@AutoCodec adds Singleton strategy.

PiperOrigin-RevId: 184889583

2 files changed, 31 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java
index a4f9fa7adb..be6a2bb47b 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java
@@ -67,6 +67,16 @@ public @interface AutoCodec {
      * uses its codec to serialize the data.
      */
     POLYMORPHIC,
+    /**
+     * For use with classes that are singleton.
+     *
+     * <p>Commonly used with the POLYMORPHIC strategy.
+     *
+     * <p>The serialized class must have a codec accessible, static INSTANCE field.
+     *
+     * <p>Illegal to use with a non-Void dependency.
+     */
+    SINGLETON
   }
 
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java
index f0fe3c0e1a..4d34175926 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java
@@ -110,6 +110,9 @@ public class AutoCodecProcessor extends AbstractProcessor {
         case POLYMORPHIC:
           codecClassBuilder = buildClassWithPolymorphicStrategy(encodedType, dependencyType);
           break;
+        case SINGLETON:
+          codecClassBuilder = buildClassWithSingletonStrategy(encodedType, dependencyType);
+          break;
         default:
           throw new IllegalArgumentException("Unknown strategy: " + annotation.strategy());
       }
@@ -607,6 +610,24 @@ public class AutoCodecProcessor extends AbstractProcessor {
     return builder.build();
   }
 
+  private static TypeSpec.Builder buildClassWithSingletonStrategy(
+      TypeElement encodedType, @Nullable TypeElement dependency) {
+    if (dependency != null) {
+      throw new IllegalArgumentException(
+          encodedType + " specifies a dependency, but SINGLETON is selected as the strategy.");
+    }
+    TypeSpec.Builder codecClassBuilder =
+        AutoCodecUtil.initializeCodecClassBuilder(encodedType, dependency);
+    // Serialization is a no-op.
+    codecClassBuilder.addMethod(
+        AutoCodecUtil.initializeSerializeMethodBuilder(encodedType, dependency).build());
+    MethodSpec.Builder deserializeMethodBuilder =
+        AutoCodecUtil.initializeDeserializeMethodBuilder(encodedType, dependency);
+    deserializeMethodBuilder.addStatement("return $T.INSTANCE", TypeName.get(encodedType.asType()));
+    codecClassBuilder.addMethod(deserializeMethodBuilder.build());
+    return codecClassBuilder;
+  }
+
   /** True when {@code type} has the same type as {@code clazz}. */
   private boolean matchesType(TypeMirror type, Class<?> clazz) {
     return env.getTypeUtils()