@NotNull
  public static String buildStringToFindForIndicesFromRegExp(
      @NotNull String stringToFind, @NotNull Project project) {
    if (!Registry.is("idea.regexp.search.uses.indices")) return "";

    final AccessToken accessToken = ReadAction.start();
    try {
      final List<PsiElement> topLevelRegExpChars = getTopLevelRegExpChars("a", project);
      if (topLevelRegExpChars.size() != 1) return "";

      // leave only top level regExpChars
      return StringUtil.join(
          getTopLevelRegExpChars(stringToFind, project),
          new Function<PsiElement, String>() {
            final Class regExpCharPsiClass = topLevelRegExpChars.get(0).getClass();

            @Override
            public String fun(PsiElement element) {
              return regExpCharPsiClass.isInstance(element) ? element.getText() : " ";
            }
          },
          "");
    } finally {
      accessToken.finish();
    }
  }
  private static void logStats(Collection<PsiFile> otherFiles, long start) {
    long time = System.currentTimeMillis() - start;

    final Multiset<String> stats = HashMultiset.create();
    for (PsiFile file : otherFiles) {
      stats.add(
          StringUtil.notNullize(file.getViewProvider().getVirtualFile().getExtension())
              .toLowerCase());
    }

    List<String> extensions = ContainerUtil.newArrayList(stats.elementSet());
    Collections.sort(
        extensions,
        new Comparator<String>() {
          @Override
          public int compare(String o1, String o2) {
            return stats.count(o2) - stats.count(o1);
          }
        });

    String message =
        "Search in "
            + otherFiles.size()
            + " files with unknown types took "
            + time
            + "ms.\n"
            + "Mapping their extensions to an existing file type (e.g. Plain Text) might speed up the search.\n"
            + "Most frequent non-indexed file extensions: ";
    for (int i = 0; i < Math.min(10, extensions.size()); i++) {
      String extension = extensions.get(i);
      message += extension + "(" + stats.count(extension) + ") ";
    }
    LOG.info(message);
  }
 /** @deprecated to be removed in IDEA 16 */
 @Nullable
 public static Pattern createFileMaskRegExp(@Nullable String filter) {
   if (filter == null) {
     return null;
   }
   String pattern;
   final List<String> strings = StringUtil.split(filter, ",");
   if (strings.size() == 1) {
     pattern = PatternUtil.convertToRegex(filter.trim());
   } else {
     pattern =
         StringUtil.join(strings, s -> "(" + PatternUtil.convertToRegex(s.trim()) + ")", "|");
   }
   return Pattern.compile(pattern, Pattern.CASE_INSENSITIVE);
 }
 private static PsiElement[] getParameterElementsToSearch(final PsiParameter parameter) {
   final PsiMethod method = (PsiMethod) parameter.getDeclarationScope();
   PsiMethod[] overrides =
       OverridingMethodsSearch.search(method, true).toArray(PsiMethod.EMPTY_ARRAY);
   for (int i = 0; i < overrides.length; i++) {
     overrides[i] = (PsiMethod) overrides[i].getNavigationElement();
   }
   List<PsiElement> elementsToSearch = new ArrayList<PsiElement>(overrides.length + 1);
   elementsToSearch.add(parameter);
   int idx = method.getParameterList().getParameterIndex(parameter);
   for (PsiMethod override : overrides) {
     final PsiParameter[] parameters = override.getParameterList().getParameters();
     if (idx < parameters.length) {
       elementsToSearch.add(parameters[idx]);
     }
   }
   return elementsToSearch.toArray(new PsiElement[elementsToSearch.size()]);
 }
  private static List<PsiElement> getTopLevelRegExpChars(String regExpText, Project project) {
    @SuppressWarnings("deprecation")
    PsiFile file = PsiFileFactory.getInstance(project).createFileFromText("A.regexp", regExpText);
    List<PsiElement> result = null;
    final PsiElement[] children = file.getChildren();

    for (PsiElement child : children) {
      PsiElement[] grandChildren = child.getChildren();
      if (grandChildren.length != 1)
        return Collections
            .emptyList(); // a | b, more than one branch, can not predict in current way

      for (PsiElement grandGrandChild : grandChildren[0].getChildren()) {
        if (result == null) result = new ArrayList<>();
        result.add(grandGrandChild);
      }
    }
    return result != null ? result : Collections.<PsiElement>emptyList();
  }