Disallow `@AutoValue final class`.

We will otherwise try to generate a subclass for it which obviously won't compile. This is pretty unlikely anyway since a non-trivial `@AutoValue` class has to be abstract and a class can't be both final and abstract.

Fixes https://github.com/google/auto/issues/1215.

RELNOTES=n/a
PiperOrigin-RevId: 416042702

2 files changed, 32 insertions, 2 deletions

diff --git a/value/src/main/java/com/google/auto/value/processor/AutoValueishProcessor.java b/value/src/main/java/com/google/auto/value/processor/AutoValueishProcessor.java
index 56e8a98a..31f1ec1c 100644
--- a/value/src/main/java/com/google/auto/value/processor/AutoValueishProcessor.java
+++ b/value/src/main/java/com/google/auto/value/processor/AutoValueishProcessor.java
@@ -417,7 +417,7 @@ abstract class AutoValueishProcessor extends AbstractProcessor {
   /**
    * Validations common to all the subclasses. An {@code @AutoFoo} type must be a class, or possibly
    * an interface for {@code @AutoBuilder}. If it is a class then it must have a non-private no-arg
-   * constructor.
+   * constructor. And, since we'll be generating a subclass, it can't be final.
    */
   private void validateType(TypeElement type) {
     ElementKind kind = type.getKind();
@@ -441,6 +441,13 @@ abstract class AutoValueishProcessor extends AbstractProcessor {
           simpleAnnotationName,
           simpleAnnotationName);
     }
+    if (type.getModifiers().contains(Modifier.FINAL)) {
+      errorReporter.abortWithError(
+          type,
+          "[%sFinal] @%s class must not be final",
+          simpleAnnotationName,
+          simpleAnnotationName);
+    }
   }
 
   /**
diff --git a/value/src/test/java/com/google/auto/value/processor/AutoValueCompilationTest.java b/value/src/test/java/com/google/auto/value/processor/AutoValueCompilationTest.java
index cd21ef37..09d4faf9 100644
--- a/value/src/test/java/com/google/auto/value/processor/AutoValueCompilationTest.java
+++ b/value/src/test/java/com/google/auto/value/processor/AutoValueCompilationTest.java
@@ -577,6 +577,29 @@ public class AutoValueCompilationTest {
   }
 
   @Test
+  public void autoValueMustNotBeFinal() {
+    JavaFileObject javaFileObject =
+        JavaFileObjects.forSourceLines(
+            "foo.bar.Baz",
+            "package foo.bar;",
+            "",
+            "import com.google.auto.value.AutoValue;",
+            "",
+            "@AutoValue",
+            "public final class Baz {",
+            "  public Baz create() {",
+            "    return new AutoValue_Baz();",
+            "  }",
+            "}");
+    Compilation compilation =
+        javac().withProcessors(new AutoValueProcessor()).compile(javaFileObject);
+    assertThat(compilation)
+        .hadErrorContaining("@AutoValue class must not be final")
+        .inFile(javaFileObject)
+        .onLineContaining("class Baz");
+  }
+
+  @Test
   public void autoValueMustBeStatic() {
     JavaFileObject javaFileObject =
         JavaFileObjects.forSourceLines(
@@ -603,7 +626,7 @@ public class AutoValueCompilationTest {
   }
 
   @Test
-  public void autoValueMustBeNotBePrivate() {
+  public void autoValueMustNotBePrivate() {
     JavaFileObject javaFileObject =
         JavaFileObjects.forSourceLines(
             "foo.bar.Baz",