Implement reflective support for Java Records (#1381)

* Standardize around JDK 8

* Update GJF to support newer JDKs

* Fix misc java 8 issues in tests

* Prepare java 16/records checking at runtime

* Implement real RecordJsonAdapter

* Spotless

* Prepare build for JDK 16+

* Fix property name for kapt

* Small cleanup

* Make FallbackEnum java-8 happy

* Remove animalsniffer

* Fix format

* Add opens for ExtendsPlatformClassWithProtectedFields

* Return null every time in shim for main tests

* Use JDK 16 + release 8 to replace animalsniffer

* Simplify accessor accessible handling

* Remove manifest attrs

* Fix typo

* Fix KCT tests + upgrade it

* Cover another

* Try explicit kotlin daemon args for java 17?

* Disable 17-ea for now until kotlin 1.5.30

* Add JsonQualifier and Json(name) tests + fix qualifiers

* Ensure constructor is accessible

* GJF it properly

* GJF 1.11

* Unwrap InvocationTargetException

* Use MethodHandle for constructor

* Use MethodHandle for accessor too

* Revert "Remove manifest attrs"

This reverts commit 3eb768fd6904bb5c979aa01c3c182e0fb9329d62.

* Proper MR jar

* *actually* fix GJF, which wasn't getting applied before

We can just enable this everywhere now since we require JDK 16 anyway

* Make IDE happy about modules access

* Fixup records tests to play nice with modules

Gotta be public

* Add complex smoke test

* Remove comment

Not a regression test in this case

.github/workflows/build.yml

@@ -10,14 +10,7 @@ jobs:
       fail-fast: false
       matrix:
         java-version:
-          - 8
-          - 9
-          - 10
-          - 11
-          - 12
-          - 13
-          - 14
-          - 15
+          - 16
 
     steps:
       - name: Checkout
@@ -46,7 +39,7 @@ jobs:
         run: ./gradlew build check --stacktrace
 
       - name: Publish (default branch only)
-        if: github.repository == 'square/moshi' && github.ref == 'refs/heads/master' && matrix.java-version == '8'
+        if: github.repository == 'square/moshi' && github.ref == 'refs/heads/master' && matrix.java-version == '16'
         run: ./gradlew uploadArchives
         env:
           ORG_GRADLE_PROJECT_SONATYPE_NEXUS_USERNAME: ${{ secrets.SONATYPE_NEXUS_USERNAME }}

adapters/build.gradle.kts

@@ -14,18 +14,9 @@
  * limitations under the License.
  */
 
-import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
-
 plugins {
   kotlin("jvm")
   id("com.vanniktech.maven.publish")
-  id("ru.vyarus.animalsniffer")
-}
-
-tasks.withType<KotlinCompile>().configureEach {
-  kotlinOptions {
-    jvmTarget = "1.6"
-  }
 }
 
 dependencies {

build.gradle.kts

@@ -33,7 +33,6 @@ plugins {
   id("com.vanniktech.maven.publish") version "0.14.2" apply false
   id("org.jetbrains.dokka") version "1.4.32" apply false
   id("com.diffplug.spotless") version "5.12.4"
-  id("ru.vyarus.animalsniffer") version "1.5.3" apply false
   id("me.champeau.gradle.japicmp") version "0.2.9" apply false
 }
 
@@ -44,8 +43,6 @@ spotless {
     indentWithSpaces(2)
     endWithNewline()
   }
-  // GJF not compatible with JDK 15 yet
-  if (!JavaVersion.current().isCompatibleWith(JavaVersion.VERSION_15)) {
   val externalJavaFiles = arrayOf(
     "**/ClassFactory.java",
     "**/Iso8601Utils.java",
@@ -70,7 +67,7 @@ spotless {
     "**/TypesTest.java"
   )
   val configureCommonJavaFormat: JavaExtension.() -> Unit = {
-      googleJavaFormat("1.7")
+    googleJavaFormat("1.11.0")
   }
   java {
     configureCommonJavaFormat()
@@ -88,7 +85,6 @@ spotless {
     configureCommonJavaFormat()
     target(*externalJavaFiles)
   }
-  }
   kotlin {
     ktlint(Dependencies.ktlintVersion).userData(mapOf("indent_size" to "2"))
     target("**/*.kt")
@@ -129,15 +125,14 @@ subprojects {
   // Apply with "java" instead of just "java-library" so kotlin projects get it too
   pluginManager.withPlugin("java") {
     configure<JavaPluginExtension> {
-      sourceCompatibility = JavaVersion.VERSION_1_7
-      targetCompatibility = JavaVersion.VERSION_1_7
+      toolchain {
+        languageVersion.set(JavaLanguageVersion.of(16))
       }
     }
-
-  pluginManager.withPlugin("ru.vyarus.animalsniffer") {
-    dependencies {
-      "compileOnly"(Dependencies.AnimalSniffer.annotations)
-      "signature"(Dependencies.AnimalSniffer.java7Signature)
+    if (project.name != "records-tests") {
+      tasks.withType<JavaCompile>().configureEach {
+        options.release.set(8)
+      }
     }
   }
 
@@ -146,6 +141,7 @@ subprojects {
       kotlinOptions {
         @Suppress("SuspiciousCollectionReassignment")
         freeCompilerArgs += listOf("-progressive")
+        jvmTarget = "1.8"
       }
     }
 

buildSrc/src/main/kotlin/Dependencies.kt

@@ -21,11 +21,6 @@ object Dependencies {
   const val ktlintVersion = "0.41.0"
   const val okio = "com.squareup.okio:okio:2.10.0"
 
-  object AnimalSniffer {
-    const val annotations = "org.codehaus.mojo:animal-sniffer-annotations:1.16"
-    const val java7Signature = "org.codehaus.mojo.signature:java17:1.0@signature"
-  }
-
   object AutoService {
     private const val version = "1.0"
     const val annotations = "com.google.auto.service:auto-service-annotations:$version"
@@ -53,7 +48,7 @@ object Dependencies {
 
   object Testing {
     const val assertj = "org.assertj:assertj-core:3.11.1"
-    const val compileTesting = "com.github.tschuchortdev:kotlin-compile-testing:1.4.0"
+    const val compileTesting = "com.github.tschuchortdev:kotlin-compile-testing:1.4.3"
     const val junit = "junit:junit:4.13.2"
     const val truth = "com.google.truth:truth:1.0.1"
   }

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

@@ -58,9 +58,9 @@ final class FallbackEnum {
             if (!(annotation instanceof Fallback)) {
               return null;
             }
-            Class<Enum> enumType = (Class<Enum>) rawType;
-            Enum<?> fallback = Enum.valueOf(enumType, ((Fallback) annotation).value());
-            return new FallbackEnumJsonAdapter<>(enumType, fallback);
+            //noinspection rawtypes
+            return new FallbackEnumJsonAdapter<>(
+                (Class<? extends Enum>) rawType, ((Fallback) annotation).value());
           }
         };
 
@@ -70,9 +70,9 @@ final class FallbackEnum {
     final JsonReader.Options options;
     final T defaultValue;
 
-    FallbackEnumJsonAdapter(Class<T> enumType, T defaultValue) {
+    FallbackEnumJsonAdapter(Class<T> enumType, String fallbackName) {
       this.enumType = enumType;
-      this.defaultValue = defaultValue;
+      this.defaultValue = Enum.valueOf(enumType, fallbackName);
       try {
         constants = enumType.getEnumConstants();
         nameStrings = new String[constants.length];

gradle.properties

@@ -15,9 +15,36 @@
 #
 
 # For Dokka https://github.com/Kotlin/dokka/issues/1405
-org.gradle.jvmargs=-XX:MaxMetaspaceSize=512m
+org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8 \
+  --add-opens=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.jvm=ALL-UNNAMED  \
+  --add-opens=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
 
-kapt.includeCompileClasspath=false
+# TODO move this to DSL in Kotlin 1.5.30 https://youtrack.jetbrains.com/issue/KT-44266
+kotlin.daemon.jvmargs=-Dfile.encoding=UTF-8 \
+  --add-opens=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.jvm=ALL-UNNAMED  \
+  --add-opens=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED \
+  --add-opens=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \
+  --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
+
+kapt.include.compile.classpath=false
 
 GROUP=com.squareup.moshi
 VERSION_NAME=1.13.0-SNAPSHOT

kotlin/codegen/build.gradle.kts

@@ -27,7 +27,6 @@ plugins {
 
 tasks.withType<KotlinCompile>().configureEach {
   kotlinOptions {
-    jvmTarget = "1.8"
     @Suppress("SuspiciousCollectionReassignment")
     freeCompilerArgs += listOf(
       "-Xopt-in=com.squareup.kotlinpoet.metadata.KotlinPoetMetadataPreview"
@@ -35,10 +34,20 @@ tasks.withType<KotlinCompile>().configureEach {
   }
 }
 
-// To make Gradle happy
-java {
-  sourceCompatibility = JavaVersion.VERSION_1_8
-  targetCompatibility = JavaVersion.VERSION_1_8
+tasks.withType<Test>().configureEach {
+  // For kapt to work with kotlin-compile-testing
+  jvmArgs(
+    "--add-opens=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.jvm=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED",
+    "--add-opens=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED",
+  )
 }
 
 val shade: Configuration = configurations.maybeCreate("compileShaded")

kotlin/tests/build.gradle.kts

@@ -21,6 +21,11 @@ plugins {
   kotlin("kapt")
 }
 
+tasks.withType<Test>().configureEach {
+  // ExtendsPlatformClassWithProtectedField tests a case where we set a protected ByteArrayOutputStream.buf field
+  jvmArgs("--add-opens=java.base/java.io=ALL-UNNAMED")
+}
+
 tasks.withType<KotlinCompile>().configureEach {
   kotlinOptions {
     @Suppress("SuspiciousCollectionReassignment")

moshi/build.gradle.kts

@@ -19,14 +19,49 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 plugins {
   kotlin("jvm")
   id("com.vanniktech.maven.publish")
-  id("ru.vyarus.animalsniffer")
+}
+
+val mainSourceSet by sourceSets.named("main")
+val java16 by sourceSets.creating {
+  java {
+    srcDir("src/main/java16")
+  }
+}
+
+tasks.named<JavaCompile>("compileJava16Java") {
+  javaCompiler.set(
+    javaToolchains.compilerFor {
+      languageVersion.set(JavaLanguageVersion.of(16))
+    }
+  )
+  options.release.set(16)
+}
+
+// Package our actual RecordJsonAdapter from java16 sources in and denote it as an MRJAR
+tasks.named<Jar>("jar") {
+  from(java16.output) {
+    into("META-INF/versions/16")
+  }
+  manifest {
+    attributes("Multi-Release" to "true")
+  }
+}
+
+configurations {
+  "java16Implementation" {
+    extendsFrom(api.get())
+    extendsFrom(implementation.get())
+  }
+}
+
+tasks.withType<Test>().configureEach {
+  // ExtendsPlatformClassWithProtectedField tests a case where we set a protected ByteArrayOutputStream.buf field
+  jvmArgs("--add-opens=java.base/java.io=ALL-UNNAMED")
 }
 
 tasks.withType<KotlinCompile>()
   .configureEach {
     kotlinOptions {
-      jvmTarget = "1.6"
-
       if (name.contains("test", true)) {
         @Suppress("SuspiciousCollectionReassignment") // It's not suspicious
         freeCompilerArgs += listOf("-Xopt-in=kotlin.ExperimentalStdlibApi")
@@ -35,6 +70,8 @@ tasks.withType<KotlinCompile>()
   }
 
 dependencies {
+  // So the j16 source set can "see" main Moshi sources
+  "java16Implementation"(mainSourceSet.output)
   compileOnly(Dependencies.jsr305)
   api(Dependencies.okio)
 

moshi/records-tests/build.gradle.kts

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2021 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
+ *
+ *    https://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.
+ */
+
+plugins {
+  `java-library`
+}
+
+tasks.withType<JavaCompile>().configureEach {
+  options.release.set(16)
+}
+
+dependencies {
+  testImplementation(project(":moshi"))
+  testCompileOnly(Dependencies.jsr305)
+  testImplementation(Dependencies.Testing.junit)
+  testImplementation(Dependencies.Testing.truth)
+}

moshi/records-tests/src/test/java/com/squareup/moshi/records/RecordsTest.java

@@ -0,0 +1,195 @@
+/*
+ * Copyright (C) 2021 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
+ *
+ *    https://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.records;
+
+import static com.google.common.truth.Truth.assertThat;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import com.squareup.moshi.FromJson;
+import com.squareup.moshi.Json;
+import com.squareup.moshi.JsonQualifier;
+import com.squareup.moshi.Moshi;
+import com.squareup.moshi.ToJson;
+import com.squareup.moshi.Types;
+import java.io.IOException;
+import java.lang.annotation.Retention;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import org.junit.Test;
+
+public final class RecordsTest {
+
+  private final Moshi moshi = new Moshi.Builder().build();
+
+  @Test
+  public void smokeTest() throws IOException {
+    var stringAdapter = moshi.adapter(String.class);
+    var adapter =
+        moshi
+            .newBuilder()
+            .add(CharSequence.class, stringAdapter)
+            .add(Types.subtypeOf(CharSequence.class), stringAdapter)
+            .add(Types.supertypeOf(CharSequence.class), stringAdapter)
+            .build()
+            .adapter(SmokeTestType.class);
+    var instance =
+        new SmokeTestType(
+            "John",
+            "Smith",
+            25,
+            List.of("American"),
+            70.5f,
+            null,
+            true,
+            List.of("super wildcards!"),
+            List.of("extend wildcards!"),
+            List.of("unbounded"),
+            List.of("objectList"),
+            new int[] {1, 2, 3},
+            new String[] {"fav", "arrays"},
+            Map.of("italian", "pasta"),
+            Set.of(List.of(Map.of("someKey", new int[] {1}))),
+            new Map[] {Map.of("Hello", "value")});
+    var json = adapter.toJson(instance);
+    var deserialized = adapter.fromJson(json);
+    assertThat(deserialized).isEqualTo(instance);
+  }
+
+  public static record SmokeTestType(
+      @Json(name = "first_name") String firstName,
+      @Json(name = "last_name") String lastName,
+      int age,
+      List<String> nationalities,
+      float weight,
+      Boolean tattoos, // Boxed primitive test
+      boolean hasChildren,
+      List<? super CharSequence> superWildcard,
+      List<? extends CharSequence> extendsWildcard,
+      List<?> unboundedWildcard,
+      List<Object> objectList,
+      int[] favoriteThreeNumbers,
+      String[] favoriteArrayValues,
+      Map<String, String> foodPreferences,
+      Set<List<Map<String, int[]>>> setListMapArrayInt,
+      Map<String, Object>[] nestedArray) {
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) return true;
+      if (o == null || getClass() != o.getClass()) return false;
+      SmokeTestType that = (SmokeTestType) o;
+      return age == that.age
+          && Float.compare(that.weight, weight) == 0
+          && hasChildren == that.hasChildren
+          && firstName.equals(that.firstName)
+          && lastName.equals(that.lastName)
+          && nationalities.equals(that.nationalities)
+          && Objects.equals(tattoos, that.tattoos)
+          && superWildcard.equals(that.superWildcard)
+          && extendsWildcard.equals(that.extendsWildcard)
+          && unboundedWildcard.equals(that.unboundedWildcard)
+          && objectList.equals(that.objectList)
+          && Arrays.equals(favoriteThreeNumbers, that.favoriteThreeNumbers)
+          && Arrays.equals(favoriteArrayValues, that.favoriteArrayValues)
+          && foodPreferences.equals(that.foodPreferences)
+          // && setListMapArrayInt.equals(that.setListMapArrayInt) // Nested array equality doesn't
+          // carry over
+          && Arrays.equals(nestedArray, that.nestedArray);
+    }
+
+    @Override
+    public int hashCode() {
+      int result =
+          Objects.hash(
+              firstName,
+              lastName,
+              age,
+              nationalities,
+              weight,
+              tattoos,
+              hasChildren,
+              superWildcard,
+              extendsWildcard,
+              unboundedWildcard,
+              objectList,
+              foodPreferences,
+              setListMapArrayInt);
+      result = 31 * result + Arrays.hashCode(favoriteThreeNumbers);
+      result = 31 * result + Arrays.hashCode(favoriteArrayValues);
+      result = 31 * result + Arrays.hashCode(nestedArray);
+      return result;
+    }
+  }
+
+  @Test
+  public void genericRecord() throws IOException {
+    var adapter =
+        moshi.<GenericRecord<String>>adapter(
+            Types.newParameterizedTypeWithOwner(
+                RecordsTest.class, GenericRecord.class, String.class));
+    assertThat(adapter.fromJson("{\"value\":\"Okay!\"}")).isEqualTo(new GenericRecord<>("Okay!"));
+  }
+
+  public static record GenericRecord<T>(T value) {}
+
+  @Test
+  public void genericBoundedRecord() throws IOException {
+    var adapter =
+        moshi.<GenericBoundedRecord<Integer>>adapter(
+            Types.newParameterizedTypeWithOwner(
+                RecordsTest.class, GenericBoundedRecord.class, Integer.class));
+    assertThat(adapter.fromJson("{\"value\":4}")).isEqualTo(new GenericBoundedRecord<>(4));
+  }
+
+  @Test
+  public void qualifiedValues() throws IOException {
+    var adapter = moshi.newBuilder().add(new ColorAdapter()).build().adapter(QualifiedValues.class);
+    assertThat(adapter.fromJson("{\"value\":\"#ff0000\"}"))
+        .isEqualTo(new QualifiedValues(16711680));
+  }
+
+  public static record QualifiedValues(@HexColor int value) {}
+
+  @Retention(RUNTIME)
+  @JsonQualifier
+  @interface HexColor {}
+
+  /** Converts strings like #ff0000 to the corresponding color ints. */
+  public static class ColorAdapter {
+    @ToJson
+    public String toJson(@HexColor int rgb) {
+      return String.format("#%06x", rgb);
+    }
+
+    @FromJson
+    @HexColor
+    public int fromJson(String rgb) {
+      return Integer.parseInt(rgb.substring(1), 16);
+    }
+  }
+
+  public static record GenericBoundedRecord<T extends Number>(T value) {}
+
+  @Test
+  public void jsonName() throws IOException {
+    var adapter = moshi.adapter(JsonName.class);
+    assertThat(adapter.fromJson("{\"actualValue\":3}")).isEqualTo(new JsonName(3));
+  }
+
+  public static record JsonName(@Json(name = "actualValue") int value) {}
+}

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

@@ -51,6 +51,7 @@ public final class Moshi {
     BUILT_IN_FACTORIES.add(CollectionJsonAdapter.FACTORY);
     BUILT_IN_FACTORIES.add(MapJsonAdapter.FACTORY);
     BUILT_IN_FACTORIES.add(ArrayJsonAdapter.FACTORY);
+    BUILT_IN_FACTORIES.add(RecordJsonAdapter.FACTORY);
     BUILT_IN_FACTORIES.add(ClassJsonAdapter.FACTORY);
   }
 

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

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2021 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
+ *
+ *    https://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;
+
+import java.io.IOException;
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.util.Set;
+import javax.annotation.Nullable;
+
+/**
+ * This is just a simple shim for linking in {@link StandardJsonAdapters} and swapped with a real
+ * implementation in Java 16 via MR Jar.
+ */
+final class RecordJsonAdapter<T> extends JsonAdapter<T> {
+
+  static final JsonAdapter.Factory FACTORY =
+      new JsonAdapter.Factory() {
+
+        @Nullable
+        @Override
+        public JsonAdapter<?> create(
+            Type type, Set<? extends Annotation> annotations, Moshi moshi) {
+          return null;
+        }
+      };
+
+  @Nullable
+  @Override
+  public T fromJson(JsonReader reader) throws IOException {
+    throw new AssertionError();
+  }
+
+  @Override
+  public void toJson(JsonWriter writer, @Nullable T value) throws IOException {
+    throw new AssertionError();
+  }
+}

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

@@ -0,0 +1,218 @@
+/*
+ * Copyright (C) 2021 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
+ *
+ *    https://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;
+
+import static java.lang.invoke.MethodType.methodType;
+
+import java.io.IOException;
+import java.lang.annotation.Annotation;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.RecordComponent;
+import java.lang.reflect.Type;
+import java.lang.reflect.TypeVariable;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * A {@link JsonAdapter} that supports Java {@code record} classes via reflection.
+ *
+ * <p><em>NOTE:</em> Java records require JDK 16 or higher.
+ */
+final class RecordJsonAdapter<T> extends JsonAdapter<T> {
+
+  static final JsonAdapter.Factory FACTORY =
+      (type, annotations, moshi) -> {
+        if (!annotations.isEmpty()) {
+          return null;
+        }
+
+        if (!(type instanceof Class) && !(type instanceof ParameterizedType)) {
+          return null;
+        }
+
+        var rawType = Types.getRawType(type);
+        if (!rawType.isRecord()) {
+          return null;
+        }
+
+        Map<String, Type> mappedTypeArgs = null;
+        if (type instanceof ParameterizedType parameterizedType) {
+          Type[] typeArgs = parameterizedType.getActualTypeArguments();
+          var typeVars = rawType.getTypeParameters();
+          mappedTypeArgs = new LinkedHashMap<>(typeArgs.length);
+          for (int i = 0; i < typeArgs.length; ++i) {
+            var typeVarName = typeVars[i].getName();
+            var materialized = typeArgs[i];
+            mappedTypeArgs.put(typeVarName, materialized);
+          }
+        }
+        var components = rawType.getRecordComponents();
+        var bindings = new LinkedHashMap<String, ComponentBinding<?>>();
+        var constructorParams = new Class<?>[components.length];
+        var lookup = MethodHandles.lookup();
+        for (int i = 0, componentsLength = components.length; i < componentsLength; i++) {
+          RecordComponent component = components[i];
+          constructorParams[i] = component.getType();
+          var name = component.getName();
+          var componentType = component.getGenericType();
+          if (componentType instanceof TypeVariable<?> typeVariable) {
+            var typeVarName = typeVariable.getName();
+            if (mappedTypeArgs == null) {
+              throw new AssertionError(
+                  "No mapped type arguments found for type '" + typeVarName + "'");
+            }
+            var mappedType = mappedTypeArgs.get(typeVarName);
+            if (mappedType == null) {
+              throw new AssertionError(
+                  "No materialized type argument found for type '" + typeVarName + "'");
+            }
+            componentType = mappedType;
+          }
+          var jsonName = name;
+          Set<Annotation> qualifiers = null;
+          for (var annotation : component.getDeclaredAnnotations()) {
+            if (annotation instanceof Json jsonAnnotation) {
+              jsonName = jsonAnnotation.name();
+            } else {
+              if (annotation.annotationType().isAnnotationPresent(JsonQualifier.class)) {
+                if (qualifiers == null) {
+                  qualifiers = new LinkedHashSet<>();
+                }
+                qualifiers.add(annotation);
+              }
+            }
+          }
+          if (qualifiers == null) {
+            qualifiers = Collections.emptySet();
+          }
+          var adapter = moshi.adapter(componentType, qualifiers);
+          MethodHandle accessor;
+          try {
+            accessor = lookup.unreflect(component.getAccessor());
+          } catch (IllegalAccessException e) {
+            throw new AssertionError(e);
+          }
+          var componentBinding = new ComponentBinding<>(name, jsonName, adapter, accessor);
+          var replaced = bindings.put(jsonName, componentBinding);
+          if (replaced != null) {
+            throw new IllegalArgumentException(
+                "Conflicting components:\n"
+                    + "    "
+                    + replaced.name
+                    + "\n"
+                    + "    "
+                    + componentBinding.name);
+          }
+        }
+
+        MethodHandle constructor;
+        try {
+          constructor = lookup.findConstructor(rawType, methodType(void.class, constructorParams));
+        } catch (NoSuchMethodException | IllegalAccessException e) {
+          throw new AssertionError(e);
+        }
+        return new RecordJsonAdapter<>(constructor, rawType.getSimpleName(), bindings).nullSafe();
+      };
+
+  private static record ComponentBinding<T>(
+      String name, String jsonName, JsonAdapter<T> adapter, MethodHandle accessor) {}
+
+  private final String targetClass;
+  private final MethodHandle constructor;
+  private final ComponentBinding<Object>[] componentBindingsArray;
+  private final JsonReader.Options options;
+
+  @SuppressWarnings("ToArrayCallWithZeroLengthArrayArgument")
+  public RecordJsonAdapter(
+      MethodHandle constructor,
+      String targetClass,
+      Map<String, ComponentBinding<?>> componentBindings) {
+    this.constructor = constructor;
+    this.targetClass = targetClass;
+    //noinspection unchecked
+    this.componentBindingsArray =
+        componentBindings.values().toArray(new ComponentBinding[componentBindings.size()]);
+    this.options =
+        JsonReader.Options.of(
+            componentBindings.keySet().toArray(new String[componentBindings.size()]));
+  }
+
+  @Override
+  public T fromJson(JsonReader reader) throws IOException {
+    var resultsArray = new Object[componentBindingsArray.length];
+
+    reader.beginObject();
+    while (reader.hasNext()) {
+      int index = reader.selectName(options);
+      if (index == -1) {
+        reader.skipName();
+        reader.skipValue();
+        continue;
+      }
+      var result = componentBindingsArray[index].adapter.fromJson(reader);
+      resultsArray[index] = result;
+    }
+    reader.endObject();
+
+    try {
+      //noinspection unchecked
+      return (T) constructor.invokeWithArguments(resultsArray);
+    } catch (Throwable e) {
+      if (e instanceof InvocationTargetException ite) {
+        Throwable cause = ite.getCause();
+        if (cause instanceof RuntimeException) throw (RuntimeException) cause;
+        if (cause instanceof Error) throw (Error) cause;
+        throw new RuntimeException(cause);
+      } else {
+        throw new AssertionError(e);
+      }
+    }
+  }
+
+  @Override
+  public void toJson(JsonWriter writer, T value) throws IOException {
+    writer.beginObject();
+
+    for (var binding : componentBindingsArray) {
+      writer.name(binding.jsonName);
+      try {
+        binding.adapter.toJson(writer, binding.accessor.invoke(value));
+      } catch (Throwable e) {
+        if (e instanceof InvocationTargetException ite) {
+          Throwable cause = ite.getCause();
+          if (cause instanceof RuntimeException) throw (RuntimeException) cause;
+          if (cause instanceof Error) throw (Error) cause;
+          throw new RuntimeException(cause);
+        } else {
+          throw new AssertionError(e);
+        }
+      }
+    }
+
+    writer.endObject();
+  }
+
+  @Override
+  public String toString() {
+    return "JsonAdapter(" + targetClass + ")";
+  }
+}

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

@@ -126,7 +126,7 @@ public final class JsonAdapterTest {
       fail();
     } catch (JsonDataException expected) {
       assertThat(expected).hasMessageThat().isEqualTo("Unexpected null at $[1]");
-      assertThat(reader.nextNull()).isNull();
+      assertThat(reader.<Object>nextNull()).isNull();
     }
     assertThat(toUpperCase.fromJson(reader)).isEqualTo("C");
     reader.endArray();

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

@@ -565,7 +565,7 @@ public final class JsonReaderTest {
     assertThat(reader2.peek()).isEqualTo(JsonReader.Token.END_DOCUMENT);
 
     JsonReader reader3 = newReader("null");
-    assertThat(reader3.nextNull()).isNull();
+    assertThat(reader3.<Object>nextNull()).isNull();
     assertThat(reader3.peek()).isEqualTo(JsonReader.Token.END_DOCUMENT);
 
     JsonReader reader4 = newReader("123");

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

@@ -59,7 +59,7 @@ public final class JsonValueReaderTest {
 
     assertThat(reader.hasNext()).isTrue();
     assertThat(reader.peek()).isEqualTo(JsonReader.Token.NULL);
-    assertThat(reader.nextNull()).isNull();
+    assertThat(reader.<Object>nextNull()).isNull();
 
     assertThat(reader.hasNext()).isFalse();
     assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_ARRAY);
@@ -103,7 +103,7 @@ public final class JsonValueReaderTest {
     assertThat(reader.peek()).isEqualTo(JsonReader.Token.NAME);
     assertThat(reader.nextName()).isEqualTo("d");
     assertThat(reader.peek()).isEqualTo(JsonReader.Token.NULL);
-    assertThat(reader.nextNull()).isNull();
+    assertThat(reader.<Object>nextNull()).isNull();
 
     assertThat(reader.hasNext()).isFalse();
     assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_OBJECT);

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

@@ -152,10 +152,10 @@ public final class JsonValueWriterTest {
   public void primitiveIntegerTypesEmitLong() throws Exception {
     JsonValueWriter writer = new JsonValueWriter();
     writer.beginArray();
-    writer.value(new Byte(Byte.MIN_VALUE));
-    writer.value(new Short(Short.MIN_VALUE));
-    writer.value(new Integer(Integer.MIN_VALUE));
-    writer.value(new Long(Long.MIN_VALUE));
+    writer.value(Byte.valueOf(Byte.MIN_VALUE));
+    writer.value(Short.valueOf(Short.MIN_VALUE));
+    writer.value(Integer.valueOf(Integer.MIN_VALUE));
+    writer.value(Long.valueOf(Long.MIN_VALUE));
     writer.endArray();
 
     List<Number> numbers =
@@ -167,8 +167,8 @@ public final class JsonValueWriterTest {
   public void primitiveFloatingPointTypesEmitDouble() throws Exception {
     JsonValueWriter writer = new JsonValueWriter();
     writer.beginArray();
-    writer.value(new Float(0.5f));
-    writer.value(new Double(0.5d));
+    writer.value(Float.valueOf(0.5f));
+    writer.value(Double.valueOf(0.5d));
     writer.endArray();
 
     List<Number> numbers = Arrays.<Number>asList(0.5d, 0.5d);

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

@@ -236,17 +236,17 @@ public final class JsonWriterTest {
     JsonWriter writer = factory.newWriter();
     writer.beginArray();
     try {
-      writer.value(new Double(Double.NaN));
+      writer.value(Double.valueOf(Double.NaN));
       fail();
     } catch (IllegalArgumentException expected) {
     }
     try {
-      writer.value(new Double(Double.NEGATIVE_INFINITY));
+      writer.value(Double.valueOf(Double.NEGATIVE_INFINITY));
       fail();
     } catch (IllegalArgumentException expected) {
     }
     try {
-      writer.value(new Double(Double.POSITIVE_INFINITY));
+      writer.value(Double.valueOf(Double.POSITIVE_INFINITY));
       fail();
     } catch (IllegalArgumentException expected) {
     }

settings.gradle.kts

@@ -24,6 +24,7 @@ pluginManagement {
 rootProject.name = "moshi-root"
 include(":moshi")
 include(":moshi:japicmp")
+include(":moshi:records-tests")
 include(":adapters")
 include(":adapters:japicmp")
 include(":examples")