Update Kotlin to 2.0 (#900)

- update Kotlin from 1.7.10 to 2.0.21
  - Kotlin 1.6 dependencies in Gradle lock files are expected because kotlinc,
    which is also used by some tests, internally uses some 1.6 dependencies
    for backwards compatibility reasons.
- update kotlinx-html and kotlinx-serialization
- adapt Kotlin code where necessary
- use Kotlin stdlib Path APIs where possible
- fix IntelliJ Kotlin inspection warnings
- reformat code with `./gradlew spotlessApply`
  - ktfmt adds lots of trailing commas
- Add workaround to fix IntelliJ "unresolved reference" errors

pkl-commons-test/src/main/kotlin/org/pkl/commons/test/FakeHttpResponse.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 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.
@@ -25,6 +25,7 @@ import javax.net.ssl.SSLSession
 
 class FakeHttpResponse<T : Any> : HttpResponse<T> {
   companion object {
+    @Suppress("unused")
     fun <T : Any> withBody(block: FakeHttpResponse<T>.() -> Unit): FakeHttpResponse<T> =
       FakeHttpResponse<T>().apply(block)
 

pkl-commons-test/src/main/kotlin/org/pkl/commons/test/InputOutputTestEngine.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 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.
@@ -35,7 +35,7 @@ import org.pkl.commons.toNormalizedPathString
 
 abstract class InputOutputTestEngine :
   HierarchicalTestEngine<InputOutputTestEngine.ExecutionContext>() {
-  protected val rootProjectDir = FileTestUtils.rootProjectDir
+  protected val rootProjectDir: Path = FileTestUtils.rootProjectDir
 
   protected abstract val testClass: KClass<*>
 
@@ -67,7 +67,7 @@ abstract class InputOutputTestEngine :
 
   override fun discover(
     discoveryRequest: EngineDiscoveryRequest,
-    uniqueId: UniqueId
+    uniqueId: UniqueId,
   ): TestDescriptor {
     val packageSelectors = discoveryRequest.getSelectorsByType(PackageSelector::class.java)
     val classSelectors = discoveryRequest.getSelectorsByType(ClassSelector::class.java)
@@ -103,7 +103,7 @@ abstract class InputOutputTestEngine :
 
   private fun doDiscover(
     dirNode: InputDirNode,
-    uniqueIdSelectors: List<UniqueIdSelector>
+    uniqueIdSelectors: List<UniqueIdSelector>,
   ): TestDescriptor {
     dirNode.inputDir.useDirectoryEntries { children ->
       for (child in children) {
@@ -128,7 +128,7 @@ abstract class InputOutputTestEngine :
           dirNode.addChild(
             doDiscover(
               InputDirNode(childId, child, DirectorySource.from(child.toFile())),
-              uniqueIdSelectors
+              uniqueIdSelectors,
             )
           )
         }
@@ -137,12 +137,13 @@ abstract class InputOutputTestEngine :
     return dirNode
   }
 
-  override fun createExecutionContext(request: ExecutionRequest) = ExecutionContext()
+  override fun createExecutionContext(request: ExecutionRequest): ExecutionContext =
+    ExecutionContext()
 
   private open inner class InputDirNode(
     uniqueId: UniqueId,
     val inputDir: Path,
-    source: TestSource
+    source: TestSource,
   ) :
     AbstractTestDescriptor(uniqueId, inputDir.fileName.toString(), source), Node<ExecutionContext> {
     override fun getType() = Type.CONTAINER
@@ -152,7 +153,7 @@ abstract class InputOutputTestEngine :
     AbstractTestDescriptor(
       uniqueId,
       inputFile.fileName.toString(),
-      FileSource.from(inputFile.toFile())
+      FileSource.from(inputFile.toFile()),
     ),
     Node<ExecutionContext> {
 
@@ -160,7 +161,7 @@ abstract class InputOutputTestEngine :
 
     override fun execute(
       context: ExecutionContext,
-      dynamicTestExecutor: DynamicTestExecutor
+      dynamicTestExecutor: DynamicTestExecutor,
     ): ExecutionContext {
 
       val (success, actualOutput) = generateOutputFor(inputFile)

pkl-commons-test/src/main/kotlin/org/pkl/commons/test/PackageServer.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 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.
@@ -22,10 +22,7 @@ import java.security.KeyStore
 import java.util.concurrent.Executors
 import javax.net.ssl.KeyManagerFactory
 import javax.net.ssl.SSLContext
-import kotlin.io.path.inputStream
-import kotlin.io.path.isRegularFile
-import org.pkl.commons.createParentDirectories
-import org.pkl.commons.deleteRecursively
+import kotlin.io.path.*
 
 /**
  * A test HTTP server that serves the Pkl packages defined under
@@ -44,6 +41,7 @@ import org.pkl.commons.deleteRecursively
  * 4. Use port `0` in your test. `HttpClient` will replace this port with the server port.
  * 4. [Close][close] the server, for example in [AfterAll][org.junit.jupiter.api.AfterAll].
  */
+@OptIn(ExperimentalPathApi::class)
 class PackageServer : AutoCloseable {
   companion object {
     const val BIRDS_SHA = "6f18af649b47986530cd6dc39abe17888db2701bc5381c385fb86a32fda2685e"

pkl-commons-test/src/main/kotlin/org/pkl/commons/test/ReflectionUtils.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright © 2024-2025 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.
+ */
+package org.pkl.commons.test
+
+import kotlin.reflect.KClass
+
+object ReflectionUtils {
+  // https://youtrack.jetbrains.com/issue/KT-14743/Reflection-Access-enum-values-and-valueOf-via-KClass#focus=Comments-27-1745309.0-0
+  @Suppress("UNCHECKED_CAST")
+  fun KClass<*>.enumValues(): Array<Enum<*>> = java.enumConstants as Array<Enum<*>>
+}