Change RubyBasicObject.to_a to IRubyObject return

.diff

diff --git a/core/src/main/java/org/jruby/RubyBasicObject.java b/core/src/main/java/org/jruby/RubyBasicObject.java
index 5ec44d5129..c0e5121211 100644
--- a/core/src/main/java/org/jruby/RubyBasicObject.java
+++ b/core/src/main/java/org/jruby/RubyBasicObject.java
@@ -2571,7 +2571,7 @@ public class RubyBasicObject implements Cloneable, IRubyObject, Serializable, Co
      *
      *  The default to_a method is deprecated.
      */
-    public RubyArray to_a(ThreadContext context) {
+    public IRubyObject to_a(ThreadContext context) {
         Ruby runtime = context.runtime;
         runtime.getWarnings().warn(ID.DEPRECATED_METHOD, "default 'to_a' will be obsolete");
         return runtime.newArray(this);
@@ -3228,7 +3228,7 @@ public class RubyBasicObject implements Cloneable, IRubyObject, Serializable, Co
 
     @Deprecated
     public RubyArray to_a() {
-        return to_a(getRuntime().getCurrentContext());
+        return to_a(getRuntime().getCurrentContext()).convertToArray();
     }
 
     @Deprecated
diff --git a/core/src/main/java/org/jruby/RubyHash.java b/core/src/main/java/org/jruby/RubyHash.java
index d6658775be..3ee861358c 100644
--- a/core/src/main/java/org/jruby/RubyHash.java
+++ b/core/src/main/java/org/jruby/RubyHash.java
@@ -916,7 +916,7 @@ public class RubyHash extends RubyObject implements Map {
      */
     @JRubyMethod(name = "to_a")
     @Override
-    public RubyArray to_a(ThreadContext context) {
+    public IRubyObject to_a(ThreadContext context) {
         final Ruby runtime = context.runtime;
         try {
             final RubyArray result = RubyArray.newBlankArrayInternal(runtime, size);
@@ -1582,7 +1582,7 @@ public class RubyHash extends RubyObject implements Map {
 
     @Deprecated
     public IRubyObject sort(ThreadContext context, Block block) {
-        return to_a(context).sort_bang(context, block);
+        return to_a(context).convertToArray().sort_bang(context, block);
     }
 
     /** rb_hash_index
@@ -2046,14 +2046,14 @@ public class RubyHash extends RubyObject implements Map {
 
     @JRubyMethod
     public IRubyObject flatten(ThreadContext context) {
-        RubyArray ary = to_a(context);
+        RubyArray ary = to_a(context).convertToArray();
         sites(context).flatten_bang.call(context, ary, ary, RubyFixnum.one(context.runtime));
         return ary;
     }
 
     @JRubyMethod
     public IRubyObject flatten(ThreadContext context, IRubyObject level) {
-        RubyArray ary = to_a(context);
+        RubyArray ary = to_a(context).convertToArray();
         sites(context).flatten_bang.call(context, ary, ary, level);
         return ary;
     }
@@ -2754,7 +2754,7 @@ public class RubyHash extends RubyObject implements Map {
     @Deprecated
     @Override
     public RubyArray to_a() {
-        return to_a(getRuntime().getCurrentContext());
+        return to_a(getRuntime().getCurrentContext()).convertToArray();
     }
 
     @Deprecated
diff --git a/core/src/main/java/org/jruby/RubyMatchData.java b/core/src/main/java/org/jruby/RubyMatchData.java
index 00cf222c5c..1bd545a6a8 100644
--- a/core/src/main/java/org/jruby/RubyMatchData.java
+++ b/core/src/main/java/org/jruby/RubyMatchData.java
@@ -584,7 +584,7 @@ public class RubyMatchData extends RubyObject {
     public IRubyObject op_aref(ThreadContext context, IRubyObject idx) {
         check();
         IRubyObject result = op_arefCommon(idx);
-        return result == null ? to_a(context).aref(idx) : result;
+        return result == null ? to_a(context).convertToArray().aref(idx) : result;
     }
 
     /** match_aref
@@ -593,7 +593,7 @@ public class RubyMatchData extends RubyObject {
     @JRubyMethod(name = "[]")
     public IRubyObject op_aref(ThreadContext context, IRubyObject idx, IRubyObject rest) {
         IRubyObject result;
-        return !rest.isNil() || (result = op_arefCommon(idx)) == null ? to_a(context).aref(idx, rest) : result;
+        return !rest.isNil() || (result = op_arefCommon(idx)) == null ? to_a(context).convertToArray().aref(idx, rest) : result;
     }
 
     private IRubyObject op_arefCommon(IRubyObject idx) {
diff --git a/core/src/main/java/org/jruby/ext/set/RubySet.java b/core/src/main/java/org/jruby/ext/set/RubySet.java
index 0db99dcc7c..3195dc5f6a 100644
--- a/core/src/main/java/org/jruby/ext/set/RubySet.java
+++ b/core/src/main/java/org/jruby/ext/set/RubySet.java
@@ -695,7 +695,7 @@ public class RubySet extends RubyObject implements Set {
             return enumeratorizeWithSize(context, this, "collect!", enumSize());
         }
 
-        final RubyArray elems = to_a(context); clearImpl();
+        final RubyArray elems = to_a(context).convertToArray(); clearImpl();
         for ( int i=0; i<elems.size(); i++ ) {
             addImpl(context.runtime, block.yield(context, elems.eltInternal(i)));
         }
diff --git a/core/src/main/java/org/jruby/java/proxies/MapJavaProxy.java b/core/src/main/java/org/jruby/java/proxies/MapJavaProxy.java
index 9dad20d598..6d9162e27f 100644
--- a/core/src/main/java/org/jruby/java/proxies/MapJavaProxy.java
+++ b/core/src/main/java/org/jruby/java/proxies/MapJavaProxy.java
@@ -139,7 +139,7 @@ public final class MapJavaProxy extends ConcreteJavaProxy {
         @Override
         public RubyArray to_a(ThreadContext context) {
             syncSize();
-            return super.to_a(context);
+            return super.to_a(context).convertToArray();
         }
 
         @Override
@@ -468,7 +468,7 @@ public final class MapJavaProxy extends ConcreteJavaProxy {
     @Override
     @JRubyMethod(name = "to_a")
     public RubyArray to_a(ThreadContext context) {
-        return getOrCreateRubyHashMap(context.runtime).to_a(context);
+        return getOrCreateRubyHashMap(context.runtime).to_a(context).convertToArray();
     }
 
     @JRubyMethod(name = "to_proc")