Copyable snapshots

Sources/DebugSnapshots/DebugSnapshotConvertible.swift

@@ -3,7 +3,7 @@
 /// This conformance is automatically applied to a type using the ``DebugSnapshot(_:)`` macro.
 public protocol DebugSnapshotConvertible<DebugSnapshot> {
   /// A type representing a "snapshot" of this type.
-  associatedtype DebugSnapshot
+  associatedtype DebugSnapshot: DebugSnapshotConvertible<DebugSnapshot>
 
   static func _debugSnapshot(_ value: Self, visitor: inout _DebugSnapshotVisitor) -> DebugSnapshot
 }
@@ -13,12 +13,7 @@ extension Array: DebugSnapshotConvertible where Element: DebugSnapshotConvertibl
     _ value: Self,
     visitor: inout _DebugSnapshotVisitor
   ) -> [Element.DebugSnapshot] {
-    var result: [Element.DebugSnapshot] = []
-    result.reserveCapacity(value.count)
-    for element in value {
-      result.append(Element._debugSnapshot(element, visitor: &visitor))
-    }
-    return result
+    value.map { Element._debugSnapshot($0, visitor: &visitor) }
   }
 }
 
@@ -27,12 +22,7 @@ extension Dictionary: DebugSnapshotConvertible where Value: DebugSnapshotConvert
     _ value: Self,
     visitor: inout _DebugSnapshotVisitor
   ) -> [Key: Value.DebugSnapshot] {
-    var result: [Key: Value.DebugSnapshot] = [:]
-    result.reserveCapacity(value.count)
-    for (key, value) in value {
-      result[key] = Value._debugSnapshot(value, visitor: &visitor)
-    }
-    return result
+    value.mapValues { Value._debugSnapshot($0, visitor: &visitor) }
   }
 }
 
@@ -41,12 +31,7 @@ extension Optional: DebugSnapshotConvertible where Wrapped: DebugSnapshotConvert
     _ value: Self,
     visitor: inout _DebugSnapshotVisitor
   ) -> Wrapped.DebugSnapshot? {
-    switch value {
-    case .none:
-      return nil
-    case .some(let wrapped):
-      return Wrapped._debugSnapshot(wrapped, visitor: &visitor)
-    }
+    value.map { Wrapped._debugSnapshot($0, visitor: &visitor) }
   }
 }
 

Sources/DebugSnapshotsMacrosSupport/DebugSnapshotMacro.swift

@@ -258,6 +258,7 @@ private func structMemberDeclarations(
   if hasIndirectProperties {
     allConformances.append("CustomReflectable")
   }
+  allConformances.append("\(moduleName).DebugSnapshotConvertible")
   let conformancesDescription =
     snapshotConformanceDescription(allConformances)
   let customMirrorDecl: String
@@ -274,12 +275,28 @@ private func structMemberDeclarations(
   } else {
     customMirrorDecl = ""
   }
+  let convertibleSnapshotAssignments =
+    properties
+    .filter { $0.isDebugSnapshotConvertible }
+    .map {
+      "snapshot.\($0.name) = \(moduleName)._debugSnapshot(value.\($0.name), visitor: &visitor)"
+    }
+  let snapshotBody =
+    convertibleSnapshotAssignments.isEmpty
+    ? "value"
+    : "var snapshot = value\n\(convertibleSnapshotAssignments.joined(separator: "\n"))\nreturn snapshot"
   let representation =
     DeclSyntax(
       """
       \(raw: propagatedAttributes.description)\
       public struct DebugSnapshot\(raw: conformancesDescription) {
       \(raw: propertyLines.joined(separator: "\n"))\(raw: customMirrorDecl)
+      public static func _debugSnapshot(\
+      _ value: DebugSnapshot, \
+      visitor: inout \(raw: moduleName)._DebugSnapshotVisitor\
+      ) -> DebugSnapshot {
+      \(raw: snapshotBody)
+      }
       }
       """
     )
@@ -345,25 +362,48 @@ private func classMemberDeclarations(
 
   let initParams = classInitParams(for: properties, modelName: modelDecl.name)
   let snapshotInitArguments = properties.map { "\($0.name): \($0.name)" }.joined(separator: ", ")
+
+  let convertibleSnapshotAssignments =
+    properties
+    .filter { $0.isDebugSnapshotConvertible }
+    .map {
+      "snapshot.\($0.name) = \(moduleName)._debugSnapshot(value.\($0.name), visitor: &visitor)"
+    }
+  let convertibleSnapshotAssignmentsCode =
+    convertibleSnapshotAssignments.isEmpty
+    ? ""
+    : "\n" + convertibleSnapshotAssignments.joined(separator: "\n")
+
+  let nonConvertibleInitArguments =
+    properties
+    .filter { !$0.isDebugSnapshotConvertible }
+    .map { "\($0.name): value.\($0.name)" }
+    .joined(separator: ", ")
   let debugSnapshotClass =
     DeclSyntax(
       """
-      public final class DebugSnapshot: \(raw: moduleName)._DebugSnapshotObject {
+      public final class DebugSnapshot: \
+      \(raw: moduleName)._DebugSnapshotObject, \(raw: moduleName).DebugSnapshotConvertible {
       public var _snapshot: DebugSnapshotValue
       public var _originIdentifier: ObjectIdentifier?
       public var _diffSnapshot: (any \(raw: moduleName)._DebugSnapshotObject)?
       public init(\(raw: initParams)) {
       self._snapshot = DebugSnapshotValue(\(raw: snapshotInitArguments))
       }
+      public static func _debugSnapshot(\
+      _ value: DebugSnapshot, \
+      visitor: inout \(raw: moduleName)._DebugSnapshotVisitor\
+      ) -> DebugSnapshot {
+      if let existing: DebugSnapshot = visitor.lookup(value) { return existing }
+      let snapshot = DebugSnapshot(\(raw: nonConvertibleInitArguments))
+      snapshot._originIdentifier = value._originIdentifier
+      visitor.register(value, snapshot: snapshot)\(raw: convertibleSnapshotAssignmentsCode)
+      return snapshot
+      }
       }
       """
     )
 
-  let nonConvertibleInitArguments =
-    properties
-    .filter { !$0.isDebugSnapshotConvertible }
-    .map { "\($0.name): value.\($0.name)" }
-    .joined(separator: ", ")
   let convertibleAssignments =
     properties
     .filter { $0.isDebugSnapshotConvertible }
@@ -555,17 +595,26 @@ private func enumMemberDeclarations(
     debugSnapshotConformances(
       for: declaration,
       properties: []
-    ) + propagatedAttributes.conformances
+    ) + propagatedAttributes.conformances + ["\(moduleName).DebugSnapshotConvertible"]
   )
   let conformanceDescription =
     snapshotConformanceDescription(debugSnapshotConformances)
   let snapshotCaseLines = enumCases.map { debugSnapshotCaseDeclaration($0, modelName: name) }
+  let snapshotSwitchCases = enumCases.map(snapshotSwitchCase)
   let representation =
     DeclSyntax(
       """
       \(raw: propagatedAttributes.description)\
       public \(raw: isIndirect ? "indirect " : "")enum DebugSnapshot\(raw: conformanceDescription) {
       \(raw: snapshotCaseLines.joined(separator: "\n"))
+      public static func _debugSnapshot(\
+      _ value: DebugSnapshot, \
+      visitor: inout \(raw: moduleName)._DebugSnapshotVisitor\
+      ) -> DebugSnapshot {
+      switch value {
+      \(raw: snapshotSwitchCases.joined(separator: "\n"))
+      }
+      }
       }
       """
     )
@@ -657,6 +706,34 @@ private func debugSnapshotSwitchCase(_ enumCase: ModelDecl.EnumCase) -> String {
     """
 }
 
+private func snapshotSwitchCase(_ enumCase: ModelDecl.EnumCase) -> String {
+  let name = enumCase.element.name.text
+  let parameters = Array(enumCase.element.parameterClause?.parameters ?? [])
+  let bindings = parameters.indices.map { "v\($0 + 1)" }
+
+  if enumCase.isIgnored || bindings.isEmpty {
+    return """
+      case .\(name):
+        return .\(name)
+      """
+  }
+
+  let pattern = ".\(name)(\(bindings.map { "let \($0)" }.joined(separator: ", ")))"
+  let valueArguments = zip(parameters, bindings)
+    .map { parameter, binding in
+      let mappedValue =
+        enumCase.isDebugSnapshotConvertible
+        ? "\(moduleName)._debugSnapshot(\(binding), visitor: &visitor)"
+        : binding
+      return "\(caseParameterLabelPrefix(parameter))\(mappedValue)"
+    }
+    .joined(separator: ", ")
+  return """
+    case \(pattern):
+      return .\(name)(\(valueArguments))
+    """
+}
+
 private func debugSnapshotType(_ type: TypeSyntax) -> TypeSyntax {
   if let optionalType = type.trimmed.as(OptionalTypeSyntax.self) {
     return TypeSyntax(