SystemConsoleNull should consider the case where System.console() == null

[anthonyvdotbe]

https://errorprone.info/bugpattern/SystemConsoleNull says:

System.console() no longer returns null in JDK 22 and newer versions

However, it may still return null, both from the specification and actual implementation.

So I propose to:

(a) rephrase the above sentence to

System.console() returns null in fewer cases in JDK 22 and newer versions

(b) update the code example to handle the case where System.console() == null:

  @SuppressWarnings("SystemConsoleNull") // https://errorprone.info/bugpattern/SystemConsoleNull
  private static boolean systemConsoleIsTerminal() {
    Console systemConsole = System.console();
    if (Runtime.version().feature() < 22) {
      return systemConsole != null;
    }
    try {
      return (systemConsole != null) && (Boolean) Console.class.getMethod("isTerminal").invoke(systemConsole);
    } catch (ReflectiveOperationException e) {
      throw new LinkageError(e.getMessage(), e);
    }
  }

[cushon]

Thanks, 'no longer returns null' could have been something like 'no longer returns null when the standard streams are redirected or connected to a virtual terminal'

Can the implementation return null, though? I'm not seeing how the implementation could return null in https://github.com/openjdk/jdk/blob/20cb6e786fbf6d924c509e28d6fded86d61a5f84/src/java.base/share/classes/java/io/Console.java#L431-L435

[anthonyvdotbe]

Can the implementation return null, though? I'm not seeing how the implementation could return null in https://github.com/openjdk/jdk/blob/20cb6e786fbf6d924c509e28d6fded86d61a5f84/src/java.base/share/classes/java/io/Console.java#L431-L435

At line 431, c can be null and istty can be false, which causes c to still be null at line 435. Or am I missing something?

[cpovirk]

Huh, thanks. I'd misread the code, too. Indeed, I can produce a null return:

$ cat SystemConsole.java
public class SystemConsole {
  public static void main(String[] args) {
    System.err.println(System.console());
  }
}

$ javac SystemConsole.java && ~/jdk-22-ea+19/bin/java -Djdk.console=nosuchthing SystemConsole > /dev/null
null

I'm hoping that that's at least possible only in the case that the user sets jdk.console (as above), but I wouldn't want to make further assumptions :)