PowerShell / PowerShell/PSScriptAnalyzer

PSAvoidAssignmentToAutomaticVariable generates false positives during script analysis

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Area - Rules Issue - Bug Need Repro Info
Dominant language
C#
Stars
2.2k
Forks
414
Avg merge
13h 1m
Merged PRs (30d)
2

Description

Steps to reproduce

Run this function through PSSA.

function Write-Log {
    [CmdletBinding()]
    param
    (
        [Parameter(Position = 0, Mandatory)]
        [ValidateNotNullOrEmpty()]
        [string]
        $Message,

        [switch]
        $Error
    )
    $callerEAP = $ErrorActionPreference
    try {
        $messageColor = if ($PSCmdlet.MyInvocation.BoundParameters.ContainsKey('Error') -and $Error) {
            [ConsoleColor]::Red
        } else {
            [ConsoleColor]::Cyan
        }

        Write-Host -Foreground $messageColor -Object $Message

        # Reset colors to return to default after an error message on a compilation error
        [System.Console]::ResetColor()
    } catch {
        Write-Error -ErrorRecord $_ -ErrorAction $callerEAP
    }
}

Expected behavior

It passes.

Actual behavior

PSSA reports the following:

The Variable 'Error' cannot be assigned since it is a readonly automatic variable that is built into PowerShell, please use a different name.

There are a number of problems with this:

  1. The comma should be a period for it to read properly.
  2. The error text is incorrect. $Error can be assigned in child scopes without issue. $Error is read-only only in the global scope, and errors are automatically written into that globally-scoped collection that is read-only from PowerShell. In functions, or child scopes, you can use a $Error variable to your hearts content.
  3. Most importantly: the issue that is being called out by PSSA here should not be called out at all.

Environment data

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      7.0.1
PSEdition                      Core
GitCommitId                    7.0.1
OS                             Microsoft Windows 10.0.18363
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0
> (Get-Module -ListAvailable PSScriptAnalyzer).Version | ForEach-Object { $_.ToString() }
1.19.0

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the supplied Write-Log function through PSScriptAnalyzer and inspect the PSAvoidAssignmentToAutomaticVariable rule that reports the $Error parameter. Confirm the diagnostic against the stated PowerShell scoping behavior; done means this case is not reported and the diagnostic text is corrected if it remains applicable elsewhere.

Written by the indexing model from the issue text.

Assessment

Tech stack
csharp, powershell
Domain
tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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