[Backtracing] Implement Codable for Backtrace.

Add support for Codable to Bactkrace.

rdar://124913332

Author: al45tair

stdlib/public/RuntimeModule/Backtrace+Codable.swift

@@ -0,0 +1,69 @@
+//===--- Backtrace+Codable.swift ------------------------------*- swift -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2023 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 the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  Defines the Codable conformance for Backtrace.
+//
+//===----------------------------------------------------------------------===//
+
+import Swift
+
+func stringFrom(sequence: some Sequence<UTF8.CodeUnit>) -> String? {
+  if #available(macOS 15.0, *) {
+    return String(validating: sequence, as: UTF8.self)
+  } else {
+    let bytes = Array(sequence)
+    return String(decoding: bytes, as: UTF8.self)
+  }
+}
+
+@available(macOS 15.0, *)
+extension Backtrace: Codable {
+
+  enum CodingKeys: CodingKey {
+    case architecture
+    case backtrace
+    case imageMap
+  }
+
+  public init(from decoder: any Decoder) throws {
+    let values = try decoder.container(keyedBy: CodingKeys.self)
+    self.architecture = try values.decode(String.self, forKey: .architecture)
+
+    let backtraceB64 = try values.decode(String.self, forKey: .backtrace)
+    self.representation = Array(Base64Decoder(source: backtraceB64.utf8))
+
+    if let imageMapB64 = try values.decodeIfPresent(String.self,
+                                                    forKey: .imageMap) {
+      self.images = ImageMap(compactImageMapData:
+                               Base64Decoder(source: imageMapB64.utf8))
+    } else {
+      self.images = nil
+    }
+  }
+
+  public func encode(to encoder: any Encoder) throws {
+    var values = encoder.container(keyedBy: CodingKeys.self)
+    try values.encode(architecture, forKey: .architecture)
+
+    let backtraceB64 = stringFrom(sequence:
+                                    Base64Encoder(source: self.representation))
+    try values.encode(backtraceB64, forKey: .backtrace)
+
+    if let imageMap = self.images {
+      let encoder = CompactImageMapFormat.Encoder(imageMap)
+      let imageMapB64 = stringFrom(sequence:
+                                     Base64Encoder(source: encoder))
+      try values.encode(imageMapB64, forKey: .imageMap)
+    }
+  }
+
+}

stdlib/public/RuntimeModule/Backtrace.swift

@@ -232,7 +232,7 @@ public struct Backtrace: CustomStringConvertible, Sendable {
   public var architecture: String
 
   /// The actual backtrace data, stored in Compact Backtrace Format.
-  private var representation: [UInt8]
+  var representation: [UInt8]
 
   /// A list of captured frame information.
   @available(macOS 10.15, *)