Two branches of a conditional have identical bodies

ID

vbnet.correctness.duplicate_branches

Severity

high

Remediation Complexity

medium

Remediation Risk

medium

Remediation Effort

low

Resource

Duplicate Logic

Language

VB.NET

Description

Flags a conditional whose two branches contain exactly the same statements: an If / Else pair with identical bodies of up to three statements, or two adjacent branches of an If / ElseIf chain with identical bodies of up to two statements. Longer bodies are not compared, and neither are duplicated branches separated by a branch that differs. Bodies that share only their first statement and then diverge are not reported.

Rationale

The condition that selects between the branches has no effect on what the program does, so either the code does not behave the way its shape suggests or it states the same thing twice. When one branch was meant to differ — the second amount, the other channel, a different template — the copy-paste left a real defect that is unusually hard to spot in review, because two symmetrical branches read as deliberate. When the branches genuinely are equivalent, the duplication is a maintenance liability instead: the next change has to be made in both places, and making it in only one reintroduces a difference nobody realised had been lost.

The following code illustrates the pattern detected by this rule:

Public Sub Notify(ByVal urgent As Boolean)
    ' FLAGGED: Two branches of a conditional have identical bodies
    If urgent Then
        SendEmail()
    Else
        SendEmail()
    End If
End Sub

Remediation

Fix the branch that was meant to differ. If the branches really are equivalent, drop the condition for an If/Else, or merge the two conditions with OrElse for an If/ElseIf chain.

' Before: both branches return the same value
If kind = 1 Then
    Return "email"
ElseIf kind = 2 Then
    Return "email"
End If

' After
If kind = 1 OrElse kind = 2 Then
    Return "email"
End If

Configuration

This detector does not need any configuration.

References