Suppress field not initialized warning + improve readability

Author: horakivo

src/main/java/org/truffleruby/core/MarkingService.java

@@ -11,6 +11,7 @@
 
 import java.util.ArrayList;
 
+import org.truffleruby.annotations.SuppressFBWarnings;
 import org.truffleruby.cext.CapturedException;
 import org.truffleruby.cext.ValueWrapper;
 import org.truffleruby.core.array.ArrayUtils;
@@ -43,7 +44,7 @@ protected static final class ExtensionCallStackEntry {
 
         private final ExtensionCallStackEntry previous;
         ValueWrapper preservedObject;
-        ArrayList<ValueWrapper> preservedObjects;
+        @SuppressFBWarnings("UWF_FIELD_NOT_INITIALIZED_IN_CONSTRUCTOR") ArrayList<ValueWrapper> preservedObjectList;
         private final boolean keywordsGiven;
         private Object specialVariables;
         private final Object block;
@@ -79,7 +80,11 @@ public boolean hasKeptObjects() {
         }
 
         public boolean hasSingleKeptObject() {
-            return current.preservedObject != null && current.preservedObjects == null;
+            return current.preservedObject != null && current.preservedObjectList == null;
+        }
+
+        public boolean isPreservedObjectListInitialized() {
+            return current.preservedObjectList != null;
         }
 
         public void markOnExitObject(ValueWrapper value) {

src/main/java/org/truffleruby/core/MarkingServiceNodes.java

@@ -12,6 +12,7 @@
 import com.oracle.truffle.api.dsl.GenerateCached;
 import com.oracle.truffle.api.dsl.GenerateInline;
 import com.oracle.truffle.api.dsl.NeverDefault;
+import com.oracle.truffle.api.dsl.NonIdempotent;
 import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.profiles.InlinedConditionProfile;
 import org.truffleruby.cext.ValueWrapper;
@@ -52,20 +53,24 @@ static void keepCreatingList(Node node, ValueWrapper object,
             }
         }
 
-        @Specialization(guards = { "stack.hasKeptObjects()", "!stack.hasSingleKeptObject()" })
+        @Specialization(guards = {
+                "stack.isPreservedObjectListInitialized()",
+                "stack.hasKeptObjects()",
+                "!stack.hasSingleKeptObject()" })
         @TruffleBoundary
         static void keepAddingToList(Node node, ValueWrapper object,
                 @Bind("getStack(node)") ExtensionCallStack stack) {
-            stack.current.preservedObjects.add(object);
+            stack.current.preservedObjectList.add(object);
         }
 
         @TruffleBoundary
         private static void createKeptList(ValueWrapper object, ExtensionCallStack stack) {
-            stack.current.preservedObjects = new ArrayList<>();
-            stack.current.preservedObjects.add(stack.current.preservedObject);
-            stack.current.preservedObjects.add(object);
+            stack.current.preservedObjectList = new ArrayList<>();
+            stack.current.preservedObjectList.add(stack.current.preservedObject);
+            stack.current.preservedObjectList.add(object);
         }
 
+        @NonIdempotent
         protected static ExtensionCallStack getStack(Node node) {
             return getLanguage(node).getCurrentThread().getCurrentFiber().extensionCallStack;
         }