Add setting for Kotlin package to codegen (#194)

pkl-codegen-kotlin/src/main/kotlin/org/pkl/codegen/kotlin/CliKotlinCodeGeneratorOptions.kt

@@ -29,6 +29,9 @@ data class CliKotlinCodeGeneratorOptions(
   /** The characters to use for indenting generated source code. */
   val indent: String = "  ",
 
+  /** Kotlin package to use for generated code; if none is provided, the root package is used. */
+  val kotlinPackage: String = "",
+
   /** Whether to generate Kdoc based on doc comments for Pkl modules, classes, and properties. */
   val generateKdoc: Boolean = false,
 
@@ -39,5 +42,11 @@ data class CliKotlinCodeGeneratorOptions(
   val implementSerializable: Boolean = false
 ) {
   fun toKotlinCodegenOptions(): KotlinCodegenOptions =
-    KotlinCodegenOptions(indent, generateKdoc, generateSpringBootConfig, implementSerializable)
+    KotlinCodegenOptions(
+      indent = indent,
+      generateKdoc = generateKdoc,
+      generateSpringBootConfig = generateSpringBootConfig,
+      implementSerializable = implementSerializable,
+      kotlinPackage = kotlinPackage,
+    )
 }

pkl-codegen-kotlin/src/main/kotlin/org/pkl/codegen/kotlin/KotlinCodeGenerator.kt

@@ -27,6 +27,9 @@ data class KotlinCodegenOptions(
   /** The characters to use for indenting generated Kotlin code. */
   val indent: String = "  ",
 
+  /** Kotlin package to use for generated code; if none is provided, the root package is used. */
+  val kotlinPackage: String = "",
+
   /** Whether to generate KDoc based on doc comments for Pkl modules, classes, and properties. */
   val generateKdoc: Boolean = false,
 
@@ -111,6 +114,9 @@ class KotlinCodeGenerator(
       append("lin/${relativeOutputPathFor(moduleSchema.moduleName)}")
     }
 
+  val kotlinPackage: String?
+    get() = options.kotlinPackage.ifEmpty { null }
+
   val kotlinFile: String
     get() {
       if (moduleSchema.moduleUri.scheme == "pkl") {
@@ -123,6 +129,7 @@ class KotlinCodeGenerator(
 
       val hasProperties = pModuleClass.properties.any { !it.value.isHidden }
       val isGenerateClass = hasProperties || pModuleClass.isOpen || pModuleClass.isAbstract
+      val packagePrefix = kotlinPackage?.let { "$it." } ?: ""
       val moduleType =
         if (isGenerateClass) {
           generateTypeSpec(pModuleClass, moduleSchema)
@@ -172,7 +179,9 @@ class KotlinCodeGenerator(
       val packageName = if (index == -1) "" else moduleName.substring(0, index)
       val moduleTypeName = moduleName.substring(index + 1).replaceFirstChar { it.titlecaseChar() }
 
-      val fileSpec = FileSpec.builder(packageName, moduleTypeName).indent(options.indent)
+      val packagePath =
+        if (packagePrefix.isNotBlank()) "$packagePrefix.$packageName" else packageName
+      val fileSpec = FileSpec.builder(packagePath, moduleTypeName).indent(options.indent)
 
       for (typeAlias in moduleSchema.typeAliases.values) {
         if (typeAlias.aliasedType is PType.Alias) {
@@ -638,10 +647,14 @@ class KotlinCodeGenerator(
     val index = moduleName.lastIndexOf(".")
     val packageName = if (index == -1) "" else moduleName.substring(0, index)
     val moduleTypeName = moduleName.substring(index + 1).replaceFirstChar { it.titlecaseChar() }
+    val packagePrefix = kotlinPackage?.let { "$it." } ?: ""
+    val renderedPackage =
+      if (packagePrefix.isNotBlank()) "$packagePrefix.$packageName" else packageName
+
     return if (isModuleClass) {
-      ClassName(packageName, moduleTypeName)
+      ClassName(renderedPackage, moduleTypeName)
     } else {
-      ClassName(packageName, moduleTypeName, simpleName)
+      ClassName(renderedPackage, moduleTypeName, simpleName)
     }
   }
 

pkl-codegen-kotlin/src/test/kotlin/org/pkl/codegen/kotlin/KotlinCodeGeneratorTest.kt

@@ -133,7 +133,8 @@ class KotlinCodeGeneratorTest {
       pklCode: String,
       generateKdoc: Boolean = false,
       generateSpringBootConfig: Boolean = false,
-      implementSerializable: Boolean = false
+      implementSerializable: Boolean = false,
+      kotlinPackage: String? = null,
     ): String {
 
       val module = Evaluator.preconfigured().evaluateSchema(ModuleSource.text(pklCode))
@@ -144,7 +145,8 @@ class KotlinCodeGeneratorTest {
           KotlinCodegenOptions(
             generateKdoc = generateKdoc,
             generateSpringBootConfig = generateSpringBootConfig,
-            implementSerializable = implementSerializable
+            implementSerializable = implementSerializable,
+            kotlinPackage = kotlinPackage ?: "",
           )
         )
       return generator.kotlinFile
@@ -553,6 +555,92 @@ class KotlinCodeGeneratorTest {
     assertCompilesSuccessfully(kotlinCode)
   }
 
+  @Test
+  fun `custom kotlin package prefix`() {
+    val kotlinCode =
+      generateKotlinCode(
+        """
+      module my.mod
+
+      class Person {
+        name: String
+        age: Int
+        hobbies: List<String>
+        friends: Map<String, Person>
+        sibling: Person?
+      }
+    """,
+        kotlinPackage = "cool.pkg.path",
+      )
+
+    assertEqualTo(
+      """
+      package cool.pkg.path.my
+
+      import kotlin.Long
+      import kotlin.String
+      import kotlin.collections.List
+      import kotlin.collections.Map
+
+      object Mod {
+        data class Person(
+          val name: String,
+          val age: Long,
+          val hobbies: List<String>,
+          val friends: Map<String, Person>,
+          val sibling: Person?
+        )
+      }
+    """,
+      kotlinCode
+    )
+
+    assertCompilesSuccessfully(kotlinCode)
+  }
+
+  @Test
+  fun `empty kotlin package prefix`() {
+    val kotlinCode =
+      generateKotlinCode(
+        """
+      module my.mod
+
+      class Person {
+        name: String
+        age: Int
+        hobbies: List<String>
+        friends: Map<String, Person>
+        sibling: Person?
+      }
+    """,
+        kotlinPackage = "",
+      )
+
+    assertEqualTo(
+      """
+      package my
+
+      import kotlin.Long
+      import kotlin.String
+      import kotlin.collections.List
+      import kotlin.collections.Map
+
+      object Mod {
+        data class Person(
+          val name: String,
+          val age: Long,
+          val hobbies: List<String>,
+          val friends: Map<String, Person>,
+          val sibling: Person?
+        )
+      }
+    """,
+      kotlinCode
+    )
+
+    assertCompilesSuccessfully(kotlinCode)
+  }
+
   @Test
   fun `recursive types`() {
     val kotlinCode =