False positive for PSReviewUnusedParameter

[mlocati]

1. General summary of the issue

I have a function that declares a parameter. Even if it's is used in the function body, Pester says it's unused (PSReviewUnusedParameter warning).

2. Describe Your Environment

Pester version     : 4.10.1
PowerShell version : 5.1.17763.1007
OS version         : Windows Server 2019 Datacenter

3. Expected Behavior

Consider this code (extracted from a more complex file:

function Install-Php() {
    [OutputType()]
    param (
        [Parameter(Mandatory = $true, Position = 2, HelpMessage = 'Install a Thread-Safe version?')]
        [bool] $ThreadSafe
    )
    process {
        $searchReleaseStates = @()
        $versionToInstall = $null
        foreach ($searchReleaseState in $searchReleaseStates) {
            $compatibleVersions = Get-PhpAvailableVersion -State $searchReleaseState | Where-Object { $_.FullVersion -match '...' -and $_.Architecture -eq '...' -and $_.ThreadSafe -eq $ThreadSafe }
        }
    }
    end {
    }
}

Pester should not mark the $ThreadSafe parameter as unised.

4.Current Behavior

Pester raises a PSReviewUnusedParameter warning.

RuleName	Severity	ScriptName	Line	Message
PSReviewUnusedParameter	Warning	Install-Php.ps1	58	The parameter 'ThreadSafe' has been declared but not used.

(see here)

[nohwnd]

What you have there is a test written in Pester, but checking a PSScriptAnalyzer rule. I would not expect that rule to trigger either because you are using the variable on line 133.

@bergmeister is there anything that can be done differently? Or explicit exclusion is needed in some way?

RuleName                            Severity     ScriptName Line  Message                                              
--------                            --------     ---------- ----  -------                                              
PSReviewUnusedParameter             Warning      Install-Ph 58    The parameter 'ThreadSafe' has been declared but not 
                                                 p.ps1            used.                                                



    [-] D:\a\powershell-phpmanager\powershell-phpmanager\PhpManager\public\Install-Php.ps1 should pass PSScriptAnalyzer 185ms
      Expected 0, but got 1.
      21:             @($problems).Count | Should -Be 0
      at <ScriptBlock>, D:\a\powershell-phpmanager\powershell-phpmanager\test\tests\Syntax.Tests.ps1: line 21

[bergmeister]

This is a known PSSA issue as the new release added this new rule: PowerShell/PSScriptAnalyzer#1472

This is because the rule does not inspect child scriptblock scopes because depending on the command, the scope is not guaranteed to be passed on. In your case, Where-Object uses the same scope, so you can suppress the specific usage here but if it was Invoke-Command then PSSA would've been right. Because it doesn't know which command uses the same scope it made the decision to assume the scope is not used.

[mlocati]

What you have there is a test written in Pester, but checking a PSScriptAnalyzer rule

LOL, sorry! Long time passed since I wrote those tests, thanks for the heads-up btw, really appreciated!

[bergmeister]

@mlocati You're welcome. A parameter specific would be

function Install-Php() {
    [OutputType()]
    [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSReviewUnusedParameter', 'ThreadSafe',
        Justification = 'False positive as rule does not know that Where-Object operates within the same scope')]
    param (
        [Parameter(Mandatory = $true, Position = 2, HelpMessage = 'Install a Thread-Safe version?')]
        [bool] $ThreadSafe
    )
    process {
        $searchReleaseStates = @()
        $versionToInstall = $null
        foreach ($searchReleaseState in $searchReleaseStates) {
            $compatibleVersions = Get-PhpAvailableVersion -State $searchReleaseState | Where-Object { $_.FullVersion -match '...' -and $_.Architecture -eq '...' -and $_.ThreadSafe -eq $ThreadSafe }
        }
    }
    end {
    }
}

We are looking at making improvements in the next version to either white-list some known cmdlet that use the same scope or for the rule to be less strict by default (or both).

[mlocati]

Thank you again, @bergmeister, it worked out like a charm!

[MatthewMcD]

Adding this for folks landing here after migrating to Pester 5+ and PowerShell 7 like I just did. My tests began failing so I added the answer in this thread to the top of my test like this:

[Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSReviewUnusedParameter', 'Module',
        Justification = 'False positive as rule does not know that Module is used in the BeforeAll scope')]
Param (
    [String]$Module
)
BeforeAll{
    $functionName = (Get-Item $PSCommandPath ).BaseName.Replace(".Tests","")
    $ModuleData = Get-Module $Module
}