Kotlin-reflect QoL APIs (#875)

* Start MoshiKotlinExtensions

* Add Moshi.Builder.add() with reified typeOf

* Use non-shadowing name for addAdapter

* Implement KType.toType()

.javaType isn't implemented

* Don't re-wrap wrapped adapters

* Use new adapter functions in tests to smoke test

* Don't enable uses experimental in kotlin-reflect, only the test

* Use internal leniency API

* Use toType in addAdapter too

* Update error message in test

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

@@ -15,6 +15,7 @@
  */
 package com.squareup.moshi;
 
+import com.squareup.moshi.internal.NonNullJsonAdapter;
 import com.squareup.moshi.internal.NullSafeJsonAdapter;
 import java.io.IOException;
 import java.lang.annotation.Annotation;
@@ -140,29 +141,7 @@ public abstract class JsonAdapter<T> {
    * handled elsewhere. This should only be used to fail on explicit nulls.
    */
   @CheckReturnValue public final JsonAdapter<T> nonNull() {
-    final JsonAdapter<T> delegate = this;
-    return new JsonAdapter<T>() {
-      @Override public @Nullable T fromJson(JsonReader reader) throws IOException {
-        if (reader.peek() == JsonReader.Token.NULL) {
-          throw new JsonDataException("Unexpected null at " + reader.getPath());
-        } else {
-          return delegate.fromJson(reader);
-        }
-      }
-      @Override public void toJson(JsonWriter writer, @Nullable T value) throws IOException {
-        if (value == null) {
-          throw new JsonDataException("Unexpected null at " + writer.getPath());
-        } else {
-          delegate.toJson(writer, value);
-        }
-      }
-      @Override boolean isLenient() {
-        return delegate.isLenient();
-      }
-      @Override public String toString() {
-        return delegate + ".nonNull()";
-      }
-    };
+    return new NonNullJsonAdapter<>(this);
   }
 
   /** Returns a JSON adapter equal to this, but is lenient when reading and writing. */

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

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2019 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.squareup.moshi.internal;
+
+import com.squareup.moshi.JsonAdapter;
+import com.squareup.moshi.JsonDataException;
+import com.squareup.moshi.JsonReader;
+import com.squareup.moshi.JsonWriter;
+import java.io.IOException;
+import javax.annotation.Nullable;
+
+public final class NonNullJsonAdapter<T> extends JsonAdapter<T> {
+
+  private final JsonAdapter<T> delegate;
+
+  public NonNullJsonAdapter(JsonAdapter<T> delegate) {
+    this.delegate = delegate;
+  }
+
+  public JsonAdapter<T> delegate() {
+    return delegate;
+  }
+
+  @Nullable
+  @Override
+  public T fromJson(JsonReader reader) throws IOException {
+    if (reader.peek() == JsonReader.Token.NULL) {
+      throw new JsonDataException("Unexpected null at " + reader.getPath());
+    } else {
+      return delegate.fromJson(reader);
+    }
+  }
+
+  @Override
+  public void toJson(JsonWriter writer, @Nullable T value) throws IOException {
+    if (value == null) {
+      throw new JsonDataException("Unexpected null at " + writer.getPath());
+    } else {
+      delegate.toJson(writer, value);
+    }
+  }
+
+  @Override
+  public String toString() {
+    return delegate + ".nonNull()";
+  }
+}

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

@@ -282,7 +282,7 @@ public final class JsonAdapterTest {
       @Override public void toJson(JsonWriter writer, @Nullable Boolean value) throws IOException {
         throw new AssertionError();
       }
-    }.lenient().nonNull();
+    }.lenient().serializeNulls();
     assertThat(adapter.fromJson("true true")).isEqualTo(true);
   }
 }