Correctly handle Pkl classes and typealiases during codegen and decoding

Author: HT154

Package.swift

@@ -92,6 +92,7 @@ let package = Package(
                 "Fixtures/Collections.pkl",
                 "Fixtures/Poly.pkl",
                 "Fixtures/ApiTypes.pkl",
+                "Fixtures/Collections2.pkl",
             ],
             swiftSettings: [.enableUpcomingFeature("StrictConcurrency")]
         ),

Sources/PklSwift/API/PklClass.swift

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+public struct PklClass: Hashable {}
+
+extension PklClass: PklSerializableType, Sendable {
+    public static let messageTag: PklValueType = .class
+
+    public init(from decoder: Decoder) throws {}
+}

Sources/PklSwift/API/PklTypeAlias.swift

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+public struct PklTypeAlias: Hashable {}
+
+extension PklTypeAlias: PklSerializableType, Sendable {
+    public static let messageTag: PklValueType = .typealias
+
+    public init(from decoder: Decoder) throws {}
+}

Sources/PklSwift/Decoder/PklDecoder.swift

@@ -18,21 +18,21 @@ import Foundation
 import MessagePack
 
 public enum PklValueType: UInt8, Decodable, Sendable {
-    case object = 0x1
-    case map = 0x2
-    case mapping = 0x3
-    case list = 0x4
-    case listing = 0x5
-    case set = 0x6
-    case duration = 0x7
-    case dataSize = 0x8
-    case pair = 0x9
-    case intSeq = 0xA
-    case regex = 0xB
-    case `class` = 0xC
-    case `typealias` = 0xD
-    case function = 0xE
-    case bytes = 0xF
+    case object = 0x01
+    case map = 0x02
+    case mapping = 0x03
+    case list = 0x04
+    case listing = 0x05
+    case set = 0x06
+    case duration = 0x07
+    case dataSize = 0x08
+    case pair = 0x09
+    case intSeq = 0x0A
+    case regex = 0x0B
+    case `class` = 0x0C
+    case `typealias` = 0x0D
+    case function = 0x0E
+    case bytes = 0x0F
     case objectMemberProperty = 0x10
     case objectMemberEntry = 0x11
     case objectMemberElement = 0x12
@@ -237,6 +237,12 @@ extension _PklDecoder {
             case .dataSize:
                 let decoder = try _PklDecoder(value: propertyValue)
                 return try PklAny(value: DataSize(from: decoder))
+            case .class:
+                let decoder = try _PklDecoder(value: propertyValue)
+                return try PklAny(value: PklClass(from: decoder))
+            case .typealias:
+                let decoder = try _PklDecoder(value: propertyValue)
+                return try PklAny(value: PklTypeAlias(from: decoder))
             case .bytes:
                 guard case .bin(let bytes) = value[1] else {
                     throw DecodingError.dataCorrupted(

Sources/pkl-gen-swift/PklGenSwift.swift

@@ -182,7 +182,8 @@ struct PklGenSwift: AsyncParsableCommand {
             )
             try await cmd.run()
         } catch let error as PklError {
-            Self.exit(withError: error)
+            FileHandle.standardError.write(Data(error.message.utf8))
+            Self.exit()
         }
     }
 }

Tests/PklSwiftTests/Fixtures/ApiTypes.pkl

@@ -1,2 +1,8 @@
 res1: Duration = 10.h
-res2: DataSize = 1.2345.gib
+res2: DataSize = 1.2345.gib
+
+stringClass: Class = String
+moduleClass: Class = module.getClass()
+typeAlias: TypeAlias = Foo
+
+typealias Foo = String

Tests/PklSwiftTests/Fixtures/Generated/ApiTypes.pkl.swift

@@ -11,12 +11,29 @@ extension ApiTypes {
 
         public var res2: DataSize
 
-        public init(res1: Duration, res2: DataSize) {
+        public var stringClass: PklClass
+
+        public var moduleClass: PklClass
+
+        public var typeAlias: PklTypeAlias
+
+        public init(
+            res1: Duration,
+            res2: DataSize,
+            stringClass: PklClass,
+            moduleClass: PklClass,
+            typeAlias: PklTypeAlias
+        ) {
             self.res1 = res1
             self.res2 = res2
+            self.stringClass = stringClass
+            self.moduleClass = moduleClass
+            self.typeAlias = typeAlias
         }
     }
 
+    public typealias Foo = String
+
     /// Load the Pkl module at the given source and evaluate it into `ApiTypes.Module`.
     ///
     /// - Parameter source: The source of the Pkl module.

Tests/PklSwiftTests/FixturesTest.swift

@@ -94,7 +94,10 @@ class FixturesTest: XCTestCase {
             result,
             ApiTypes.Module(
                 res1: .hours(10),
-                res2: .gibibytes(1.2345)
+                res2: .gibibytes(1.2345),
+                stringClass: PklClass(),
+                moduleClass: PklClass(),
+                typeAlias: PklTypeAlias()
             )
         )
     }

codegen/snippet-tests/input/Classes.pkl

@@ -15,12 +15,105 @@
 // ===----------------------------------------------------------------------===//
 module Classes
 
-animals: Listing<Animal> = new {
-  new { name = "Uni" }
-  new { name = "Wally" }
-  new { name = "Mouse" }
+bug: Bug
+
+蚊子: Bug
+
+thisPerson: ThisPerson
+
+d: D
+
+hidden myHiddenProp: String
+
+class Wheel {
+  hasSpokes: Boolean
+}
+
+class Bike {
+  isFixie: Boolean
+
+  /// Wheels are the front and back wheels.
+  ///
+  /// There are typically two of them.
+  wheels: List<Wheel>
+}
+
+abstract class Being {
+  isAlive: Boolean
+}
+
+/// A Person!
+open class Person extends Being {
+  isAlive = true
+
+  bike: Bike
+
+  /// The person's first name
+  firstName: UInt16?
+
+  /// The person's last name
+  lastName: Mapping<String, UInt32?>
+
+  things: Set<Int>
+}
+
+class ThisPerson extends Person {
+  myself: ThisPerson
+  someoneElse: Person
+}
+
+typealias BugKind = "butterfly"|"beetle\""|"beetle one"
+
+// `nothing` is allowed as a string literal
+typealias BugKindTwo = nothing|"butterfly"|"beetle\""|"beetle one"
+
+// should turn into just a string type because of a conflict; "bettle one" and "bettle_one" would
+// turn into the same Swift identifier.
+typealias BugKindThree = "butterfly"|"beetle\""|"beetle one"|"beetle_one"
+
+// should also turn into just a string type because there no way to generate valid swift symols; "*" and "!!" would
+// turn into invalid Swift symbols.
+typealias BugKindFour = "*"|"!!"
+
+class Bug {
+  /// The owner of this bug.
+  owner: Person?
+
+  /// The age of this bug
+  age: Int?
+
+  /// How long the bug holds its breath for
+  holdsBreathFor: Duration
+
+  size: DataSize
+
+  kind: BugKind
+
+  kind2: BugKindTwo
+
+  kind3: BugKindThree
+
+  kind4: BugKindFour
+
+  bagOfStuff: Dynamic
+
+  bugClass: Class
+
+  bugTypeAlias: TypeAlias
+}
+
+abstract class A {
+  a: "a"
+}
+
+open class B extends A {
+  b: "b"
+}
+
+open class C extends B {
+  c: "c"
 }
 
-open class Animal {
-  name: String
+class D extends C {
+  d: "d"
 }