Add @Json.ignore (#1417)

* Default Json.name to an unset value

* Promote shared transient tests to DualKotlinTest

* Add new ignore property to Json

* Support it in ClassJsonAdapter

* Mention no enum/record support

* Support in KotlinJsonAdapter

* Rework code gen API to know of "ignored"

* Support in apt code gen

* Support in KSP

* Update old non-working transient example test

* Synthetic holders

* Use field on both

adapters/src/main/java/com/squareup/moshi/adapters/EnumJsonAdapter.java

@@ -68,7 +68,10 @@ public final class EnumJsonAdapter<T extends Enum<T>> extends JsonAdapter<T> {
       for (int i = 0; i < constants.length; i++) {
         String constantName = constants[i].name();
         Json annotation = enumType.getField(constantName).getAnnotation(Json.class);
-        String name = annotation != null ? annotation.name() : constantName;
+        String name =
+            annotation != null && !Json.UNSET_NAME.equals(annotation.name())
+                ? annotation.name()
+                : constantName;
         nameStrings[i] = name;
       }
       options = JsonReader.Options.of(nameStrings);

examples/src/main/java/com/squareup/moshi/recipes/FallbackEnum.java

@@ -79,7 +79,10 @@ final class FallbackEnum {
         for (int i = 0; i < constants.length; i++) {
           T constant = constants[i];
           Json annotation = enumType.getField(constant.name()).getAnnotation(Json.class);
-          String name = annotation != null ? annotation.name() : constant.name();
+          String name =
+              annotation != null && !Json.UNSET_NAME.equals(annotation.name())
+                  ? annotation.name()
+                  : constant.name();
           nameStrings[i] = name;
         }
         options = JsonReader.Options.of(nameStrings);

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/api/TargetParameter.kt

@@ -26,5 +26,6 @@ public data class TargetParameter(
   val type: TypeName,
   val hasDefault: Boolean,
   val jsonName: String? = null,
+  val jsonIgnore: Boolean = false,
   val qualifiers: Set<AnnotationSpec>? = null
 )

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/api/TargetProperty.kt

@@ -25,7 +25,8 @@ public data class TargetProperty(
   val propertySpec: PropertySpec,
   val parameter: TargetParameter?,
   val visibility: KModifier,
-  val jsonName: String?
+  val jsonName: String?,
+  val jsonIgnore: Boolean
 ) {
   val name: String get() = propertySpec.name
   val type: TypeName get() = propertySpec.type

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/apt/metadata.kt

@@ -64,6 +64,7 @@ import javax.tools.Diagnostic.Kind.WARNING
 
 private val JSON_QUALIFIER = JsonQualifier::class.java
 private val JSON = Json::class.asClassName()
+private val TRANSIENT = Transient::class.asClassName()
 private val OBJECT_CLASS = ClassName("java.lang", "Object")
 private val VISIBILITY_MODIFIERS = setOf(
   KModifier.INTERNAL,
@@ -95,7 +96,8 @@ internal fun primaryConstructor(
       type = parameter.type,
       hasDefault = parameter.defaultValue != null,
       qualifiers = parameter.annotations.qualifiers(messager, elements),
-      jsonName = parameter.annotations.jsonName()
+      jsonName = parameter.annotations.jsonName(),
+      jsonIgnore = parameter.annotations.jsonIgnore(),
     )
   }
 
@@ -386,7 +388,6 @@ private fun declaredProperties(
   currentClass: ClassName,
   resolvedTypes: List<ResolvedTypeMapping>
 ): Map<String, TargetProperty> {
-
   val result = mutableMapOf<String, TargetProperty>()
   for (initialProperty in kotlinApi.propertySpecs) {
     val resolvedType = resolveTypeArgs(
@@ -398,19 +399,22 @@ private fun declaredProperties(
     val property = initialProperty.toBuilder(type = resolvedType).build()
     val name = property.name
     val parameter = constructor.parameters[name]
+    val isIgnored = property.annotations.any { it.typeName == TRANSIENT } ||
+      parameter?.jsonIgnore == true ||
+      property.annotations.jsonIgnore()
     result[name] = TargetProperty(
       propertySpec = property,
       parameter = parameter,
       visibility = property.modifiers.visibility(),
       jsonName = parameter?.jsonName ?: property.annotations.jsonName()
-        ?: name.escapeDollarSigns()
+        ?: name.escapeDollarSigns(),
+      jsonIgnore = isIgnored
     )
   }
 
   return result
 }
 
-private val TargetProperty.isTransient get() = propertySpec.annotations.any { it.typeName == Transient::class.asClassName() }
 private val TargetProperty.isSettable get() = propertySpec.mutable || parameter != null
 private val TargetProperty.isVisible: Boolean
   get() {
@@ -429,11 +433,11 @@ internal fun TargetProperty.generator(
   elements: Elements,
   instantiateAnnotations: Boolean
 ): PropertyGenerator? {
-  if (isTransient) {
+  if (jsonIgnore) {
     if (!hasDefault) {
       messager.printMessage(
         ERROR,
-        "No default value for transient property $name",
+        "No default value for transient/ignored property $name",
         sourceElement
       )
       return null
@@ -510,16 +514,36 @@ private fun List<AnnotationSpec>?.qualifiers(
 
 private fun List<AnnotationSpec>?.jsonName(): String? {
   if (this == null) return null
-  return find { it.typeName == JSON }?.let { annotation ->
+  return filter { it.typeName == JSON }.firstNotNullOfOrNull { annotation ->
-    val mirror = requireNotNull(annotation.tag<AnnotationMirror>()) {
+    annotation.jsonName()
-      "Could not get the annotation mirror from the annotation spec"
-    }
-    mirror.elementValues.entries.single {
-      it.key.simpleName.contentEquals("name")
-    }.value.value as String
   }
 }
 
+private fun List<AnnotationSpec>?.jsonIgnore(): Boolean {
+  if (this == null) return false
+  return filter { it.typeName == JSON }.firstNotNullOfOrNull { annotation ->
+    annotation.jsonIgnore()
+  } ?: false
+}
+
+private fun AnnotationSpec.jsonName(): String? {
+  return elementValue<String>("name").takeUnless { it == Json.UNSET_NAME }
+}
+
+private fun AnnotationSpec.jsonIgnore(): Boolean {
+  return elementValue<Boolean>("ignore") ?: false
+}
+
+private fun <T> AnnotationSpec.elementValue(name: String): T? {
+  val mirror = requireNotNull(tag<AnnotationMirror>()) {
+    "Could not get the annotation mirror from the annotation spec"
+  }
+  @Suppress("UNCHECKED_CAST")
+  return mirror.elementValues.entries.firstOrNull {
+    it.key.simpleName.contentEquals(name)
+  }?.value?.value as? T
+}
+
 private fun String.escapeDollarSigns(): String {
   return replace("\$", "\${\'\$\'}")
 }

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/ksp/MoshiApiUtil.kt

@@ -21,14 +21,12 @@ import com.google.devtools.ksp.symbol.KSClassDeclaration
 import com.google.devtools.ksp.symbol.KSDeclaration
 import com.squareup.kotlinpoet.AnnotationSpec
 import com.squareup.kotlinpoet.KModifier
-import com.squareup.kotlinpoet.asClassName
 import com.squareup.moshi.JsonQualifier
 import com.squareup.moshi.kotlin.codegen.api.DelegateKey
 import com.squareup.moshi.kotlin.codegen.api.PropertyGenerator
 import com.squareup.moshi.kotlin.codegen.api.TargetProperty
 import com.squareup.moshi.kotlin.codegen.api.rawType
 
-private val TargetProperty.isTransient get() = propertySpec.annotations.any { it.typeName == Transient::class.asClassName() }
 private val TargetProperty.isSettable get() = propertySpec.mutable || parameter != null
 private val TargetProperty.isVisible: Boolean
   get() {
@@ -47,10 +45,10 @@ internal fun TargetProperty.generator(
   originalType: KSDeclaration,
   instantiateAnnotations: Boolean
 ): PropertyGenerator? {
-  if (isTransient) {
+  if (jsonIgnore) {
     if (!hasDefault) {
       logger.error(
-        "No default value for transient property $name",
+        "No default value for transient/ignored property $name",
         originalType
       )
       return null

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/ksp/TargetTypes.kt

@@ -213,7 +213,11 @@ private fun KSAnnotated?.qualifiers(resolver: Resolver): Set<AnnotationSpec> {
 }
 
 private fun KSAnnotated?.jsonName(): String? {
-  return this?.findAnnotationWithType<Json>()?.name
+  return this?.findAnnotationWithType<Json>()?.name?.takeUnless { it == Json.UNSET_NAME }
+}
+
+private fun KSAnnotated?.jsonIgnore(): Boolean {
+  return this?.findAnnotationWithType<Json>()?.ignore ?: false
 }
 
 private fun declaredProperties(
@@ -223,7 +227,6 @@ private fun declaredProperties(
   resolver: Resolver,
   typeParameterResolver: TypeParameterResolver,
 ): Map<String, TargetProperty> {
-
   val result = mutableMapOf<String, TargetProperty>()
   for (property in classDecl.getDeclaredProperties()) {
     val initialType = property.type.resolve()
@@ -235,12 +238,14 @@ private fun declaredProperties(
     val propertySpec = property.toPropertySpec(resolver, resolvedType, typeParameterResolver)
     val name = propertySpec.name
     val parameter = constructor.parameters[name]
+    val isTransient = property.isAnnotationPresent(Transient::class)
     result[name] = TargetProperty(
       propertySpec = propertySpec,
       parameter = parameter,
       visibility = property.getVisibility().toKModifier() ?: KModifier.PUBLIC,
       jsonName = parameter?.jsonName ?: property.jsonName()
-        ?: name.escapeDollarSigns()
+        ?: name.escapeDollarSigns(),
+      jsonIgnore = isTransient || parameter?.jsonIgnore == true || property.jsonIgnore()
     )
   }
 

kotlin/codegen/src/test/java/com/squareup/moshi/kotlin/codegen/apt/JsonClassCodegenProcessorTest.kt

@@ -334,7 +334,27 @@ class JsonClassCodegenProcessorTest(
     )
     assertThat(result.exitCode).isEqualTo(KotlinCompilation.ExitCode.COMPILATION_ERROR)
     assertThat(result.messages).contains(
-      "error: No default value for transient property a"
+      "error: No default value for transient/ignored property a"
+    )
+  }
+
+  @Test
+  fun requiredIgnoredConstructorParameterFails() {
+    val result = compile(
+      kotlin(
+        "source.kt",
+        """
+          import com.squareup.moshi.Json
+          import com.squareup.moshi.JsonClass
+
+          @JsonClass(generateAdapter = true)
+          class RequiredIgnoredConstructorParameter(@Json(ignore = true) var a: Int)
+          """
+      )
+    )
+    assertThat(result.exitCode).isEqualTo(KotlinCompilation.ExitCode.COMPILATION_ERROR)
+    assertThat(result.messages).contains(
+      "error: No default value for transient/ignored property a"
     )
   }
 

kotlin/codegen/src/test/java/com/squareup/moshi/kotlin/codegen/ksp/JsonClassSymbolProcessorTest.kt

@@ -357,7 +357,28 @@ class JsonClassSymbolProcessorTest(
     )
     assertThat(result.exitCode).isEqualTo(KotlinCompilation.ExitCode.COMPILATION_ERROR)
     assertThat(result.messages).contains(
-      "No default value for transient property a"
+      "No default value for transient/ignored property a"
+    )
+  }
+
+  @Test
+  fun requiredIgnoredConstructorParameterFails() {
+    val result = compile(
+      kotlin(
+        "source.kt",
+        """
+          package test
+          import com.squareup.moshi.Json
+          import com.squareup.moshi.JsonClass
+
+          @JsonClass(generateAdapter = true)
+          class RequiredTransientConstructorParameter(@Json(ignore = true) var a: Int)
+          """
+      )
+    )
+    assertThat(result.exitCode).isEqualTo(KotlinCompilation.ExitCode.COMPILATION_ERROR)
+    assertThat(result.messages).contains(
+      "No default value for transient/ignored property a"
     )
   }
 

kotlin/reflect/src/main/java/com/squareup/moshi/kotlin/reflect/KotlinJsonAdapter.kt

@@ -57,7 +57,7 @@ private val ABSENT_VALUE = Any()
 internal class KotlinJsonAdapter<T>(
   val constructor: KFunction<T>,
   val allBindings: List<Binding<T, Any?>?>,
-  val nonTransientBindings: List<Binding<T, Any?>>,
+  val nonIgnoredBindings: List<Binding<T, Any?>>,
   val options: JsonReader.Options
 ) : JsonAdapter<T>() {
 
@@ -74,7 +74,7 @@ internal class KotlinJsonAdapter<T>(
         reader.skipValue()
         continue
       }
-      val binding = nonTransientBindings[index]
+      val binding = nonIgnoredBindings[index]
 
       val propertyIndex = binding.propertyIndex
       if (values[propertyIndex] !== ABSENT_VALUE) {
@@ -235,11 +235,27 @@ public class KotlinJsonAdapterFactory : JsonAdapter.Factory {
     for (property in rawTypeKotlin.memberProperties) {
       val parameter = parametersByName[property.name]
 
+      property.isAccessible = true
+      var jsonAnnotation = property.findAnnotation<Json>()
+      val allAnnotations = property.annotations.toMutableList()
+
+      if (parameter != null) {
+        allAnnotations += parameter.annotations
+        if (jsonAnnotation == null) {
+          jsonAnnotation = parameter.findAnnotation()
+        }
+      }
+
       if (Modifier.isTransient(property.javaField?.modifiers ?: 0)) {
         require(parameter == null || parameter.isOptional) {
           "No default value for transient constructor $parameter"
         }
         continue
+      } else if (jsonAnnotation?.ignore == true) {
+        require(parameter == null || parameter.isOptional) {
+          "No default value for ignored constructor $parameter"
+        }
+        continue
       }
 
       require(parameter == null || parameter.type == property.returnType) {
@@ -248,18 +264,7 @@ public class KotlinJsonAdapterFactory : JsonAdapter.Factory {
 
       if (property !is KMutableProperty1 && parameter == null) continue
 
-      property.isAccessible = true
+      val name = jsonAnnotation?.name?.takeUnless { it == Json.UNSET_NAME } ?: property.name
-      val allAnnotations = property.annotations.toMutableList()
-      var jsonAnnotation = property.findAnnotation<Json>()
-
-      if (parameter != null) {
-        allAnnotations += parameter.annotations
-        if (jsonAnnotation == null) {
-          jsonAnnotation = parameter.findAnnotation()
-        }
-      }
-
-      val name = jsonAnnotation?.name ?: property.name
       val propertyType = when (val propertyTypeClassifier = property.returnType.classifier) {
         is KClass<*> -> {
           if (propertyTypeClassifier.isValue) {
@@ -294,7 +299,7 @@ public class KotlinJsonAdapterFactory : JsonAdapter.Factory {
       @Suppress("UNCHECKED_CAST")
       bindingsByName[property.name] = KotlinJsonAdapter.Binding(
         name,
-        jsonAnnotation?.name ?: name,
+        jsonAnnotation?.name?.takeUnless { it == Json.UNSET_NAME } ?: name,
         adapter,
         property as KProperty1<Any, Any?>,
         parameter,
@@ -317,8 +322,8 @@ public class KotlinJsonAdapterFactory : JsonAdapter.Factory {
       bindings += bindingByName.value.copy(propertyIndex = index++)
     }
 
-    val nonTransientBindings = bindings.filterNotNull()
+    val nonIgnoredBindings = bindings.filterNotNull()
-    val options = JsonReader.Options.of(*nonTransientBindings.map { it.name }.toTypedArray())
+    val options = JsonReader.Options.of(*nonIgnoredBindings.map { it.name }.toTypedArray())
-    return KotlinJsonAdapter(constructor, bindings, nonTransientBindings, options).nullSafe()
+    return KotlinJsonAdapter(constructor, bindings, nonIgnoredBindings, options).nullSafe()
   }
 }

kotlin/tests/extra-moshi-test-module/build.gradle.kts

@@ -17,3 +17,7 @@
 plugins {
   kotlin("jvm")
 }
+
+dependencies {
+  implementation(project(":moshi"))
+}

kotlin/tests/extra-moshi-test-module/src/main/kotlin/com/squareup/moshi/kotlin/codegen/test/extra/AbstractClassInModuleA.kt

@@ -15,10 +15,14 @@
  */
 package com.squareup.moshi.kotlin.codegen.test.extra
 
+import com.squareup.moshi.Json
+
 public abstract class AbstractClassInModuleA {
-  // Transients to ensure processor sees them across module boundaries since @Transient is
+  // Ignored to ensure processor sees them across module boundaries.
-  // SOURCE-only
+  // @Transient doesn't work for this case because it's source-only and jvm modifiers aren't currently visible in KSP.
-  // TODO uncomment these when https://github.com/google/ksp/issues/710 is fixed
+
-//  @Transient private lateinit var lateinitTransient: String
+  // Note that we target the field because otherwise it is stored on the synthetic holder method for
-//  @Transient private var regularTransient: String = "regularTransient"
+  // annotations, which isn't visible from kapt
+  @field:Json(ignore = true) private lateinit var lateinitIgnored: String
+  @field:Json(ignore = true) private var regularIgnored: String = "regularIgnored"
 }

kotlin/tests/src/test/kotlin/com/squareup/moshi/kotlin/DualKotlinTest.kt

@@ -625,6 +625,124 @@ class DualKotlinTest {
   data class IntersectionTypes<E>(
     val value: E
   ) where E : Enum<E>, E : IntersectionTypeInterface<E>
+
+  @Test fun transientConstructorParameter() {
+    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter<TransientConstructorParameter>()
+
+    val encoded = TransientConstructorParameter(3, 5)
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"b":5}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
+    assertThat(decoded.a).isEqualTo(-1)
+    assertThat(decoded.b).isEqualTo(6)
+  }
+
+  class TransientConstructorParameter(@Transient var a: Int = -1, var b: Int = -1)
+
+  @Test fun multipleTransientConstructorParameters() {
+    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter(MultipleTransientConstructorParameters::class.java)
+
+    val encoded = MultipleTransientConstructorParameters(3, 5, 7)
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"b":5}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
+    assertThat(decoded.a).isEqualTo(-1)
+    assertThat(decoded.b).isEqualTo(6)
+    assertThat(decoded.c).isEqualTo(-1)
+  }
+
+  class MultipleTransientConstructorParameters(@Transient var a: Int = -1, var b: Int = -1, @Transient var c: Int = -1)
+
+  @Test fun transientProperty() {
+    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter<TransientProperty>()
+
+    val encoded = TransientProperty()
+    encoded.a = 3
+    encoded.setB(4)
+    encoded.c = 5
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"c":5}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":5,"c":6}""")!!
+    assertThat(decoded.a).isEqualTo(-1)
+    assertThat(decoded.getB()).isEqualTo(-1)
+    assertThat(decoded.c).isEqualTo(6)
+  }
+
+  class TransientProperty {
+    @Transient var a: Int = -1
+    @Transient private var b: Int = -1
+    var c: Int = -1
+
+    fun getB() = b
+
+    fun setB(b: Int) {
+      this.b = b
+    }
+  }
+
+  @Test fun ignoredConstructorParameter() {
+    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter<IgnoredConstructorParameter>()
+
+    val encoded = IgnoredConstructorParameter(3, 5)
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"b":5}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
+    assertThat(decoded.a).isEqualTo(-1)
+    assertThat(decoded.b).isEqualTo(6)
+  }
+
+  class IgnoredConstructorParameter(@Json(ignore = true) var a: Int = -1, var b: Int = -1)
+
+  @Test fun multipleIgnoredConstructorParameters() {
+    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter(MultipleIgnoredConstructorParameters::class.java)
+
+    val encoded = MultipleIgnoredConstructorParameters(3, 5, 7)
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"b":5}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
+    assertThat(decoded.a).isEqualTo(-1)
+    assertThat(decoded.b).isEqualTo(6)
+    assertThat(decoded.c).isEqualTo(-1)
+  }
+
+  class MultipleIgnoredConstructorParameters(
+    @Json(ignore = true) var a: Int = -1,
+    var b: Int = -1,
+    @Json(ignore = true) var c: Int = -1
+  )
+
+  @Test fun ignoredProperty() {
+    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter<IgnoredProperty>()
+
+    val encoded = IgnoredProperty()
+    encoded.a = 3
+    encoded.setB(4)
+    encoded.c = 5
+    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"c":5}""")
+
+    val decoded = jsonAdapter.fromJson("""{"a":4,"b":5,"c":6}""")!!
+    assertThat(decoded.a).isEqualTo(-1)
+    assertThat(decoded.getB()).isEqualTo(-1)
+    assertThat(decoded.c).isEqualTo(6)
+  }
+
+  class IgnoredProperty {
+    @Json(ignore = true) var a: Int = -1
+    @Json(ignore = true) private var b: Int = -1
+    var c: Int = -1
+
+    fun getB() = b
+
+    fun setB(b: Int) {
+      this.b = b
+    }
+  }
 }
 
 typealias TypeAlias = Int

kotlin/tests/src/test/kotlin/com/squareup/moshi/kotlin/reflect/KotlinJsonAdapterTest.kt

@@ -278,35 +278,6 @@ class KotlinJsonAdapterTest {
     var b: Int = -1
   }
 
-  @Test fun transientConstructorParameter() {
-    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter<TransientConstructorParameter>()
-
-    val encoded = TransientConstructorParameter(3, 5)
-    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"b":5}""")
-
-    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
-    assertThat(decoded.a).isEqualTo(-1)
-    assertThat(decoded.b).isEqualTo(6)
-  }
-
-  class TransientConstructorParameter(@Transient var a: Int = -1, var b: Int = -1)
-
-  @Test fun multipleTransientConstructorParameters() {
-    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter(MultipleTransientConstructorParameters::class.java)
-
-    val encoded = MultipleTransientConstructorParameters(3, 5, 7)
-    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"b":5}""")
-
-    val decoded = jsonAdapter.fromJson("""{"a":4,"b":6}""")!!
-    assertThat(decoded.a).isEqualTo(-1)
-    assertThat(decoded.b).isEqualTo(6)
-    assertThat(decoded.c).isEqualTo(-1)
-  }
-
-  class MultipleTransientConstructorParameters(@Transient var a: Int = -1, var b: Int = -1, @Transient var c: Int = -1)
-
   @Test fun requiredTransientConstructorParameterFails() {
     val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
     try {
@@ -323,34 +294,22 @@ class KotlinJsonAdapterTest {
 
   class RequiredTransientConstructorParameter(@Transient var a: Int)
 
-  @Test fun transientProperty() {
+  @Test fun requiredIgnoredConstructorParameterFails() {
     val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter<TransientProperty>()
+    try {
-
+      moshi.adapter<RequiredIgnoredConstructorParameter>()
-    val encoded = TransientProperty()
+      fail()
-    encoded.a = 3
+    } catch (expected: IllegalArgumentException) {
-    encoded.setB(4)
+      assertThat(expected).hasMessageThat().isEqualTo(
-    encoded.c = 5
+        "No default value for ignored constructor parameter #0 " +
-    assertThat(jsonAdapter.toJson(encoded)).isEqualTo("""{"c":5}""")
+          "a of fun <init>(kotlin.Int): " +
-
+          "com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterTest.RequiredIgnoredConstructorParameter"
-    val decoded = jsonAdapter.fromJson("""{"a":4,"b":5,"c":6}""")!!
+      )
-    assertThat(decoded.a).isEqualTo(-1)
-    assertThat(decoded.getB()).isEqualTo(-1)
-    assertThat(decoded.c).isEqualTo(6)
-  }
-
-  class TransientProperty {
-    @Transient var a: Int = -1
-    @Transient private var b: Int = -1
-    var c: Int = -1
-
-    fun getB() = b
-
-    fun setB(b: Int) {
-      this.b = b
     }
   }
 
+  class RequiredIgnoredConstructorParameter(@Json(ignore = true) var a: Int)
+
   @Test fun constructorParametersAndPropertiesWithSameNamesMustHaveSameTypes() {
     val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
     try {

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

@@ -134,6 +134,8 @@ final class ClassJsonAdapter<T> extends JsonAdapter<T> {
           boolean platformType = Util.isPlatformType(rawType);
           for (Field field : rawType.getDeclaredFields()) {
             if (!includeField(platformType, field.getModifiers())) continue;
+            Json jsonAnnotation = field.getAnnotation(Json.class);
+            if (jsonAnnotation != null && jsonAnnotation.ignore()) continue;
 
             // Look up a type adapter for this type.
             Type fieldType = resolve(type, rawType, field.getGenericType());
@@ -145,8 +147,10 @@ final class ClassJsonAdapter<T> extends JsonAdapter<T> {
             field.setAccessible(true);
 
             // Store it using the field's name. If there was already a field with this name, fail!
-            Json jsonAnnotation = field.getAnnotation(Json.class);
+            String name =
-            String name = jsonAnnotation != null ? jsonAnnotation.name() : fieldName;
+                jsonAnnotation != null && !Json.UNSET_NAME.equals(jsonAnnotation.name())
+                    ? jsonAnnotation.name()
+                    : fieldName;
             FieldBinding<Object> fieldBinding = new FieldBinding<>(name, field, adapter);
             FieldBinding<?> replaced = fieldBindings.put(name, fieldBinding);
             if (replaced != null) {

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

@@ -29,8 +29,9 @@ import java.lang.annotation.Target;
  *
  * <ul>
  *   <li><strong>Java class fields</strong>
- *   <li><strong>Kotlin properties</strong> for use with {@code moshi-kotlin}. This includes both
+ *   <li><strong>Kotlin properties</strong> for use with {@code moshi-kotlin} or {@code
- *       properties declared in the constructor and properties declared as members.
+ *       moshi-kotlin-codegen}. This includes both properties declared in the constructor and
+ *       properties declared as members.
  * </ul>
  *
  * <p>Users of the <a href="https://github.com/rharter/auto-value-moshi">AutoValue: Moshi
@@ -39,5 +40,17 @@ import java.lang.annotation.Target;
 @Retention(RUNTIME)
 @Documented
 public @interface Json {
-  String name();
+  /** The default value of {@link #name()}. Should only be used to check if it's been set. */
+  String UNSET_NAME = "\u0000";
+
+  /** The name of the field when encoded as JSON. */
+  String name() default UNSET_NAME;
+
+  /**
+   * If true, this field/property will be ignored. This is semantically similar to use of {@code
+   * transient} on the JVM.
+   *
+   * <p><strong>Note:</strong> this has no effect in enums or record classes.
+   */
+  boolean ignore() default false;
 }

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

@@ -275,7 +275,10 @@ final class StandardJsonAdapters {
         for (int i = 0; i < constants.length; i++) {
           T constant = constants[i];
           Json annotation = enumType.getField(constant.name()).getAnnotation(Json.class);
-          String name = annotation != null ? annotation.name() : constant.name();
+          String name =
+              annotation != null && !Json.UNSET_NAME.equals(annotation.name())
+                  ? annotation.name()
+                  : constant.name();
           nameStrings[i] = name;
         }
         options = JsonReader.Options.of(nameStrings);

moshi/src/main/java16/com/squareup/moshi/RecordJsonAdapter.java

@@ -91,7 +91,10 @@ final class RecordJsonAdapter<T> extends JsonAdapter<T> {
           Set<Annotation> qualifiers = null;
           for (var annotation : component.getDeclaredAnnotations()) {
             if (annotation instanceof Json jsonAnnotation) {
-              jsonName = jsonAnnotation.name();
+              var annotationName = jsonAnnotation.name();
+              if (!Json.UNSET_NAME.equals(annotationName)) {
+                jsonName = jsonAnnotation.name();
+              }
             } else {
               if (annotation.annotationType().isAnnotationPresent(JsonQualifier.class)) {
                 if (qualifiers == null) {

moshi/src/test/java/com/squareup/moshi/ClassJsonAdapterTest.java

@@ -153,6 +153,26 @@ public final class ClassJsonAdapterTest {
     assertThat(fromJson.b).isEqualTo(12);
   }
 
+  static class IgnoredFields {
+    @Json(ignore = true)
+    int a;
+
+    int b;
+  }
+
+  @Test
+  public void ignoredFieldsOmitted() throws Exception {
+    IgnoredFields value = new IgnoredFields();
+    value.a = 11;
+    value.b = 12;
+    String toJson = toJson(IgnoredFields.class, value);
+    assertThat(toJson).isEqualTo("{\"b\":12}");
+
+    IgnoredFields fromJson = fromJson(IgnoredFields.class, "{\"a\":13,\"b\":12}");
+    assertThat(fromJson.a).isEqualTo(0); // Not assigned.
+    assertThat(fromJson.b).isEqualTo(12);
+  }
+
   static class BaseA {
     int a;
   }