Make @AutoAnnotation instances serializable.

RELNOTES=`@AutoAnnotation` instances are now serializable.
PiperOrigin-RevId: 331666372

Author: eamonnmcmanus

value/src/it/functional/src/test/java/com/google/auto/value/AutoAnnotationTest.java

@@ -26,6 +26,7 @@
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.primitives.Ints;
 import com.google.common.testing.EqualsTester;
+import com.google.common.testing.SerializableTester;
 import java.lang.annotation.Annotation;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -406,6 +407,14 @@ public void testEqualsAndHashCode() {
         .testEquals();
   }
 
+  @Test
+  public void testSerialization() {
+    Annotation[] instances = {EVERYTHING_FROM_AUTO, EVERYTHING_FROM_AUTO_COLLECTIONS};
+    for (Annotation instance : instances) {
+      SerializableTester.reserializeAndAssert(instance);
+    }
+  }
+
   public static class IntList extends ArrayList<Integer> {
     IntList(Collection<Integer> c) {
       super(c);

value/src/main/java/com/google/auto/value/processor/autoannotation.vm

@@ -45,7 +45,8 @@ package $pkg;
 #else
 // Generated by com.google.auto.value.processor.AutoAnnotationProcessor
 #end
-final class $className implements $annotationName {
+final class $className implements $annotationName, `java.io.Serializable` {
+  private static final long serialVersionUID = 1L;
 
 ## Fields
 

value/src/test/java/com/google/auto/value/processor/AutoAnnotationCompilationTest.java

@@ -74,11 +74,13 @@ public void testSimple() {
             "",
             "import com.example.annotations.MyAnnotation;",
             "import com.example.enums.MyEnum;",
+            "import java.io.Serializable;",
             GeneratedImport.importGeneratedAnnotationType(),
             "",
             "@Generated(\"" + AutoAnnotationProcessor.class.getName() + "\")",
             "final class AutoAnnotation_AnnotationFactory_newMyAnnotation",
-            "     implements MyAnnotation {",
+            "     implements MyAnnotation, Serializable {",
+            "  private static final long serialVersionUID = 1L;",
             "  private final MyEnum value;",
             "  private static final int defaultedValue = 23;",
             "",
@@ -157,11 +159,13 @@ public void testEmptyPackage() {
     JavaFileObject expectedOutput =
         JavaFileObjects.forSourceLines(
             "AutoAnnotation_AnnotationFactory_newMyAnnotation",
+            "import java.io.Serializable;",
             GeneratedImport.importGeneratedAnnotationType(),
             "",
             "@Generated(\"" + AutoAnnotationProcessor.class.getName() + "\")",
             "final class AutoAnnotation_AnnotationFactory_newMyAnnotation",
-            "    implements MyAnnotation {",
+            "    implements MyAnnotation, Serializable {",
+            "  private static final long serialVersionUID = 1L;",
             "  AutoAnnotation_AnnotationFactory_newMyAnnotation() {",
             "  }",
             "",
@@ -237,12 +241,14 @@ public void testGwtSimple() {
             "package com.example.factories;",
             "",
             "import com.example.annotations.MyAnnotation;",
+            "import java.io.Serializable",
             "import java.util.Arrays;",
             GeneratedImport.importGeneratedAnnotationType(),
             "",
             "@Generated(\"" + AutoAnnotationProcessor.class.getName() + "\")",
-            "final class AutoAnnotation_AnnotationFactory_newMyAnnotation implements MyAnnotation"
-                + " {",
+            "final class AutoAnnotation_AnnotationFactory_newMyAnnotation implements MyAnnotation,"
+                + " Serializable {",
+            "  private static final long serialVersionUID = 1L;",
             "  private final int[] value;",
             "",
             "  AutoAnnotation_AnnotationFactory_newMyAnnotation(int[] value) {",
@@ -343,15 +349,17 @@ public void testCollectionsForArrays() {
             "",
             "import com.example.annotations.MyAnnotation;",
             "import com.example.enums.MyEnum;",
+            "import java.io.Serializable;",
             "import java.util.Arrays;",
             "import java.util.Collection;",
             "import java.util.List;",
             "import java.util.Set;",
             GeneratedImport.importGeneratedAnnotationType(),
             "",
             "@Generated(\"" + AutoAnnotationProcessor.class.getName() + "\")",
-            "final class AutoAnnotation_AnnotationFactory_newMyAnnotation implements MyAnnotation"
-                + " {",
+            "final class AutoAnnotation_AnnotationFactory_newMyAnnotation implements MyAnnotation,"
+                + " Serializable {",
+            "  private static final long serialVersionUID = 1L;",
             "  private final int[] value;",
             "  private final MyEnum[] enums;",
             "",