False positive with dereference.of.nullable

[mahfouz72]

The Checker Framework is flagging a possible null dereference in the below code snippet, where lambdaParameters.peek() is being checked for null before it is dereferenced. This seems to be a false positive, as the code should not cause a null dereference.

Code:

while (lambdaParameters.peek() != null
        && ast.equals(lambdaParameters.peek().enclosingLambda)) {

    final Optional<LambdaParameterDetails> unusedLambdaParameter =
            Optional.ofNullable(lambdaParameters.peek())
                    .filter(parameter -> !parameter.isUsed())
                    .filter(parameter -> !"_".equals(parameter.getName()));

    ....
}

---

Output:

New surviving error(s) found:

  <checkerFrameworkError unstable="false">
    <fileName>src/main/java/com/puppycrawl/tools/checkstyle/checks/coding/UnusedLambdaParameterShouldBeUnnamedCheck.java</fileName>
    <specifier>dereference.of.nullable</specifier>
    <message>dereference of possibly-null reference lambdaParameters.peek()</message>
    <lineContent>&amp;&amp; ast.equals(lambdaParameters.peek().enclosingLambda)) {</lineContent>
  </checkerFrameworkError>

---

Expectations:

This issue appears to be a false positive because lambdaParameters.peek() is explicitly checked for nullity before any dereferencing occurs. The error persists even though the code logic should prevent a null dereference.

---

Build tool: maven
checker version: 3.46.0

[smillst]

You've not given me enough of the code to reproduce this error. It could be that peek is not marked @SideEffectFree so lambdaParameters.peek() is unrefined.

[mahfouz72]

You can find the file here

peek() is a method in the Deque class from Java collections

[smillst]

Thanks! I can reproduce this:

package typearginfer;

import java.util.ArrayDeque;
import java.util.Deque;

public class Issue6760 {
  private final Deque<LambdaParameterDetails> lambdaParameters = new ArrayDeque<>();
  void method(DetailAST ast) {
    while (lambdaParameters.peek() != null
        && ast.equals(lambdaParameters.peek().enclosingLambda)) {
    }
  }
  static class LambdaParameterDetails {
    private  DetailAST enclosingLambda = new DetailAST();
  }
  static class DetailAST{}
}

Yes, It seems like peek needs to be marked sideeffect free in the annotated jdk.

[mernst]

Fixed by typetools/jdk#219.