code: public boolean assist() {
          // Read the command line and provide assistance for the command line before the caret.
          final String commandLine = commandLineManager.getCommandLine();
          final int caret = commandLineManager.getCaret();
          final String commandLineToAssist = commandLine.substring(0, caret);
          final Opt<String> autoCompletedSuffix = shell.assist(commandLineToAssist);
          if (!autoCompletedSuffix.isPresent()) {
              return false;
          }
  
          // Don't overwrite any extra characters on the command line that came after the caret.
          final String extraCommandLine = commandLine.substring(caret);
          final String autoCompletedCommandLine = commandLineToAssist + autoCompletedSuffix.get();
          commandLineManager.setCommandLine(autoCompletedCommandLine + extraCommandLine);
          commandLineManager.setCaret(autoCompletedCommandLine.length());
          return true;
      }
docs: Provide assistance for the command line.
  
  @return {@code true} if assistance could be provided for the command line.