javac ast indices: remove redundant forceEnabled option from index writer

jps/jps-builders/src/org/jetbrains/jps/backwardRefs/BackwardReferenceIndexBuilder.java

@@ -42,11 +42,7 @@ public class BackwardReferenceIndexBuilder extends ModuleLevelBuilder {
 
   @Override
   public void buildFinished(CompileContext context) {
-    final BackwardReferenceIndexWriter writer = BackwardReferenceIndexWriter.getInstance();
-    if (writer != null) {
-      writer.close();
-    }
-    BackwardReferenceIndexWriter.clearInstance();
+    BackwardReferenceIndexWriter.closeIfNeed();
   }
 
   @Override

jps/jps-builders/src/org/jetbrains/jps/backwardRefs/BackwardReferenceIndexWriter.java

@@ -39,9 +39,7 @@ import java.util.*;
 import static com.sun.tools.javac.code.Flags.PRIVATE;
 
 public class BackwardReferenceIndexWriter {
-  public static final String PROP_KEY = "ref.index.builder";
-
-  public static volatile boolean forceEnabled;
+  public static final String PROP_KEY = "jps.backward.ref.index.builder";
 
   private static volatile BackwardReferenceIndexWriter ourInstance;
 
@@ -53,8 +51,14 @@ public class BackwardReferenceIndexWriter {
     myRebuild = rebuild;
   }
 
-  public static void clearInstance() {
-    ourInstance = null;
+  public static void closeIfNeed() {
+    if (ourInstance != null) {
+      try {
+        ourInstance.close();
+      } finally {
+        ourInstance = null;
+      }
+    }
   }
 
   static BackwardReferenceIndexWriter getInstance() {
@@ -85,7 +89,7 @@ public class BackwardReferenceIndexWriter {
   }
 
   public static boolean isEnabled() {
-    return SystemProperties.getBooleanProperty(PROP_KEY, false) || forceEnabled;
+    return SystemProperties.getBooleanProperty(PROP_KEY, false);
   }
 
   void close() {

jps/jps-builders/testSrc/org/jetbrains/references/ReferenceIndexTestBase.kt

@@ -31,16 +31,13 @@ import java.io.File
 
 abstract class ReferenceIndexTestBase : JpsBuildTestCase() {
   public override fun setUp() {
-    BackwardReferenceIndexWriter.forceEnabled = true
     super.setUp()
-//    System.setProperty(BackwardReferenceIndexWriter.PROP_KEY, true.toString())
+    System.setProperty(BackwardReferenceIndexWriter.PROP_KEY, true.toString())
   }
 
   public override fun tearDown() {
     super.tearDown()
-    BackwardReferenceIndexWriter.forceEnabled = false
-    BackwardReferenceIndexWriter.clearInstance()
-//    System.clearProperty(BackwardReferenceIndexWriter.PROP_KEY)
+    System.clearProperty(BackwardReferenceIndexWriter.PROP_KEY)
   }
 
   protected fun assertIndexOnRebuild(vararg files: String) {