Empty codingkey encode decode output (#267)

* Fix encoding output when CodingKey is empty

* Fix decoding when CodingKey is empty

* Simplified and improved Choice decoding

Author: Alkenso

README.md

@@ -226,8 +226,8 @@ set a property `removeWhitespaceElements` to `true` (the default value is `false
 
 Starting with [version 0.8](https://github.com/CoreOffice/XMLCoder/releases/tag/0.8.0),
 you can encode and decode `enum`s with associated values by conforming your
-`CodingKey` type additionally to `XMLChoiceCodingKey`. This allows decoding
-XML elements similar in structure to this example:
+`CodingKey` type additionally to `XMLChoiceCodingKey`. This allows encoding 
+and decoding XML elements similar in structure to this example:
 
 ```xml
 <container>
@@ -242,41 +242,76 @@ XML elements similar in structure to this example:
 To decode these elements you can use this type:
 
 ```swift
-enum IntOrString: Equatable {
+enum IntOrString: Codable {
     case int(Int)
     case string(String)
-}
-
-extension IntOrString: Codable {
+    
     enum CodingKeys: String, XMLChoiceCodingKey {
         case int
         case string
     }
+    
+    enum IntCodingKeys: String, CodingKey { case _0 = "" }
+    enum StringCodingKeys: String, CodingKey { case _0 = "" }
+}
+```
+
+This is described in more details in PR [\#119](https://github.com/CoreOffice/XMLCoder/pull/119)
+by [@jsbean](https://github.com/jsbean) and [@bwetherfield](https://github.com/bwetherfield).
+
+#### Choice elements with (inlined) complex associated values
+
+Lets extend previous example replacing simple types with complex 
+in assosiated values. This example would cover XML like:
+
+```xml
+<container>
+    <nested attr="n1_a1">
+        <val>n1_v1</val>
+        <labeled>
+            <val>n2_val</val>
+        </labeled>
+    </nested>
+    <simple attr="n1_a1">
+        <val>n1_v1</val>
+    </simple>
+</container>
+```
 
-    func encode(to encoder: Encoder) throws {
-        var container = encoder.container(keyedBy: CodingKeys.self)
-        switch self {
-        case let .int(value):
-            try container.encode(value, forKey: .int)
-        case let .string(value):
-            try container.encode(value, forKey: .string)
+```swift
+enum InlineChoice: Equatable, Codable {
+    case simple(Nested1)
+    case nested(Nested1, labeled: Nested2)
+    
+    enum CodingKeys: String, CodingKey, XMLChoiceCodingKey {
+        case simple, nested
+    }
+    
+    enum SimpleCodingKeys: String, CodingKey { case _0 = "" }
+    
+    enum NestedCodingKeys: String, CodingKey {
+        case _0 = ""
+        case labeled
+    }
+    
+    struct Nested1: Equatable, Codable, DynamicNodeEncoding {
+        var attr = "n1_a1"
+        var val = "n1_v1"
+        
+        public static func nodeEncoding(for key: CodingKey) -> XMLEncoder.NodeEncoding {
+            switch key {
+            case CodingKeys.attr: return .attribute
+            default: return .element
+            }
         }
     }
 
-    init(from decoder: Decoder) throws {
-        let container = try decoder.container(keyedBy: CodingKeys.self)
-        do {
-            self = .int(try container.decode(Int.self, forKey: .int))
-        } catch {
-            self = .string(try container.decode(String.self, forKey: .string))
-        }
+    struct Nested2: Equatable, Codable {
+        var val = "n2_val"
     }
 }
 ```
 
-This is described in more details in PR [\#119](https://github.com/CoreOffice/XMLCoder/pull/119)
-by [@jsbean](https://github.com/jsbean) and [@bwetherfield](https://github.com/bwetherfield).
-
 ### Integrating with [Combine](https://developer.apple.com/documentation/combine)
 
 Starting with XMLCoder [version 0.9](https://github.com/CoreOffice/XMLCoder/releases/tag/0.9.0),

Sources/XMLCoder/Auxiliaries/Utils.swift

@@ -0,0 +1,13 @@
+// Copyright (c) 2018-2023 XMLCoder contributors
+//
+// This software is released under the MIT License.
+// https://opensource.org/licenses/MIT
+//
+//  Created by Alkenso (Vladimir Vashurkin) on 08.06.2023.
+//
+
+import Foundation
+
+extension CodingKey {
+    internal var isInlined: Bool { stringValue == "" }
+}

Sources/XMLCoder/Auxiliaries/XMLCoderElement.swift

@@ -32,6 +32,10 @@ struct XMLCoderElement: Equatable {
         return isStringNode || isCDATANode
     }
 
+    private var isInlined: Bool {
+        return key.isEmpty
+    }
+
     init(
         key: String,
         elements: [XMLCoderElement] = [],
@@ -193,8 +197,9 @@ struct XMLCoderElement: Equatable {
         }
 
         var string = ""
-        string += element._toXMLString(indented: level + 1, escapedCharacters, formatting, indentation)
-        string += prettyPrinted ? "\n" : ""
+        let indentLevel = isInlined ? level : level + 1
+        string += element._toXMLString(indented: indentLevel, escapedCharacters, formatting, indentation)
+        string += prettyPrinted && !isInlined ? "\n" : ""
         return string
     }
 
@@ -294,9 +299,9 @@ struct XMLCoderElement: Equatable {
         let prettyPrinted = formatting.contains(.prettyPrinted)
         let prefix: String
         switch indentation {
-        case let .spaces(count) where prettyPrinted:
+        case let .spaces(count) where prettyPrinted && !isInlined:
             prefix = String(repeating: " ", count: level * count)
-        case let .tabs(count) where prettyPrinted:
+        case let .tabs(count) where prettyPrinted && !isInlined:
             prefix = String(repeating: "\t", count: level * count)
         default:
             prefix = ""

Sources/XMLCoder/Decoder/XMLChoiceDecodingContainer.swift

@@ -59,11 +59,24 @@ struct XMLChoiceDecodingContainer<K: CodingKey>: KeyedDecodingContainerProtocol
     public func nestedContainer<NestedKey>(
         keyedBy _: NestedKey.Type, forKey key: Key
     ) throws -> KeyedDecodingContainer<NestedKey> {
-        throw DecodingError.typeMismatch(
-            at: codingPath,
-            expectation: NestedKey.self,
-            reality: container
-        )
+        guard container.unboxed.key == key.stringValue else {
+            throw DecodingError.typeMismatch(
+                at: codingPath,
+                expectation: NestedKey.self,
+                reality: container
+            )
+        }
+        
+        let value = container.unboxed.element
+        guard let container = XMLKeyedDecodingContainer<NestedKey>(box: value, decoder: decoder) else {
+            throw DecodingError.typeMismatch(
+                at: codingPath,
+                expectation: [String: Any].self,
+                reality: value
+            )
+        }
+        
+        return KeyedDecodingContainer(container)
     }
 
     public func nestedUnkeyedContainer(forKey key: Key) throws -> UnkeyedDecodingContainer {

Sources/XMLCoder/Decoder/XMLKeyedDecodingContainer.swift

@@ -133,25 +133,7 @@ struct XMLKeyedDecodingContainer<K: CodingKey>: KeyedDecodingContainerProtocol {
             ))
         }
 
-        let container: XMLKeyedDecodingContainer<NestedKey>
-        if let keyedContainer = value as? KeyedContainer {
-            container = XMLKeyedDecodingContainer<NestedKey>(
-                referencing: decoder,
-                wrapping: keyedContainer
-            )
-        } else if let keyedContainer = value as? KeyedBox {
-            container = XMLKeyedDecodingContainer<NestedKey>(
-                referencing: decoder,
-                wrapping: SharedBox(keyedContainer)
-            )
-        } else if let singleBox = value as? SingleKeyedBox {
-            let element = (singleBox.key, singleBox.element)
-            let keyedContainer = KeyedBox(elements: [element], attributes: [])
-            container = XMLKeyedDecodingContainer<NestedKey>(
-                referencing: decoder,
-                wrapping: SharedBox(keyedContainer)
-            )
-        } else {
+        guard let container = XMLKeyedDecodingContainer<NestedKey>(box: value, decoder: decoder) else {
             throw DecodingError.typeMismatch(
                 at: codingPath,
                 expectation: [String: Any].self,
@@ -192,6 +174,32 @@ struct XMLKeyedDecodingContainer<K: CodingKey>: KeyedDecodingContainerProtocol {
     }
 }
 
+extension XMLKeyedDecodingContainer {
+    internal init?(box: Box, decoder: XMLDecoderImplementation) {
+        switch box {
+        case let keyedContainer as KeyedContainer:
+            self.init(
+                referencing: decoder,
+                wrapping: keyedContainer
+            )
+        case let keyedBox as KeyedBox:
+            self.init(
+                referencing: decoder,
+                wrapping: SharedBox(keyedBox)
+            )
+        case let singleBox as SingleKeyedBox:
+            let element = (singleBox.key, singleBox.element)
+            let keyedContainer = KeyedBox(elements: [element], attributes: [])
+            self.init(
+                referencing: decoder,
+                wrapping: SharedBox(keyedContainer)
+            )
+        default:
+            return nil
+        }
+    }
+}
+
 /// Private functions
 extension XMLKeyedDecodingContainer {
     private func _errorDescription(of key: CodingKey) -> String {
@@ -248,7 +256,7 @@ extension XMLKeyedDecodingContainer {
 
         let elements = container
             .withShared { keyedBox -> [KeyedBox.Element] in
-                keyedBox.elements[key.stringValue].map {
+                return (key.isInlined ? keyedBox.elements.values : keyedBox.elements[key.stringValue]).map {
                     if let singleKeyed = $0 as? SingleKeyedBox {
                         return singleKeyed.element.isNull ? singleKeyed : singleKeyed.element
                     } else {
@@ -258,7 +266,7 @@ extension XMLKeyedDecodingContainer {
             }
 
         let attributes = container.withShared { keyedBox in
-            keyedBox.attributes[key.stringValue]
+            key.isInlined ? keyedBox.attributes.values : keyedBox.attributes[key.stringValue]
         }
 
         decoder.codingPath.append(key)
@@ -271,7 +279,6 @@ extension XMLKeyedDecodingContainer {
             _ = decoder.nodeDecodings.removeLast()
             decoder.codingPath.removeLast()
         }
-        let box: Box
 
         // You can't decode sequences from attributes, but other strategies
         // need special handling for empty sequences.
@@ -292,21 +299,26 @@ extension XMLKeyedDecodingContainer {
             return ((cdata as? StringBox)?.unboxed as? T) ?? emptyString
         }
 
-        switch strategy(key) {
-        case .attribute?:
-            box = try getAttributeBox(for: type, attributes, key)
-        case .element?:
-            box = try getElementBox(for: type, elements, key)
-        case .elementOrAttribute?:
-            box = try getAttributeOrElementBox(attributes, elements, key)
-        default:
-            switch type {
-            case is XMLAttributeProtocol.Type:
+        let box: Box
+        if key.isInlined {
+            box = container.typeErasedUnbox()
+        } else {
+            switch strategy(key) {
+            case .attribute?:
                 box = try getAttributeBox(for: type, attributes, key)
-            case is XMLElementProtocol.Type:
+            case .element?:
                 box = try getElementBox(for: type, elements, key)
-            default:
+            case .elementOrAttribute?:
                 box = try getAttributeOrElementBox(attributes, elements, key)
+            default:
+                switch type {
+                case is XMLAttributeProtocol.Type:
+                    box = try getAttributeBox(for: type, attributes, key)
+                case is XMLElementProtocol.Type:
+                    box = try getElementBox(for: type, elements, key)
+                default:
+                    box = try getAttributeOrElementBox(attributes, elements, key)
+                }
             }
         }