[WIP] Attachment.bytes property

Sources/Testing/ABI/Encoded/ABI.EncodedAttachment.swift

@@ -103,10 +103,6 @@ extension ABI.EncodedAttachment: Attachable {
     _bytes?.rawValue.count
   }
 
-  /// An error type that is thrown when ``ABI/EncodedAttachment`` cannot satisfy
-  /// a request for the underlying attachment's bytes.
-  fileprivate struct BytesUnavailableError: Error {}
-
   borrowing func withUnsafeBytes<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
     if let bytes = _bytes?.rawValue {
       return try bytes.withUnsafeBytes(body)
@@ -135,9 +131,3 @@ extension ABI.EncodedAttachment: Attachable {
     _preferredName ?? suggestedName
   }
 }
-
-extension ABI.EncodedAttachment.BytesUnavailableError: CustomStringConvertible {
-  var description: String {
-    "The attachment's content could not be deserialized."
-  }
-}

Sources/Testing/Attachments/Attachable.swift

@@ -80,6 +80,9 @@ public protocol Attachable: ~Copyable {
   /// }
   borrowing func withUnsafeBytes<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R
 
+  @_lifetime(borrow self)
+  borrowing func bytes(for attachment: borrowing Attachment<Self>) throws -> RawSpan
+
   /// Generate a preferred name for the given attachment.
   ///
   /// - Parameters:
@@ -101,6 +104,18 @@ public protocol Attachable: ~Copyable {
   borrowing func preferredName(for attachment: borrowing Attachment<Self>, basedOn suggestedName: String) -> String
 }
 
+// MARK: -
+
+/// An error type that is thrown when the testing library cannot satisfy a
+/// request for an attachment's bytes.
+struct BytesUnavailableError: Error {}
+
+extension BytesUnavailableError: CustomStringConvertible {
+  var description: String {
+    "The attachment's content could not be deserialized."
+  }
+}
+
 // MARK: - Default implementations
 
 /// @Metadata {
@@ -123,6 +138,11 @@ extension Attachable where Self: ~Copyable {
   public borrowing func preferredName(for attachment: borrowing Attachment<Self>, basedOn suggestedName: String) -> String {
     suggestedName
   }
+
+  @_lifetime(borrow self)
+  public borrowing func bytes(for attachment: borrowing Attachment<Self>) throws -> RawSpan {
+    throw BytesUnavailableError()
+  }
 }
 
 /// @Metadata {
@@ -202,6 +222,11 @@ extension ContiguousArray<UInt8>: Attachable {
   public func withUnsafeBytes<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
     try withUnsafeBytes(body)
   }
+
+  @_lifetime(borrow self)
+  public borrowing func bytes(for attachment: borrowing Attachment<Self>) throws -> RawSpan {
+    span.bytes
+  }
 }
 
 /// @Metadata {
@@ -216,6 +241,11 @@ extension ArraySlice<UInt8>: Attachable {
   public func withUnsafeBytes<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
     try withUnsafeBytes(body)
   }
+
+  @_lifetime(borrow self)
+  public borrowing func bytes(for attachment: borrowing Attachment<Self>) throws -> RawSpan {
+    span.bytes
+  }
 }
 
 /// @Metadata {

Sources/Testing/Attachments/Attachment.swift

@@ -366,6 +366,20 @@ extension Attachment where AttachableValue: ~Copyable {
   @inlinable public borrowing func withUnsafeBytes<R>(_ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
     try attachableValue.withUnsafeBytes(for: self, body)
   }
+
+  @_lifetime(borrow self)
+  private func _makeBytes(from attachableValue: borrowing AttachableValue) throws -> RawSpan {
+    let result = try attachableValue.bytes(for: self)
+    return _overrideLifetime(result, copying: self)
+  }
+
+  @_spi(Experimental)
+  public var bytes: RawSpan {
+    @_lifetime(borrow self)
+    borrowing get throws {
+      try _makeBytes(from: _storage.value)
+    }
+  }
 }
 
 #if !SWT_NO_FILE_IO