Report json name if different from property name in kotlin (#917)

* Report json name in code gen if different from property name

Resolves #800

* Unify required property name error message

* Report json name in kotlinjsonadapter, match code gen

* Upper case JSON

Co-Authored-By: Jake Wharton <jakew@google.com>

* Upper case JSON

Co-Authored-By: Jake Wharton <jakew@google.com>

* Don't keep constants

* Inline json name - property name comparison to util methods

* Remove unnecessary constructor keyword

* Consolidate non-null/missing property tests to parameterized suite

* Add custom json name tests for nonNull property checks

* Rename test to make maven happy

Maven won't run the test unless it ends with `Test` or `TestCase`

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

@@ -203,7 +203,7 @@ internal class AdapterGenerator(
           result.addStatement("%N = %N.fromJson(%N)",
               property.localName, nameAllocator[property.delegateKey], readerParam)
         } else {
-          val exception = unexpectedNull(property.localName, readerParam)
+          val exception = unexpectedNull(property, readerParam)
           result.addStatement("%N = %N.fromJson(%N) ?: throw·%L",
               property.localName, nameAllocator[property.delegateKey], readerParam, exception)
         }
@@ -221,7 +221,7 @@ internal class AdapterGenerator(
           result.addStatement("%L -> %N = %N.fromJson(%N)",
               propertyIndex, property.localName, nameAllocator[property.delegateKey], readerParam)
         } else {
-          val exception = unexpectedNull(property.localName, readerParam)
+          val exception = unexpectedNull(property, readerParam)
           result.addStatement("%L -> %N = %N.fromJson(%N) ?: throw·%L",
               propertyIndex, property.localName, nameAllocator[property.delegateKey], readerParam,
               exception)
@@ -308,7 +308,8 @@ internal class AdapterGenerator(
       }
       if (!property.isTransient && property.isRequired) {
         val missingPropertyBlock =
-            CodeBlock.of("%T.missingProperty(%S, %N)", Util::class, property.localName, readerParam)
+            CodeBlock.of("%T.missingProperty(%S, %S, %N)",
+                MOSHI_UTIL, property.localName, property.jsonName, readerParam)
         result.addCode(" ?: throw·%L", missingPropertyBlock)
       }
       separator = ",\n"
@@ -341,8 +342,9 @@ internal class AdapterGenerator(
     return result.build()
   }
 
-  private fun unexpectedNull(identifier: String, reader: ParameterSpec): CodeBlock {
+  private fun unexpectedNull(property: PropertyGenerator, reader: ParameterSpec): CodeBlock {
-    return CodeBlock.of("%T.unexpectedNull(%S, %N)", Util::class, identifier, reader)
+    return CodeBlock.of("%T.unexpectedNull(%S, %S, %N)",
+        MOSHI_UTIL, property.localName, property.jsonName, reader)
   }
 
   private fun generateToJsonFun(): FunSpec {

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

@@ -83,8 +83,11 @@ internal class KotlinJsonAdapter<T>(
       values[index] = binding.adapter.fromJson(reader)
 
       if (values[index] == null && !binding.property.returnType.isMarkedNullable) {
-        throw JsonDataException(
+        throw Util.unexpectedNull(
-            "Non-null value '${binding.property.name}' was null at ${reader.path}")
+            binding.property.name,
+            binding.jsonName,
+            reader
+        )
       }
     }
     reader.endObject()
@@ -93,8 +96,11 @@ internal class KotlinJsonAdapter<T>(
     for (i in 0 until constructorSize) {
       if (values[i] === ABSENT_VALUE && !constructor.parameters[i].isOptional) {
         if (!constructor.parameters[i].type.isMarkedNullable) {
-          throw JsonDataException(
+          throw Util.missingProperty(
-              "Required value '${constructor.parameters[i].name}' missing at ${reader.path}")
+              constructor.parameters[i].name,
+              bindings[i]?.jsonName,
+              reader
+          )
         }
         values[i] = null // Replace absent with null.
       }
@@ -130,6 +136,7 @@ internal class KotlinJsonAdapter<T>(
 
   data class Binding<K, P>(
       val name: String,
+      val jsonName: String?,
       val adapter: JsonAdapter<P>,
       val property: KProperty1<K, P>,
       val parameter: KParameter?) {
@@ -245,8 +252,13 @@ class KotlinJsonAdapterFactory : JsonAdapter.Factory {
           resolvedPropertyType, Util.jsonAnnotations(allAnnotations.toTypedArray()), property.name)
 
       @Suppress("UNCHECKED_CAST")
-      bindingsByName[property.name] = KotlinJsonAdapter.Binding(name, adapter,
+      bindingsByName[property.name] = KotlinJsonAdapter.Binding(
-          property as KProperty1<Any, Any?>, parameter)
+          name,
+          jsonAnnotation?.name ?: name,
+          adapter,
+          property as KProperty1<Any, Any?>,
+          parameter
+      )
     }
 
     val bindings = ArrayList<KotlinJsonAdapter.Binding<Any, Any?>?>()

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

@@ -0,0 +1,255 @@
+package com.squareup.moshi.kotlin
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonAdapter
+import com.squareup.moshi.JsonAdapter.Factory
+import com.squareup.moshi.JsonClass
+import com.squareup.moshi.JsonDataException
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.ToJson
+import com.squareup.moshi.Types
+import com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory
+import com.squareup.moshi.kotlin.reflect.adapter
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Assert.fail
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.Parameterized
+import org.junit.runners.Parameterized.Parameters
+import java.lang.reflect.Type
+import kotlin.annotation.AnnotationRetention.RUNTIME
+
+/**
+ * Parameterized tests that test serialization with both [KotlinJsonAdapterFactory] and code gen.
+ */
+@RunWith(Parameterized::class)
+class DualKotlinTest(useReflection: Boolean) {
+
+  companion object {
+    @Parameters(name = "reflective={0}")
+    @JvmStatic
+    fun parameters(): List<Array<*>> {
+      return listOf(
+          arrayOf(true),
+          arrayOf(false)
+      )
+    }
+  }
+
+  @Suppress("UNCHECKED_CAST")
+  private val moshi = Moshi.Builder()
+      .apply {
+        if (useReflection) {
+          add(KotlinJsonAdapterFactory())
+          add(object : Factory {
+            override fun create(
+                type: Type,
+                annotations: MutableSet<out Annotation>,
+                moshi: Moshi
+            ): JsonAdapter<*>? {
+              // Prevent falling back to generated adapter lookup
+              val rawType = Types.getRawType(type)
+              val metadataClass = Class.forName("kotlin.Metadata") as Class<out Annotation>
+              check(!rawType.isAnnotationPresent(metadataClass)) {
+                "Unhandled Kotlin type in reflective test! $rawType"
+              }
+              return moshi.nextAdapter<Any>(this, type, annotations)
+            }
+          })
+        }
+      }
+      .build()
+
+
+  @Test fun requiredValueAbsent() {
+    val jsonAdapter = moshi.adapter<RequiredValueAbsent>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("""{"a":4}""")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Required value 'b' missing at $")
+    }
+  }
+
+  @JsonClass(generateAdapter = true)
+  class RequiredValueAbsent(var a: Int = 3, var b: Int)
+
+  @Test fun requiredValueWithDifferentJsonNameAbsent() {
+    val jsonAdapter = moshi.adapter<RequiredValueWithDifferentJsonNameAbsent>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("""{"a":4}""")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Required value 'b' (JSON name 'bPrime') missing at \$")
+    }
+  }
+
+  @JsonClass(generateAdapter = true)
+  class RequiredValueWithDifferentJsonNameAbsent(var a: Int = 3, @Json(name = "bPrime") var b: Int)
+
+  @Test fun nonNullPropertySetToNullFailsWithJsonDataException() {
+    val jsonAdapter = moshi.adapter<HasNonNullProperty>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("{\"a\":null}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
+    }
+  }
+
+  @Test fun nonNullPropertySetToNullFromAdapterFailsWithJsonDataException() {
+    val jsonAdapter = moshi.newBuilder()
+        .add(object {
+          @Suppress("UNUSED_PARAMETER")
+          @FromJson
+          fun fromJson(string: String): String? = null
+        })
+        .build()
+        .adapter<HasNonNullProperty>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("{\"a\":\"hello\"}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
+    }
+  }
+
+  @JsonClass(generateAdapter = true)
+  class HasNonNullProperty {
+    var a: String = ""
+  }
+
+  @Test fun nonNullPropertyWithJsonNameSetToNullFailsWithJsonDataException() {
+    val jsonAdapter = moshi.adapter<HasNonNullPropertyDifferentJsonName>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("{\"aPrime\":null}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' (JSON name 'aPrime') was null at \$.aPrime")
+    }
+  }
+
+  @Test fun nonNullPropertyWithJsonNameSetToNullFromAdapterFailsWithJsonDataException() {
+    val jsonAdapter = moshi.newBuilder()
+        .add(object {
+          @Suppress("UNUSED_PARAMETER")
+          @FromJson
+          fun fromJson(string: String): String? = null
+        })
+        .build()
+        .adapter<HasNonNullPropertyDifferentJsonName>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("{\"aPrime\":\"hello\"}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' (JSON name 'aPrime') was null at \$.aPrime")
+    }
+  }
+
+  @JsonClass(generateAdapter = true)
+  class HasNonNullPropertyDifferentJsonName {
+    @Json(name = "aPrime") var a: String = ""
+  }
+
+  @Test fun nonNullConstructorParameterCalledWithNullFailsWithJsonDataException() {
+    val jsonAdapter = moshi.adapter<HasNonNullConstructorParameter>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("{\"a\":null}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
+    }
+  }
+
+  @Test fun nonNullConstructorParameterCalledWithNullFromAdapterFailsWithJsonDataException() {
+    val jsonAdapter = moshi.newBuilder()
+        .add(object {
+          @Suppress("UNUSED_PARAMETER")
+          @FromJson
+          fun fromJson(string: String): String? = null
+        })
+        .build()
+        .adapter<HasNonNullConstructorParameter>()
+
+    try {
+      //language=JSON
+      jsonAdapter.fromJson("{\"a\":\"hello\"}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
+    }
+  }
+
+  @Retention(RUNTIME)
+  annotation class Nullable
+
+  @JsonClass(generateAdapter = true)
+  data class HasNonNullConstructorParameter(val a: String)
+
+  @JsonClass(generateAdapter = true)
+  data class HasNullableConstructorParameter(val a: String?)
+
+  @Test fun delegatesToInstalledAdaptersBeforeNullChecking() {
+    val localMoshi = moshi.newBuilder()
+        .add(object {
+          @FromJson
+          fun fromJson(@Nullable string: String?): String {
+            return string ?: "fallback"
+          }
+
+          @ToJson
+          fun toJson(@Nullable value: String?): String {
+            return value ?: "fallback"
+          }
+        })
+        .build()
+
+    val hasNonNullConstructorParameterAdapter =
+        localMoshi.adapter<HasNonNullConstructorParameter>()
+    assertThat(hasNonNullConstructorParameterAdapter
+        //language=JSON
+        .fromJson("{\"a\":null}")).isEqualTo(HasNonNullConstructorParameter("fallback"))
+
+    val hasNullableConstructorParameterAdapter =
+        localMoshi.adapter<HasNullableConstructorParameter>()
+    assertThat(hasNullableConstructorParameterAdapter
+        //language=JSON
+        .fromJson("{\"a\":null}")).isEqualTo(HasNullableConstructorParameter("fallback"))
+    assertThat(hasNullableConstructorParameterAdapter
+        //language=JSON
+        .toJson(HasNullableConstructorParameter(null))).isEqualTo("{\"a\":\"fallback\"}")
+  }
+
+  @JsonClass(generateAdapter = true)
+  data class HasNullableTypeWithGeneratedAdapter(val a: HasNonNullConstructorParameter?)
+
+  @Test fun delegatesToInstalledAdaptersBeforeNullCheckingWithGeneratedAdapter() {
+    val adapter = moshi.adapter<HasNullableTypeWithGeneratedAdapter>()
+
+    val encoded = HasNullableTypeWithGeneratedAdapter(null)
+    //language=JSON
+    assertThat(adapter.toJson(encoded)).isEqualTo("""{}""")
+    //language=JSON
+    assertThat(adapter.serializeNulls().toJson(encoded)).isEqualTo("""{"a":null}""")
+
+    //language=JSON
+    val decoded = adapter.fromJson("""{"a":null}""")!!
+    assertThat(decoded.a).isEqualTo(null)
+  }
+
+}

kotlin/tests/src/test/kotlin/com/squareup/moshi/kotlin/codegen/GeneratedAdaptersTest.kt

@@ -410,53 +410,6 @@ class GeneratedAdaptersTest {
   @JsonClass(generateAdapter = true)
   class ConstructorDefaultValues(var a: Int = -1, var b: Int = -2)
 
-  @Test fun requiredValueAbsent() {
-    val moshi = Moshi.Builder().build()
-    val jsonAdapter = moshi.adapter<RequiredValueAbsent>()
-
-    try {
-      jsonAdapter.fromJson("""{"a":4}""")
-      fail()
-    } catch(expected: JsonDataException) {
-      assertThat(expected).hasMessage("Required property 'b' missing at \$")
-    }
-  }
-
-  @JsonClass(generateAdapter = true)
-  class RequiredValueAbsent(var a: Int = 3, var b: Int)
-
-  @Test fun nonNullConstructorParameterCalledWithNullFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().build()
-    val jsonAdapter = moshi.adapter<HasNonNullConstructorParameter>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":null}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  @Test fun nonNullConstructorParameterCalledWithNullFromAdapterFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().add(object {
-      @FromJson fun fromJson(string: String): String? = null
-    }).build()
-    val jsonAdapter = moshi.adapter<HasNonNullConstructorParameter>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":\"hello\"}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  @JsonClass(generateAdapter = true)
-  data class HasNonNullConstructorParameter(val a: String)
-
-  @JsonClass(generateAdapter = true)
-  data class HasNullableConstructorParameter(val a: String?)
-
   @Test fun explicitNull() {
     val moshi = Moshi.Builder().build()
     val jsonAdapter = moshi.adapter<ExplicitNull>()
@@ -610,37 +563,6 @@ class GeneratedAdaptersTest {
     }
   }
 
-  @Test fun nonNullPropertySetToNullFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().build()
-    val jsonAdapter = moshi.adapter<HasNonNullProperty>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":null}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  @Test fun nonNullPropertySetToNullFromAdapterFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().add(object {
-      @FromJson fun fromJson(string: String): String? = null
-    }).build()
-    val jsonAdapter = moshi.adapter<HasNonNullProperty>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":\"hello\"}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  @JsonClass(generateAdapter = true)
-  class HasNonNullProperty {
-    var a: String = ""
-  }
-
   @Test fun manyProperties32() {
     val moshi = Moshi.Builder().build()
     val jsonAdapter = moshi.adapter<ManyProperties32>()
@@ -1114,62 +1036,11 @@ class GeneratedAdaptersTest {
 
   @Test fun adaptersAreNullSafe() {
     val moshi = Moshi.Builder().build()
-    val adapter = moshi.adapter<HasNonNullConstructorParameter>()
+    val adapter = moshi.adapter<HasNullableBoolean>()
     assertThat(adapter.fromJson("null")).isNull()
     assertThat(adapter.toJson(null)).isEqualTo("null")
   }
 
-  @Retention(AnnotationRetention.RUNTIME)
-  annotation class Nullable
-
-  @Test fun delegatesToInstalledAdaptersBeforeNullChecking() {
-    val moshi = Moshi.Builder()
-        .add(object {
-          @FromJson fun fromJson(@Nullable string: String?): String {
-            return string ?: "fallback"
-          }
-
-          @ToJson fun toJson(@Nullable value: String?): String {
-            return value ?: "fallback"
-          }
-        })
-        .build()
-
-    val hasNonNullConstructorParameterAdapter =
-        moshi.adapter<HasNonNullConstructorParameter>()
-    assertThat(hasNonNullConstructorParameterAdapter
-        .fromJson("{\"a\":null}")).isEqualTo(
-        HasNonNullConstructorParameter(
-            "fallback"))
-
-    val hasNullableConstructorParameterAdapter =
-        moshi.adapter<HasNullableConstructorParameter>()
-    assertThat(hasNullableConstructorParameterAdapter
-        .fromJson("{\"a\":null}")).isEqualTo(
-        HasNullableConstructorParameter(
-            "fallback"))
-    assertThat(hasNullableConstructorParameterAdapter
-        .toJson(
-            HasNullableConstructorParameter(
-                null))).isEqualTo("{\"a\":\"fallback\"}")
-  }
-
-  @JsonClass(generateAdapter = true)
-  data class HasNullableTypeWithGeneratedAdapter(val a: HasNonNullConstructorParameter?)
-
-  @Test fun delegatesToInstalledAdaptersBeforeNullCheckingWithGeneratedAdapter() {
-    val moshi = Moshi.Builder().build()
-    val adapter = moshi.adapter<HasNullableTypeWithGeneratedAdapter>()
-
-    val encoded = HasNullableTypeWithGeneratedAdapter(
-        null)
-    assertThat(adapter.toJson(encoded)).isEqualTo("""{}""")
-    assertThat(adapter.serializeNulls().toJson(encoded)).isEqualTo("""{"a":null}""")
-
-    val decoded = adapter.fromJson("""{"a":null}""")!!
-    assertThat(decoded.a).isEqualTo(null)
-  }
-
   @JsonClass(generateAdapter = true)
   data class HasCollectionOfPrimitives(val listOfInts: List<Int>)
 

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

@@ -133,80 +133,6 @@ class KotlinJsonAdapterTest {
 
   class ConstructorDefaultValues(var a: Int = -1, var b: Int = -2)
 
-  @Test fun requiredValueAbsent() {
-    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter<RequiredValueAbsent>()
-
-    try {
-      jsonAdapter.fromJson("""{"a":4}""")
-      fail()
-    } catch(expected: JsonDataException) {
-      assertThat(expected).hasMessage("Required value 'b' missing at $")
-    }
-  }
-
-  class RequiredValueAbsent(var a: Int = 3, var b: Int)
-
-  @Test fun nonNullConstructorParameterCalledWithNullFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter<HasNonNullConstructorParameter>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":null}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  @Test fun nonNullConstructorParameterCalledWithNullFromAdapterFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().add(object {
-      @FromJson fun fromJson(string: String): String? = null
-    }).add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter<HasNonNullConstructorParameter>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":\"hello\"}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  data class HasNonNullConstructorParameter(val a: String)
-
-  data class HasNullableConstructorParameter(val a: String?)
-
-  @Test fun nonNullPropertySetToNullFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter<HasNonNullProperty>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":null}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  @Test fun nonNullPropertySetToNullFromAdapterFailsWithJsonDataException() {
-    val moshi = Moshi.Builder().add(object {
-      @FromJson fun fromJson(string: String): String? = null
-    }).add(KotlinJsonAdapterFactory()).build()
-    val jsonAdapter = moshi.adapter<HasNonNullProperty>()
-
-    try {
-      jsonAdapter.fromJson("{\"a\":\"hello\"}")
-      fail()
-    } catch (expected: JsonDataException) {
-      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
-    }
-  }
-
-  class HasNonNullProperty {
-    var a: String = ""
-  }
-
   @Test fun duplicatedValueParameter() {
     val moshi = Moshi.Builder().add(KotlinJsonAdapterFactory()).build()
     val jsonAdapter = moshi.adapter<DuplicateValueParameter>()
@@ -875,32 +801,6 @@ class KotlinJsonAdapterTest {
     assertThat(adapter.toJson(value)).isEqualTo(json)
   }
 
-  @Retention(RUNTIME)
-  annotation class Nullable
-
-  @Test fun delegatesToInstalledAdaptersBeforeNullChecking() {
-    val moshi = Moshi.Builder()
-        .add(object {
-          @FromJson fun fromJson(@Nullable string: String?): String {
-            return string ?: "fallback"
-          }
-
-          @ToJson fun toJson(@Nullable value: String?): String {
-            return value ?: "fallback"
-          }
-        })
-        .add(KotlinJsonAdapterFactory())
-        .build()
-
-    assertThat(moshi.adapter<HasNonNullConstructorParameter>()
-        .fromJson("{\"a\":null}")).isEqualTo(HasNonNullConstructorParameter("fallback"))
-
-    assertThat(moshi.adapter<HasNullableConstructorParameter>()
-        .fromJson("{\"a\":null}")).isEqualTo(HasNullableConstructorParameter("fallback"))
-    assertThat(moshi.adapter<HasNullableConstructorParameter>()
-        .toJson(HasNullableConstructorParameter(null))).isEqualTo("{\"a\":\"fallback\"}")
-  }
-
   @Test fun mixingReflectionAndCodegen() {
     val moshi = Moshi.Builder()
         .add(KotlinJsonAdapterFactory())
@@ -970,7 +870,7 @@ class KotlinJsonAdapterTest {
         .build()
 
     // TODO in CR: We had to mark this as nullable, vs before the jsonadapter factory would always run
-    val adapter = moshi.adapter<HasNonNullConstructorParameter?>()
+    val adapter = moshi.adapter<HasNullableBoolean?>()
     assertThat(adapter.fromJson("null")).isNull()
     assertThat(adapter.toJson(null)).isEqualTo("null")
   }

moshi/src/main/java/com/squareup/moshi/internal/Util.java

@@ -44,8 +44,6 @@ import static com.squareup.moshi.Types.subtypeOf;
 import static com.squareup.moshi.Types.supertypeOf;
 
 public final class Util {
-  private static final String REQUIRED_PROPERTY_TEMPLATE = "Required property '%s' missing at %s";
-  private static final String UNEXPECTED_NULL_TEMPLATE = "Non-null value '%s' was null at %s";
   public static final Set<Annotation> NO_ANNOTATIONS = Collections.emptySet();
   public static final Type[] EMPTY_TYPE_ARRAY = new Type[] {};
   @Nullable private static final Class<?> DEFAULT_CONSTRUCTOR_MARKER;
@@ -567,17 +565,35 @@ public final class Util {
     throw new IllegalStateException("No defaults constructor found for " + targetClass);
   }
 
-  public static JsonDataException missingProperty(String property, JsonReader reader) {
+  public static JsonDataException missingProperty(
-    return jsonDataException(REQUIRED_PROPERTY_TEMPLATE, property, reader);
+      String propertyName,
+      String jsonName,
+      JsonReader reader
+  ) {
+    String path = reader.getPath();
+    String message;
+    if (jsonName.equals(propertyName)) {
+      message = String.format("Required value '%s' missing at %s", propertyName, path);
+    } else {
+      message = String.format("Required value '%s' (JSON name '%s') missing at %s",
+          propertyName, jsonName, path);
+    }
+    return new JsonDataException(message);
   }
 
-  public static JsonDataException unexpectedNull(String property, JsonReader reader) {
+  public static JsonDataException unexpectedNull(
-    return jsonDataException(UNEXPECTED_NULL_TEMPLATE, property, reader);
+      String propertyName,
+      String jsonName,
+      JsonReader reader
+  ) {
+    String path = reader.getPath();
+    String message;
+    if (jsonName.equals(propertyName)) {
+      message = String.format("Non-null value '%s' was null at %s", propertyName, path);
+    } else {
+      message = String.format("Non-null value '%s' (JSON name '%s') was null at %s",
+          propertyName, jsonName, path);
     }
-
+    return new JsonDataException(message);
-  private static JsonDataException jsonDataException(
-      String template, String property, JsonReader reader) {
-    return new JsonDataException(
-        String.format(template, property, reader.getPath()));
   }
 }