Condition is always True or always False

ID

vbnet.correctness.condition_always_true

Severity

high

Remediation Complexity

medium

Remediation Risk

medium

Remediation Effort

low

Resource

Control Flow

Language

VB.NET

Description

Flags an If or ElseIf whose condition is a constant written in the source: the literal forms If True Then and If False Then, and expressions that fold to a literal such as If Not False Then. Only a literal condition is reported. A condition on a variable is never reported, even when the variable is assigned a constant a few lines earlier and never reassigned, because deciding that safely needs flow analysis this rule deliberately does not do — a flag can be reassigned in a nested block, in a Catch, or through a ByRef argument without the assignment being visible at the test. While True loops are also left alone: an unconditional loop is an idiom, not a mistaken condition.

Rationale

A condition with a fixed outcome means one side of the branch can never run: an always-True test makes the Else dead, an always-False test makes the body dead. The code still reads as though a decision were being made, so a reviewer credits the program with behaviour it does not have — the fallback path is never exercised, the feature is permanently on or permanently off. Debug switches and feature flags hard-wired during development are the common source, and they survive precisely because nothing fails: the program keeps working while one entire path goes untaken, often for the whole life of the release.

The following code illustrates the pattern detected by this rule:

Public Sub Publish(ByVal draft As Boolean)
    ' FLAGGED: Condition is always True or always False
    If True Then
        Save()
    Else
        Discard()
    End If
End Sub

Remediation

Restore the condition that was meant to be tested, or remove the test together with the branch that can never run.

' Before: a hard-wired literal makes the Else unreachable
Public Sub Export()
    If True Then
        CompressAndWrite()
    Else
        Write()
    End If
End Sub

' After: the decision belongs to the caller
Public Sub Export(ByVal useCompression As Boolean)
    If useCompression Then
        CompressAndWrite()
    Else
        Write()
    End If
End Sub

Configuration

This detector does not need any configuration.

References