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.

Dim a = False

If a Then
    Dispose() ' Never reached
End If

Exceptions

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

• When the condition is a single const bool

Const debug = False
'...
If debug Then
    ' Print something
End If

• 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 Sub Sample(ByVal b As Boolean)
    Dim a = False
    If a Then                   ' Noncompliant: The true branch is never reached
        DoSomething()           ' Never reached
    End If

    If Not a OrElse b Then      ' Noncompliant: "not a" is always "True" and the false branch is never reached
        DoSomething()
    Else
        DoSomethingElse()       ' Never reached
    End If

    Dim c = "xxx"
    Dim res = If(c, "value")    ' Noncompliant: d is always not Nothing, "value" is never used
End Sub

Compliant solution

Public Sub Sample(ByVal b As Boolean)
    Dim a = False
    If Foo(a) Then             ' Condition was updated
        DoSomething()
    End If

    If b Then                  ' Parts of the condition were removed.
        DoSomething()
    Else
        DoSomethingElse()
    End If

    Dim c = "xxx"
    Dim res = c                ' "value" was removed
End Sub

Resources

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

Documentation

• Microsoft Learn - Logical and Bitwise Operators in Visual Basic
• Microsoft Learn - ?. and ?() null-conditional operators (Visual Basic)
• Microsoft Learn - If operator called with two arguments