static @NotNull String childUrl(@NotNull String parentUrl, @NotNull CharSequence childName, @NotNull NewVirtualFileSystem fs) {
    if (childName.equals(JarFileSystem.JAR_SEPARATOR) && fs instanceof ArchiveFileSystem) {
      return VirtualFileManager.constructUrl(fs.getProtocol(), StringUtil.trimEnd(VfsUtilCore.urlToPath(parentUrl), '/')) + childName;
    }
    return parentUrl.isEmpty() ? VirtualFileManager.constructUrl(fs.getProtocol(), childName.toString()) :
           VirtualFileManager.constructUrl(fs.getProtocol(), StringUtil.trimEnd(VfsUtilCore.urlToPath(parentUrl), '/')) + '/' + childName;
  }
static @NotNull String childUrl(@NotNull String parentUrl, @NotNull CharSequence childName, @NotNull NewVirtualFileSystem fs)