Why is this an issue?

An operand of a boolean expression that never changes the result of the expression might not match the programmer’s intent and can lead to unexpected behavior and potential bugs.

var a = true;
if (a)
{
    DoSomething();
}

This also applies to the null coalescing operator when one of the operands always evaluates to null.

string d = null;
var v1 = d ?? "value";

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.

How to fix it

The conditions should be reviewed to decide whether:

• to update the unnecessary operand
• to remove the unnecessary operand

Code examples

Noncompliant code example

public void Sample(bool b, bool c)
{
    var a = true;
    if (a)                  // Noncompliant: "a" is always "true"
    {
        DoSomething();
    }

    if (b && a)             // Noncompliant: "a" is always "true"
    {
        DoSomething();
    }

    if (c || !a)            // Noncompliant: "!a" is always "false"
    {
        DoSomething();
    }

    string d = null;
    var v1 = d ?? "value";  // Noncompliant: "d" is always null and v1 is always "value".
    var v2 = s ?? d;        // Noncompliant: "d" is always null and v2 is always equal to s.
}

Compliant solution

The unnecessary operand is updated:

public void Sample(bool b, bool c, string s)
{
    var a = IsAllowed();
    if (a)                  // Compliant
    {
        DoSomething();
    }

    if (b && a)             // Compliant
    {
        DoSomething();
    }

    if (c || !a)            // Compliant
    {
        DoSomething();
    }

    string d = GetStringData();
    var v1 = d ?? "value";  // Compliant
    var v2 = s ?? d;        // Compliant
}

The unnecessary operand is removed:

public void Sample(bool b, bool c, string s)
{
    DoSomething();

    if (b)                  // Compliant
    {
        DoSomething();
    }

    if (c)                  // Compliant
    {
        DoSomething();
    }

    var v1 = "value";       // Compliant
    var v2 = s;             // Compliant
}

Resources

Documentation

• MITRE, CWE-571 - Expression is Always True
• MITRE, CWE-570 - Expression is Always False
• Conditional logical AND operator &&
• Conditional logical OR operator ||
• Null-coalescing operators ?? and ??=