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Code Analyzer for C#

There is a newer version: 10.2.0.105762

Why is this an issue?
Conditional expressions which are always true or false can lead to unreachable code.
In the case below, the call of Dispose() never happens.
var a = false;
if (a)
{
    Dispose(); // Never reached
}

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 condition or 
   to remove the condition. 

Code examples
Noncompliant code example
public void Sample(bool b)
{
    bool a = false;
    if (a)                  // Noncompliant: The true branch is never reached
    {
        DoSomething();      // Never reached
    }

    if (!a || b)            // Noncompliant: "!a" is always "true" and the false branch is never reached
    {
        DoSomething();
    }
    else
    {
        DoSomethingElse();  // Never reached
    }

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

Compliant solution
public void Sample(bool b)
{
    bool a = false;
    if (Foo(a))             // Condition was updated
    {
        DoSomething();
    }

    if (b)                  // Parts of the condition were removed.
    {
        DoSomething();
    }
    else
    {
        DoSomethingElse();
    }

    var c = "xxx";
    var res = c;            // ?? "value" was removed
}

Resources

   CWE - CWE-570 - Expression is Always False 
   CWE - CWE-571 - Expression is Always True 
   Wikipedia - Unreachable code 

Documentation

   Microsoft Learn - Conditional logical AND operator && 
   Microsoft Learn - Conditional logical OR operator || 
   Microsoft Learn - ?? and ??=
  operators - the null-coalescing operators