Conditional expressions which are always true or false can lead to dead code. Such code is always buggy and should never be used in production.

Noncompliant Code Example

public void Sample(bool b)
{
    bool a = false;
    if (a) // Noncompliant
    {
        DoSomething(); // never executed
    }

    if (!a || b) // Noncompliant; "!a" is always "true", "b" is never evaluated
    {
        DoSomething();
    }
    else
    {
        DoSomethingElse(); // never executed
    }

    var d = "xxx";
    var res = d ?? "value"; // Noncompliant, d is always not null, "value" is never used
}

Compliant Solution

public void Sample(bool b)
{
    bool a = false;
    if (Foo(a))
    {
        DoSomething();
    }

    if (b)
    {
        DoSomething();
    }
    else
    {
        DoSomethingElse();
    }

    var d = "xxx";
    var res = d;
}

Exceptions

This rule will not raise an issue in either of these cases:

• When the condition is a single const bool

const bool debug = false;
//...
if (debug)
{
  // Print something
}

• When the condition is the literal true or false.

In these cases it is obvious the code is as intended.

See

• MITRE, CWE-570 - Expression is Always False
• MITRE, CWE-571 - Expression is Always True