Add Codable support

.gitattributes

@@ -0,0 +1 @@
+*.swift.gyb linguist-language=Swift

.github/workflows/tests.yml

@@ -114,3 +114,17 @@ jobs:
 
       - name: swift test
         run: swift test
+
+  check-gyb-run:
+    name: Check GYB has been run
+    runs-on: macOS-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install GYB
+        run: brew install nshipster/formulae/gyb
+
+      - run: ./scripts/generate-KeyPathCodingKeyCollectionBuilder.sh
+
+      - name: Check GYB was run before commit
+        run: git diff --exit-code

Package.swift

@@ -14,8 +14,15 @@ let package = Package(
         .package(url: "https://github.com/Quick/Nimble.git", from: "8.0.0"),
     ],
     targets: [
-        .target(name: "Partial"),
-        .testTarget(name: "PartialTests", dependencies: ["Partial", "Quick", "Nimble"]),
+        .target(name: "Partial", exclude: ["Codable/KeyPathCodingKeyCollectionBuilder.swift.gyb"]),
+        .testTarget(
+            name: "PartialTests",
+            dependencies: ["Partial", "Quick", "Nimble"],
+            exclude: [
+                "Tests/Partial+CodableTests.swift.gyb",
+                "Tests/PartialBuilder+CodableTests.swift.gyb",
+            ]
+        ),
     ],
     swiftLanguageVersions: [.v5]
 )

Package@swift-5.2.swift

@@ -14,8 +14,15 @@ let package = Package(
         .package(url: "https://github.com/Quick/Nimble.git", from: "8.0.0"),
     ],
     targets: [
-        .target(name: "Partial"),
-        .testTarget(name: "PartialTests", dependencies: ["Partial", "Quick", "Nimble"]),
+        .target(name: "Partial", exclude: ["Codable/KeyPathCodingKeyCollectionBuilder.swift.gyb"]),
+        .testTarget(
+            name: "PartialTests",
+            dependencies: ["Partial", "Quick", "Nimble"],
+            exclude: [
+                "Tests/Partial+CodableTests.swift.gyb",
+                "Tests/PartialBuilder+CodableTests.swift.gyb",
+            ]
+        ),
     ],
     swiftLanguageVersions: [.v5]
 )

Package@swift-5.3.swift

@@ -18,8 +18,15 @@ let package = Package(
         .package(url: "https://github.com/Realm/SwiftLint", from: "0.32.0"),
     ],
     targets: [
-        .target(name: "Partial"),
-        .testTarget(name: "PartialTests", dependencies: ["Partial", "Quick", "Nimble"]),
+        .target(name: "Partial", exclude: ["Codable/KeyPathCodingKeyCollectionBuilder.swift.gyb"]),
+        .testTarget(
+            name: "PartialTests",
+            dependencies: ["Partial", "Quick", "Nimble"],
+            exclude: [
+                "Tests/Partial+CodableTests.swift.gyb",
+                "Tests/PartialBuilder+CodableTests.swift.gyb",
+            ]
+        ),
         .target(
             name: "DangerDependencies",
             dependencies: [

Partial.podspec

@@ -10,7 +10,7 @@ Pod::Spec.new do |spec|
     :git => "https://github.com/JosephDuffy/Partial.git",
     :tag => "v#{spec.version}"
   }
-  spec.source_files = "Sources/Partial/*.swift"
+  spec.source_files = "Sources/Partial/**/*.swift"
   spec.osx.deployment_target = "10.10"
   spec.ios.deployment_target = "8.0"
   spec.tvos.deployment_target = "9.0"

Sources/Partial/Codable/KeyPathCodingKeyCollection.swift

@@ -0,0 +1,37 @@
+public struct KeyPathCodingKeyCollection<Root, CodingKey: Swift.CodingKey & Hashable> {
+    public enum EncodeError: Error {
+        case invalidType(value: Any, expectedType: Any.Type)
+    }
+
+    private typealias Encoder = (_ value: Any, _ container: inout KeyedEncodingContainer<CodingKey>) throws -> Void
+    private typealias Decoder = (_ codingKey: CodingKey, _ container: KeyedDecodingContainer<CodingKey>) throws -> (Any, PartialKeyPath<Root>)?
+
+    private var encoders: [PartialKeyPath<Root>: Encoder] = [:]
+    private var decoders: [CodingKey: Decoder] = [:]
+
+    func encode(_ value: Any, forKey keyPath: PartialKeyPath<Root>, to container: inout KeyedEncodingContainer<CodingKey>) throws {
+        try encoders[keyPath]?(value, &container)
+    }
+
+    func decode(_ codingKey: CodingKey, in container: KeyedDecodingContainer<CodingKey>) throws -> (Any, PartialKeyPath<Root>)? {
+        return try decoders[codingKey]?(codingKey, container)
+    }
+
+    public mutating func addPair<Value: Swift.Codable>(keyPath: KeyPath<Root, Value>, codingKey: CodingKey) {
+        encoders[keyPath] = { value, container in
+            guard let caseValue = value as? Value else {
+                throw EncodeError.invalidType(value: value, expectedType: Value.self)
+            }
+
+            try container.encode(caseValue, forKey: codingKey)
+        }
+
+        decoders[codingKey] = { codingKey, container in
+            if let decodedValue = try container.decodeIfPresent(Value.self, forKey: codingKey) {
+                return (decodedValue, keyPath)
+            } else {
+                return nil
+            }
+        }
+    }
+}