PowerShell / PowerShell/PSScriptAnalyzer

New Rule: Calling Start-Process without checking ExitCode

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Issue - New Rule
Dominant language
C#
Stars
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Forks
414
Avg merge
13h 1m
Merged PRs (30d)
2

Description

Summary of the new feature
I recently got burned by a library not handling the exit code for Microsoft.PowerShell.Management\Start-Process.

This could be broken into two rules:

  • Always assign Start-Process to a local variable, and check the result. Caveat: How would this work if invoked from Start-Job and deliberately intended to be asynchronous?

Proposed technical implementation details (optional)

  1. Find calls to Microsoft.PowerShell.Management\Start-Process
    There are several ways this could be called:
Arguments not known at caller. No local way to detect $args sets the -Wait and -NoNewWindow switches on
function Do
{
param(
 [hashtable]$StartProcess_params
)
  Microsoft.PowerShell.Management\Start-Process @StartProcess_params
}
Trivial case: Direct arguments
Microsoft.PowerShell.Management\Start-Process -FilePath "cmd.exe" -ArgumentList "/C" -Wait -NoNewWindow
Middle case: arguments constructed in same scope - I believe this is called $script scope
$StartProcess_params = @{
  FilePath = "cmd.exe"
  ArgumentList = "/C"
  RedirectStandardError = $tempErrorFile
  RedirectStandardOutput = $tempOutputFile
  NoNewWindow = $true
  Wait = $true
}
Microsoft.PowerShell.Management\Start-Process @StartProcess_params
Using Start-Job
Start-Job -Name DoSomething -ScriptBlock {
    & cmd.exe /C
    Write-Output $LASTEXITCODE
}
#Do other stuff here
Get-Job -Name DoSomething | Wait-Job | Receive-Job

A clear and concise description of what you want to happen.
Flag as warnings with suggestion to assign call to a PS variable, e.g.:
Microsoft.PowerShell.Management\Start-Process @StartProcess_params
would become:

$process = Microsoft.PowerShell.Management\Start-Process @StartProcess_params
if (-not $process.ExitCode)
{
  Write-Error $(Microsoft.PowerShell.Management\Get-Content $tempErrorFile
}

Alternatively, if the user truly wishes to suppress the result, the UI could offer a "No, I really don't care and want to explicitly say so" command, which would re-write the code to be:

$(Microsoft.PowerShell.Management\Start-Process @StartProcess_params) | Out-Null

or

[void]Microsoft.PowerShell.Management\Start-Process @StartProcess_params

According to StackOverflow, Out-Null adds a 60% overhead and therefore is slower than [void], so we should probably suggest [void]Microsoft.PowerShell.Management\Start-Process @StartProcess_params

What is the latest version of PSScriptAnalyzer at the point of writing
1.17.1

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 reviewing the proposed Microsoft.PowerShell.Management\Start-Process call patterns, including direct arguments, splatted parameters, and Start-Job usage. Resolve whether asynchronous calls and explicit suppression with [void] or Out-Null should be covered, then verify that the resulting rule warns only where the exit result is meant to be checked.

Written by the indexing model from the issue text.

Assessment

Tech stack
powershell
Domain
tooling
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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