Psscriptanalyzer: false variable is assigned but never used recommendation

[seajhawk]

Issue Type: Bug

I'm getting "The variable 'results' is assigned but never used.", but I'm actually using the variable. (recommendation appears on line with "$results = $content ..."

      If ($_ -match "#Fields:\s*(.*)"){
        $fields  = $matches[1].split(",") | ForEach-Object{$_.trim()}
        $results = $content | Where-Object{$_ -notmatch "^#"} | ConvertFrom-Csv -Header $fields
      }
    }
    If (-not $results){
      Write-Verbose "Import-CsvFieldsHeader found no valid content in the file, string or array specified."
    }
    $results

[for my reference - line 304 in autopilot.psm1]

Extension version: 2019.9.0
VS Code version: Code 1.39.2 (6ab598523be7a800d7f3eb4d92d7ab9a66069390, 2019-10-15T15:35:18.241Z)
OS version: Windows_NT x64 10.0.17763

[FireInWinter]

I'm seeing the same thing, but in my case it is in the Begin section of Foreach-Object.
1 | ForEach-Object -Begin { $Test=$true } -Process { $Test }

Shows the message "The variable 'Test' is assigned but never used." on the first part where I assign $Test.

[jasonchester]

Also seeing this issue with variable set in Foreach-Object -Begin scriptblock

file content

0..5 | ForEach-Object -Begin { $n = 100 } -Process { $n++ }

❯ Invoke-ScriptAnalyzer .

RuleName : PSUseDeclaredVarsMoreThanAssignments
Severity : Warning
Line     : 1
Column   : 32
Message  : The variable 'n' is assigned but never used.

❯ $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.0.0
PSEdition                      Core
GitCommitId                    7.0.0
OS                             Darwin 19.3.0 Darwin Kernel Version 19.3.0: Thu Jan  9 20:58:23 PST 2020; root:xnu-6153.81.5~1/RELEASE_X86_64
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

❯ Get-Module PSScriptAnalyzer

Name              : PSScriptAnalyzer
Path              : /Users/jason.chester/.local/share/powershell/Modules/PSScriptAnalyzer/1.18.3/PSScriptAnalyzer.psm1
Description       : PSScriptAnalyzer provides script analysis and checks for potential code defects in the scripts by applying a group of built-in or customized rules on the 
                    scripts being analyzed.
Guid              : d6245802-193d-4068-a631-8863a4342a18
Version           : 1.18.3
ModuleBase        : /Users/jason.chester/.local/share/powershell/Modules/PSScriptAnalyzer/1.18.3
ModuleType        : Script
PrivateData       : {PSData}
AccessMode        : ReadWrite
ExportedAliases   : {}
ExportedCmdlets   : {[Get-ScriptAnalyzerRule, Get-ScriptAnalyzerRule], [Invoke-Formatter, Invoke-Formatter], [Invoke-ScriptAnalyzer, Invoke-ScriptAnalyzer]}
ExportedFunctions : {}
ExportedVariables : {}
NestedModules     : {Microsoft.Windows.PowerShell.ScriptAnalyzer}

[bergmeister]

@FireInWinter @jasonchester Your use cases is already reported in issues #1031
The rule is unfortunately limited to the scope of one script block, therefore this might stay an issue for a while

[FireInWinter]

@bergmeister If it is limited to one script block, I would say the rule is fairly useless and should be removed until a solution is found. I see so many false positives on this rule, that it makes using PSScriptAnalyzer annoying to use. Is there at least an easy way to disable the rule without editing files in the mod? If I could set something up in my profile to ignore the rule that would at least make PSScriptAnalyzer useful until this is solved.

[bergmeister]

@FireInWinter We've had this discussion over and over again. Yes, there are some false positives but the rule is still very useful in flagging unused variables. It's just up to you to suppress when you know it is a false positive. If you do not want to keep up with that, use the -ExcludeRule switch on Invoke-ScriptAnalyzer or the equivalent of it in a PSSA settings file, to which you can point the vs-code extension.
Here is an example repo where I show this for a git repo: https://github.com/bergmeister/PSScriptAnalyzer-VSCodeIntegration
For global suppression, set the VS-Code user setting "powershell.scriptAnalysis.settingsPath" to where your PSSA settings file is. The settings file (file extension is .psd1) would have the following content:

@{
    ExcludeRules = @(
        'PSAvoidUsingCmdletAliases'
    )
}

[sba923]

How would I disable the rule for some specific variables / code sections in a PS script that I know trigger a false positive, rather than disabling the rule globally?

[bergmeister]

@sba923 The Readme has a section describing how to suppress them for individual functions or scripts: https://github.com/powershell/psscriptanalyzer#suppressing-rules
For a function, this is how you can suppress for a specific variable (for a script you just put a param() block at the top in order to place the suppression attribute)

function foo {
    [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseDeclaredVarsMoreThanAssignments', 'unused',
        Justification = 'Reason why it is a false positive')]
    param()

    $unused = $null
}

[sba923]

Thanks a bunch for sharing this!