KotlinJsonAdapter (#281)

* Add kotlin-module with support for Kotlin data classes

* Naming and style changes to KotlinJsonAdapter.

Biggest changes:

 * Attempt to support regular classes and data classes
 * Avoid parameter hashing when indexing is sufficient for
   constructor parameters

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

@@ -105,19 +105,6 @@ final class ClassJsonAdapter<T> extends JsonAdapter<T> {
       }
     }
 
-    /**
-     * Returns true if {@code rawType} is built in. We don't reflect on private fields of platform
-     * types because they're unspecified and likely to be different on Java vs. Android.
-     */
-    private boolean isPlatformType(Class<?> rawType) {
-      String name = rawType.getName();
-      return name.startsWith("android.")
-          || name.startsWith("java.")
-          || name.startsWith("javax.")
-          || name.startsWith("kotlin.")
-          || name.startsWith("scala.");
-    }
-
     /** Returns true if fields with {@code modifiers} are included in the emitted JSON. */
     private boolean includeField(boolean platformType, int modifiers) {
       if (Modifier.isStatic(modifiers) || Modifier.isTransient(modifiers)) return false;
@@ -125,6 +112,19 @@ final class ClassJsonAdapter<T> extends JsonAdapter<T> {
     }
   };
 
+  /**
+   * Returns true if {@code rawType} is built in. We don't reflect on private fields of platform
+   * types because they're unspecified and likely to be different on Java vs. Android.
+   */
+  static boolean isPlatformType(Class<?> rawType) {
+    String name = rawType.getName();
+    return name.startsWith("android.")
+        || name.startsWith("java.")
+        || name.startsWith("javax.")
+        || name.startsWith("kotlin.")
+        || name.startsWith("scala.");
+  }
+
   private final ClassFactory<T> classFactory;
   private final FieldBinding<?>[] fieldsArray;
   private final JsonReader.Options options;

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

@@ -19,12 +19,23 @@ import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 
-import static java.lang.annotation.ElementType.FIELD;
-import static java.lang.annotation.ElementType.METHOD;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
-/** Customizes how a field is encoded as JSON. */
-@Target({FIELD, METHOD})
+/**
+ * Customizes how a field is encoded as JSON.
+ *
+ * <p>Although this annotation doesn't declare a {@link Target}, it is only honored in the following
+ * elements:
+ *
+ * <ul>
+ *   <li><strong>Java class fields</strong>
+ *   <li><strong>Kotlin properties</strong> for use with {@code moshi-kotlin}. 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
+ * Extension</a> may also use this annotation on abstract getters.
+ */
 @Retention(RUNTIME)
 @Documented
 public @interface Json {

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

@@ -533,15 +533,6 @@ public final class MoshiTest {
   }
 
   @Test public void addNullFails() throws Exception {
-    JsonAdapter jsonAdapter = new JsonAdapter() {
-      @Override public Object fromJson(JsonReader reader) throws IOException {
-        throw new AssertionError();
-      }
-
-      @Override public void toJson(JsonWriter writer, Object value) throws IOException {
-        throw new AssertionError();
-      }
-    };
     Type type = Object.class;
     Class<? extends Annotation> annotation = Annotation.class;
     Moshi.Builder builder = new Moshi.Builder();