False Positive for Squid:3958 (Intermediate Stream methods should not be left unused)

[Paul Wagland]

Hi all,

As you have heard from me before, I love using SonarQube, and the additional rules that are being added only adds more value to an already valuable product!

We have been looking at Squid:3958, and have discovered a couple of false positive situations.

The first:

  public static void falsePositive1() {

    List<Boolean> list = new ArrayList<>();

    list.stream().filter(b -> !b.booleanValue()).sequential().collect(Collectors.toList());

    list.stream().filter(b -> !b.booleanValue()).collect(Collectors.toList());

  }

The underlined section is marked as unused intermediate stream methods. This is clearly nonsensical, as sequential() is called. Removing the call to sequential() causes the warning to go away. This can be seen in the second line, as there is no highlighting.

The second false positive:

  private static boolean a(Iterable<Boolean> iterable) { return true; }

  public static boolean falsePositive2() {

    List<Boolean> list = new ArrayList<>();

    Stream<Boolean> filter = StreamSupport.stream(list.spliterator(), false).filter(Boolean::booleanValue);

    return a(filter::iterator);

  }

Again, you can see the underlined section is where the warning is raised, however it is always used, as it is passed to a() as a lambda which uses the iterator(), and iterator() is a terminal operation. Note that calling the terminal operation directly is fine:

  public static boolean ok2() {

    List<Boolean> list = new ArrayList<>();

    Stream<Boolean> filter = StreamSupport.stream(list.spliterator(), false).filter(Boolean::booleanValue);

    filter.iterator();

    return true;

  }

It only seems to fail when passed as method reference to another method/class.

Cheers,

Paul

[Michael Gumowski]

Hey Paul,

Thanks for your feedback and precise, self-contained, reproducers. I created the following tickets to handle these cases independently: 

• SONARJAVA-2469 will handle BaseStream methods currently ignored
• SONARJAVA-2470 will handle method references consuming the stream
  

Cheers,

Michael

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Michael Gumowski | SonarSource

Software Developer, Language Team
http://sonarsource.com

[Paul Wagland]

On Tuesday, September 19, 2017 at 11:25:30 AM UTC+2, Michael Gumowski wrote:

Hey Paul,

Thanks for your feedback and precise, self-contained, reproducers. I created the following tickets to handle these cases independently: 

You are welcome, and, as always, thanks to you and your colleagues for a great product!

Cheers,

Paul