CONST,__swift5_tests` |
-| visionOS | Mach-O | `__DATA_CONST,__swift5_tests` | 
-| Linux | ELF | `PT_NOTE`[^1] |
-| FreeBSD | ELF | `PT_NOTE`[^1] |
-| Android | ELF | `PT_NOTE`[^1] |
+| macOS, iOS, watchOS, tvOS, visionOS | Mach-O | `__DATA_CONST,__swift5_tests` |
+| Linux, FreeBSD, Android | ELF | `PT_NOTE`[^1] |
 | WASI | Statically Linked | `swift5_tests` |
 | Windows | PE/COFF | `.sw5test` |
 
 [^1]: On platforms that use the ELF binary format natively, test content records
       are stored in ELF program headers of type `PT_NOTE`. Take care not to
       remove these program headers (for example, by invoking [`strip(1)`](https://www.man7.org/linux/man-pages/man1/strip.1.html).)
 
-### Determining the type of test content
+### Record headers
       
 Regardless of platform, all test content records created and discoverable by the
-testing library start have the name `"Swift Testing"` stored in the implied
-`n_name` field of their underlying ELF Notes. Each record's _type_ (stored in
-the underlying ELF Note's `n_type` field) determines how the record will be
-interpreted at runtime:
+testing library have the following structure:
+
+```c
+struct SWTTestContentHeader {
+  int32_t n_namesz;
+  int32_t n_descsz;
+  int32_t n_type;
+  char n_name[n_namesz];
+  // ...
+};
+```
+
+The size of `n_name` is dynamic and cannot be statically computed. The testing
+library always generates the name `"Swift Testing"` and specifies an `n_namesz`
+value of `20` (the string being null-padded to the correct length), but other
+content may be present in the same section whose header content differs. For
+more information about this structure such as its alignment requirements, see
+the documentation for the [ELF format](https://man7.org/linux/man-pages/man5/elf.5.html).
+
+Each record's _kind_ (stored in the `n_type` field) determines how the record
+will be interpreted at runtime:
 
 | Type Value | Interpretation |
 |-:|-|
@@ -54,18 +65,28 @@ interpreted at runtime:
 <!-- When adding cases to this enumeration, be sure to also update the
 corresponding enumeration in Discovery.h and TestContentGeneration.swift. -->
 
-### Loading test content from a record
+### Record contents
 
-For all currently-defined record types, the header and name are followed by a
-structure of the following form:
+For all currently-defined record types, the header structure is immediately
+followed by the actual content of the record. A test content record currently
+contains an `accessor` function to load the corresponding Swift content and a
+`flags` field whose value depends on the type of record. The overall structure
+of a record therefore looks like:
 
 ```c
 struct SWTTestContent {
+  SWTTestContentHeader header;
   bool (* accessor)(void *);
-  uint64_t flags;
+  uint32_t flags;
+  uint32_t reserved;
 };
 ```
 
+This structure may grow in the future as needed. Check the `header.n_descsz`
+field to determine if there are additional fields present. Do not assume that
+the size of this structure will remain fixed over time or that all discovered
+test content records are the same size.
+
 #### The accessor field
 
 The function `accessor` is a C function whose signature in Swift can be restated
@@ -80,19 +101,20 @@ Swift type and returns `true`, or returns `false` if it could not generate the
 relevant content. On successful return, the caller is responsible for
 deinitializing the memory at `outValue` when done with it.
 
-The concrete Swift type of `accessor`'s result depends on the type of record:
+The concrete Swift type of the value written to `outValue` depends on the type
+of record:
 
 | Type Value | Return Type |
 |-:|-|
 | < `0` | Undefined (**do not use**) |
-| `0` ... `99` | `nil` |
+| `0` ... `99` | Reserved (**do not use**) |
 | `100` | `@Sendable () async -> Test`[^2] |
-| `101` | `ExitTest` (owned by caller) |
+| `101` | `ExitTest` (consumed by caller) |
 
 [^2]: This signature is not the signature of `accessor`, but of the Swift
-      function reference it returns. This level of indirection is necessary
-      because loading a test or suite declaration is an asynchronous operation,
-      but C functions cannot be `async`.
+      function reference it writes to `outValue`. This level of indirection is
+      necessary because loading a test or suite declaration is an asynchronous
+      operation, but C functions cannot be `async`.
 
 #### The flags field
 
@@ -105,6 +127,10 @@ For test or suite declarations (type `100`), the following flags are defined:
 
 For exit test declarations (type `101`), no flags are currently defined.
 
+#### The reserved field
+
+This field is reserved for future use. Always set it to `0`.
+
 ## Third-party test content
 
 TODO: elaborate how tools can reuse the same `n_name` and `n_type` fields to

Package.swift

@@ -164,6 +164,15 @@ extension Array where Element == PackageDescription.CXXSetting {
   static var packageSettings: Self {
     var result = Self()
 
+    result += [
+      .define("SWT_TARGET_OS_APPLE", .when(platforms: [.macOS, .iOS, .macCatalyst, .watchOS, .tvOS, .visionOS])),
+
+      .define("SWT_NO_EXIT_TESTS", .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .android])),
+      .define("SWT_NO_SNAPSHOT_TYPES", .when(platforms: [.linux, .windows, .wasi])),
+      .define("SWT_NO_DYNAMIC_LINKING", .when(platforms: [.wasi])),
+      .define("SWT_NO_PIPES", .when(platforms: [.wasi])),
+    ]
+
     // Capture the testing library's version as a C++ string constant.
     if let git = Context.gitInformation {
       let testingLibraryVersion = if let tag = git.currentTag {

Sources/Testing/CMakeLists.txt

@@ -79,6 +79,7 @@ add_library(Testing
   Test.ID.swift
   Test.swift
   Test+Discovery.swift
+  Test+Discovery+MachO.swift
   Test+Macro.swift
   Traits/Bug.swift
   Traits/Comment.swift

Sources/Testing/Test+Discovery.swift

@@ -44,7 +44,9 @@ extension Test {
         nonisolated(unsafe) let imageAddress = imageAddress
         generators.append { @Sendable in
           var result = await generator()
+#if !SWT_NO_DYNAMIC_LINKING
           result.imageAddress = imageAddress
+#endif
           return result
         }
       }
@@ -152,7 +154,7 @@ private func _enumerateTestContent(_ body: _TestContentEnumerator) {
 ///   - stop: An `inout` boolean variable indicating whether type enumeration
 ///     should stop after the function returns. Set `stop` to `true` to stop
 ///     type enumeration.
-typealias TestContentEnumerator<T> = (_ imageAddress: UnsafeRawPointer?, _ content: borrowing T, _ flags: UInt64, _ stop: inout Bool) -> Void where T: ~Copyable
+typealias TestContentEnumerator<T> = (_ imageAddress: UnsafeRawPointer?, _ content: borrowing T, _ flags: UInt32, _ stop: inout Bool) -> Void where T: ~Copyable
 
 /// Enumerate all test content known to Swift and found in the current process.
 ///

Sources/Testing/Test.swift

@@ -53,18 +53,25 @@ public struct Test: Sendable {
   /// The source location of this test.
   public var sourceLocation: SourceLocation
 
+#if !SWT_NO_DYNAMIC_LINKING
   /// The base address of the image containing this test, if available.
   ///
-  /// On platforms that do not support dynamic loading of images, the value of
-  /// this property is `nil`. Otherwise, the value is platform-specific, but
-  /// generally equal to the address of the first byte of the image mapped into
-  /// memory.
+  /// This property's value represents the image that contains this test and is
+  /// equivalent to various platform-specific values:
   ///
-  /// On Apple platforms, this property's value is equivalent to a pointer to a
-  /// `mach_header` value. On Windows, it is equivalent to an `HMODULE`. It is
-  /// never equivalent to the pointer returned from a call to `dlopen()` (on
-  /// platforms that have that function.)
-  nonisolated(unsafe) var imageAddress: UnsafeRawPointer?
+  /// | Platform | Equivalent To |
+  /// |-|-|
+  /// | macOS, iOS, tvOS, visionOS | `UnsafePointer<mach_header_64>` |
+  /// | watchOS | `UnsafePointer<mach_header>` |
+  /// | Linux, FreeBSD, Android (32-bit) | `UnsafePointer<Elf32_Ehdr>` |
+  /// | Linux, FreeBSD, Android (64-bit) | `UnsafePointer<Elf64_Ehdr>` |
+  /// | Windows | `HMODULE` |
+  ///
+  /// The value of this property is distinct from the pointer returned by
+  /// `dlopen()` (on platforms that have that function.)
+  @_spi(ForToolsIntegrationOnly)
+  public nonisolated(unsafe) var imageAddress: UnsafeRawPointer?
+#endif
 
   /// Information about the type containing this test, if any.
   ///

Sources/TestingMacros/Support/TestContentGeneration.swift

@@ -107,14 +107,16 @@ func makeTestContentRecordDecl(named name: TokenSyntax, in typeName: TypeSyntax?
     type: Int32,
     name: \(elfNoteName.type),
     accessor: @convention(c) (UnsafeMutableRawPointer) -> Bool,
-    flags: UInt64
+    flags: UInt32,
+    reserved: UInt32
   ) = (
     Int32(MemoryLayout<\(elfNoteName.type)>.stride),
-    Int32(MemoryLayout<UnsafeRawPointer>.stride + MemoryLayout<UInt64>.stride),
+    Int32(MemoryLayout<UnsafeRawPointer>.stride + MemoryLayout<UInt32>.stride + MemoryLayout<UInt32>.stride),
     \(raw: kind.rawValue) as Int32,
     \(elfNoteName.expression) as \(elfNoteName.type),
     \(accessorName) as @convention(c) (UnsafeMutableRawPointer) -> Bool,
-    \(raw: flags) as UInt64
+    \(raw: flags) as UInt32,
+    0 as UInt32
   )
   """
 }

Sources/_TestingInternals/Discovery.cpp

@@ -414,7 +414,8 @@ void swt_enumerateTestContent(void *context, SWTTestContentEnumerator body) {
       // Extract the content of this record now that we know it's ours.
       struct Content {
         bool (* accessor)(void *outValue);
-        uint64_t flags;
+        uint32_t flags;
+        uint32_t reserved;
       };
       auto content = reinterpret_cast<const Content *>(record.getDescription());
       if (!content) {

Sources/_TestingInternals/include/Discovery.h

@@ -54,7 +54,7 @@ typedef struct SWTTestContentRecord {
   ///
   /// The value of this property is dependent on the kind of test content this
   /// instance represents.
-  uint64_t flags;
+  uint32_t flags;
 } SWTTestContentRecord;
 
 /// The type of callback called by `swt_enumerateTestContent()`.