1 files changed, 49 insertions, 8 deletions
diff --git a/java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java b/java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java
index 65cf7385..5e4d7739 100644
--- a/java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java
+++ b/java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java
@@ -79,6 +79,22 @@ public class ExtensionRegistryLite {
   // applications. Need to support this feature on smaller granularity.
   private static volatile boolean eagerlyParseMessageSets = false;
 
+  // Visible for testing.
+  static final String EXTENSION_CLASS_NAME = "com.google.protobuf.Extension";
+
+  /* @Nullable */
+  static Class<?> resolveExtensionClass() {
+    try {
+      return Class.forName(EXTENSION_CLASS_NAME);
+    } catch (ClassNotFoundException e) {
+      // See comment in ExtensionRegistryFactory on the potential expense of this.
+      return null;
+    }
+  }
+
+  /* @Nullable */
+  private static final Class<?> extensionClass = resolveExtensionClass();
+
   public static boolean isEagerlyParseMessageSets() {
     return eagerlyParseMessageSets;
   }
@@ -87,14 +103,22 @@ public class ExtensionRegistryLite {
     eagerlyParseMessageSets = isEagerlyParse;
   }
 
-  /** Construct a new, empty instance. */
+  /**
+   * Construct a new, empty instance.
+   * 
+   * <p>
+   * This may be an {@code ExtensionRegistry} if the full (non-Lite) proto libraries are available.
+   */
   public static ExtensionRegistryLite newInstance() {
-    return new ExtensionRegistryLite();
+    return ExtensionRegistryFactory.create();
   }
 
-  /** Get the unmodifiable singleton empty instance. */
+  /**
+   * Get the unmodifiable singleton empty instance of either ExtensionRegistryLite or
+   * {@code ExtensionRegistry} (if the full (non-Lite) proto libraries are available).
+   */
   public static ExtensionRegistryLite getEmptyRegistry() {
-    return EMPTY;
+    return ExtensionRegistryFactory.createEmpty();
   }
 
   /** Returns an unmodifiable view of the registry. */
@@ -128,6 +152,23 @@ public class ExtensionRegistryLite {
       extension);
   }
 
+  /**
+   * Add an extension from a lite generated file to the registry only if it is
+   * a non-lite extension i.e. {@link GeneratedMessageLite.GeneratedExtension}. */
+  public final void add(ExtensionLite<?, ?> extension) {
+    if (GeneratedMessageLite.GeneratedExtension.class.isAssignableFrom(extension.getClass())) {
+      add((GeneratedMessageLite.GeneratedExtension<?, ?>) extension);
+    }
+    if (ExtensionRegistryFactory.isFullRegistry(this)) {
+      try {
+        this.getClass().getMethod("add", extensionClass).invoke(this, extension);
+      } catch (Exception e) {
+        throw new IllegalArgumentException(
+            String.format("Could not invoke ExtensionRegistry#add for %s", extension), e);
+      }
+    }
+  }
+
   // =================================================================
   // Private stuff.
 
@@ -139,9 +180,11 @@ public class ExtensionRegistryLite {
         new HashMap<ObjectIntPair,
                     GeneratedMessageLite.GeneratedExtension<?, ?>>();
   }
+  static final ExtensionRegistryLite EMPTY_REGISTRY_LITE =
+      new ExtensionRegistryLite(true);
 
   ExtensionRegistryLite(ExtensionRegistryLite other) {
-    if (other == EMPTY) {
+    if (other == EMPTY_REGISTRY_LITE) {
       this.extensionsByNumber = Collections.emptyMap();
     } else {
       this.extensionsByNumber =
@@ -153,11 +196,9 @@ public class ExtensionRegistryLite {
                     GeneratedMessageLite.GeneratedExtension<?, ?>>
       extensionsByNumber;
 
-  private ExtensionRegistryLite(boolean empty) {
+  ExtensionRegistryLite(boolean empty) {
     this.extensionsByNumber = Collections.emptyMap();
   }
-  private static final ExtensionRegistryLite EMPTY =
-    new ExtensionRegistryLite(true);
 
   /** A (Object, int) pair, used as a map key. */
   private static final class ObjectIntPair {