Implemented declared providers interface #1727

--
MOS_MIGRATED_REVID=133699895
diff --git a/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java b/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java
index 596675f..ec184b4 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java
@@ -26,11 +26,12 @@
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
 import com.google.devtools.build.lib.collect.nestedset.Order;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.events.Location;
 import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.syntax.ClassObject;
+import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.SkylarkNestedSet;
 import com.google.devtools.build.lib.util.Preconditions;
-
 import javax.annotation.Nullable;
 
 /**
@@ -75,6 +76,11 @@
   }
 
   @Override
+  public Object getIndex(Object key, Location loc) throws EvalException {
+    return actual == null ? null : actual.getIndex(key, loc);
+  }
+
+  @Override
   public Target getTarget() {
     return actual == null ? null : actual.getTarget();
   }