False Negative: ContinueInFalseLoop.ql misses do ... while(false) loops once false is stored in a local.

Version
codeql 2.24.3

Checker

• Checker id: Likely Bugs/Statements/ContinueInFalseLoop.ql
• Checker description: This checker detects a 'continue' statement inside a 'do' loop whose condition is always false, meaning the continue will never actually re-run the loop body.

Description of the false negative

Both samples are still do loops whose condition is false and therefore cannot loop back after continue. The only difference is that the literal false is first assigned to a local variable.

That should still be a direct hit for Likely Bugs/Statements/ContinueInFalseLoop.ql.

Affected test cases

PosCase1_Var1.java

never is a constant false value, so the continue still cannot re-enter the loop body.

// A do loop with a literal false condition contains a continue statement targeting that same loop should be flagged as a positive case.
package scensct.var.pos;

public class PosCase1_Var1 {
    public static void main(String[] args) {
        final boolean never = false;
        do {
            // continue inside do with false condition
            continue;
        } while (never);
    }
}

PosCase1_Var5.java

flag is initialized from Boolean.FALSE and never changed. This is still the same impossible loop-back case.

// A do loop with a literal false condition contains a continue statement targeting that same loop should be flagged as a positive case.
package scensct.var.pos;

public class PosCase1_Var5 {
    public static void main(String[] args) {
        boolean flag = Boolean.FALSE;
        do {
            // continue inside do with false condition
            continue;
        } while (flag);
    }
}

Cause analysis

The miss is surprisingly basic. The query appears to require a literal false at the loop condition and loses the result as soon as that same value is stored in a local.

For developers, these are the same bug. Whether the condition is written as while (false) or while (never) should not matter.

References

None known.