Support generated adapters for Kotlin superclasses

kotlin-codegen/compiler/src/main/java/com/squareup/moshi/JsonClassCodeGenProcessor.kt

@@ -93,7 +93,7 @@ class JsonClassCodeGenProcessor : KotlinAbstractProcessor(), KotlinMetadataUtils
   }
 
   private fun adapterGenerator(element: Element): AdapterGenerator? {
-    val type = TargetType.get(messager, elementUtils, element) ?: return null
+    val type = TargetType.get(messager, elementUtils, typeUtils, element) ?: return null
 
     val properties = mutableMapOf<String, PropertyGenerator>()
     for (property in type.properties.values) {
@@ -112,8 +112,7 @@ class JsonClassCodeGenProcessor : KotlinAbstractProcessor(), KotlinMetadataUtils
     }
 
     // Sort properties so that those with constructor parameters come first.
-    val sortedProperties = properties.values.toMutableList()
-    sortedProperties.sortBy {
+    val sortedProperties = properties.values.sortedBy {
       if (it.hasConstructorParameter) {
         it.target.parameterIndex
       } else {

kotlin-codegen/compiler/src/main/java/com/squareup/moshi/TargetType.kt

@@ -19,6 +19,7 @@ import com.squareup.kotlinpoet.ClassName
 import com.squareup.kotlinpoet.KModifier
 import com.squareup.kotlinpoet.ParameterizedTypeName
 import com.squareup.kotlinpoet.TypeVariableName
+import com.squareup.kotlinpoet.asClassName
 import com.squareup.kotlinpoet.asTypeName
 import me.eugeniomarletti.kotlin.metadata.KotlinClassMetadata
 import me.eugeniomarletti.kotlin.metadata.KotlinMetadata
@@ -36,10 +37,13 @@ import org.jetbrains.kotlin.serialization.deserialization.NameResolver
 import org.jetbrains.kotlin.util.capitalizeDecapitalize.decapitalizeAsciiOnly
 import javax.annotation.processing.Messager
 import javax.lang.model.element.Element
+import javax.lang.model.element.ElementKind
 import javax.lang.model.element.ExecutableElement
 import javax.lang.model.element.TypeElement
 import javax.lang.model.element.VariableElement
+import javax.lang.model.type.DeclaredType
 import javax.lang.model.util.Elements
+import javax.lang.model.util.Types
 import javax.tools.Diagnostic.Kind.ERROR
 
 /** A user type that should be decoded and encoded by generated code. */
@@ -54,8 +58,10 @@ internal data class TargetType(
   val hasCompanionObject = proto.hasCompanionObjectName()
 
   companion object {
+    private val OBJECT_CLASS = ClassName("java.lang", "Object")
+
     /** Returns a target type for `element`, or null if it cannot be used with code gen. */
-    fun get(messager: Messager, elementUtils: Elements, element: Element): TargetType? {
+    fun get(messager: Messager, elements: Elements, types: Types, element: Element): TargetType? {
       val typeMetadata: KotlinMetadata? = element.kotlinMetadata
       if (element !is TypeElement || typeMetadata !is KotlinClassMetadata) {
         messager.printMessage(
@@ -87,17 +93,34 @@ internal data class TargetType(
         }
       }
 
-      val constructor = TargetConstructor.primary(typeMetadata, elementUtils)
-      val properties = properties(element, constructor)
+      val constructor = TargetConstructor.primary(typeMetadata, elements)
+      val properties = mutableMapOf<String, TargetProperty>()
+      for (supertype in element.supertypes(types)) {
+        if (supertype.asClassName() == OBJECT_CLASS) {
+          continue // Don't load properties for java.lang.Object.
+        }
+        if (supertype.kind != ElementKind.CLASS) {
+          continue // Don't load properties for interface types.
+        }
+        if (supertype.kotlinMetadata == null) {
+          messager.printMessage(ERROR,
+              "@JsonClass can't be applied to $element: supertype $supertype is not a Kotlin type",
+              element)
+        }
+        for ((name, property) in declaredProperties(supertype, constructor)) {
+          properties.putIfAbsent(name, property)
+        }
+      }
       val genericTypeNames = genericTypeNames(proto, typeMetadata.data.nameResolver)
       return TargetType(proto, element, constructor, properties, genericTypeNames)
     }
 
-    private fun properties(
-      model: TypeElement,
+    /** Returns the properties declared by `typeElement`. */
+    private fun declaredProperties(
+      typeElement: TypeElement,
       constructor: TargetConstructor
     ): Map<String, TargetProperty> {
-      val typeMetadata: KotlinClassMetadata = model.kotlinMetadata as KotlinClassMetadata
+      val typeMetadata: KotlinClassMetadata = typeElement.kotlinMetadata as KotlinClassMetadata
       val nameResolver = typeMetadata.data.nameResolver
       val classProto = typeMetadata.data.classProto
 
@@ -105,7 +128,7 @@ internal data class TargetType(
       val fields = mutableMapOf<String, VariableElement>()
       val setters = mutableMapOf<String, ExecutableElement>()
       val getters = mutableMapOf<String, ExecutableElement>()
-      for (element in model.enclosedElements) {
+      for (element in typeElement.enclosedElements) {
         if (element is VariableElement) {
           fields[element.name] = element
         } else if (element is ExecutableElement) {
@@ -157,6 +180,19 @@ internal data class TargetType(
         }
       }
 
+    /** Returns all supertypes of this, recursively. Includes interface and class supertypes. */
+    private fun TypeElement.supertypes(
+      types: Types,
+      result: MutableSet<TypeElement> = mutableSetOf()
+    ): Set<TypeElement> {
+      result.add(this)
+      for (supertype in types.directSupertypes(asType())) {
+        val supertypeElement = (supertype as DeclaredType).asElement() as TypeElement
+        supertypeElement.supertypes(types, result)
+      }
+      return result
+    }
+
     private val Element.name get() = simpleName.toString()
 
     private fun genericTypeNames(proto: Class, nameResolver: NameResolver): List<TypeVariableName> {

kotlin-codegen/compiler/src/test/java/com/squareup/moshi/CompilerTest.kt

@@ -227,4 +227,21 @@ class CompilerTest {
     assertThat(result.systemErr).contains("property b is not visible")
     assertThat(result.systemErr).contains("property c is not visible")
   }
+
+  @Test fun extendPlatformType() {
+    val call = KotlinCompilerCall(temporaryFolder.root)
+    call.inheritClasspath = true
+    call.addService(Processor::class, JsonClassCodeGenProcessor::class)
+    call.addKt("source.kt", """
+        |import com.squareup.moshi.JsonClass
+        |import java.util.Date
+        |
+        |@JsonClass(generateAdapter = true)
+        |class ExtendsPlatformClass(var a: Int) : Date()
+        |""".trimMargin())
+
+    val result = call.execute()
+    assertThat(result.exitCode).isEqualTo(ExitCode.COMPILATION_ERROR)
+    assertThat(result.systemErr).contains("supertype java.util.Date is not a Kotlin type")
+  }
 }

kotlin-codegen/integration-test/src/test/kotlin/com/squareup/moshi/GeneratedAdaptersTest.kt

@@ -20,7 +20,6 @@ import org.intellij.lang.annotations.Language
 import org.junit.Assert.fail
 import org.junit.Test
 import java.util.Locale
-import java.util.SimpleTimeZone
 
 class GeneratedAdaptersTest {
 
@@ -628,21 +627,6 @@ class GeneratedAdaptersTest {
     var v26: Int, var v27: Int, var v28: Int, var v29: Int, var v30: Int,
     var v31: Int, var v32: Int, var v33: Int)
 
-  @Test fun extendsPlatformClassWithPrivateField() {
-    val moshi = Moshi.Builder().build()
-    val jsonAdapter = moshi.adapter(ExtendsPlatformClassWithPrivateField::class.java)
-
-    val encoded = ExtendsPlatformClassWithPrivateField(3)
-    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"a":3}""")
-
-    val decoded = jsonAdapter.fromJson("""{"a":4,"id":"B"}""")!!
-    assertThat(decoded.a).isEqualTo(4)
-    assertThat(decoded.id).isEqualTo("C")
-  }
-
-  @JsonClass(generateAdapter = true)
-  internal class ExtendsPlatformClassWithPrivateField(var a: Int) : SimpleTimeZone(0, "C")
-
   @Test fun unsettablePropertyIgnored() {
     val moshi = Moshi.Builder().build()
     val jsonAdapter = moshi.adapter(UnsettableProperty::class.java)
@@ -710,6 +694,46 @@ class GeneratedAdaptersTest {
       }
   }
 
+  @Test fun supertypeConstructorParameters() {
+    val moshi = Moshi.Builder().build()
+    val jsonAdapter = moshi.adapter(SubtypeConstructorParameters::class.java)
+
+    val encoded = SubtypeConstructorParameters(3, 5)
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"a":3,"b":5}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
+    assertThat(decoded.a).isEqualTo(4)
+    assertThat(decoded.b).isEqualTo(6)
+  }
+
+  open class SupertypeConstructorParameters(var a: Int)
+
+  @JsonClass(generateAdapter = true)
+  class SubtypeConstructorParameters(a: Int, var b: Int) : SupertypeConstructorParameters(a)
+
+  @Test fun supertypeProperties() {
+    val moshi = Moshi.Builder().build()
+    val jsonAdapter = moshi.adapter(SubtypeProperties::class.java)
+
+    val encoded = SubtypeProperties()
+    encoded.a = 3
+    encoded.b = 5
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"b":5,"a":3}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
+    assertThat(decoded.a).isEqualTo(4)
+    assertThat(decoded.b).isEqualTo(6)
+  }
+
+  open class SupertypeProperties {
+    var a: Int = -1
+  }
+
+  @JsonClass(generateAdapter = true)
+  class SubtypeProperties : SupertypeProperties() {
+    var b: Int = -1
+  }
+
   @Retention(AnnotationRetention.RUNTIME)
   @JsonQualifier
   annotation class Uppercase

moshi/src/main/java/com/squareup/moshi/JsonClass.java

@@ -22,11 +22,20 @@ import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
 /**
  * Customizes how a type is encoded as JSON.
- *
- * <p>This annotation is currently only permitted on declarations of classes in Kotlin.
  */
 @Retention(RUNTIME)
 @Documented
 public @interface JsonClass {
+  /**
+   * True to trigger the annotation processor to generate an adapter for this type.
+   *
+   * There are currently some restrictions on which types that can be used with generated adapters:
+   *
+   *  * The class must be implemented in Kotlin.
+   *  * The class may not be an abstract class, an inner class, or a local class.
+   *  * All superclasses must be implemented in Kotlin.
+   *  * All properties must be public, protected, or internal.
+   *  * All properties must be either non-transient or have a default value.
+   */
   boolean generateAdapter();
 }