Fix PowerShell@2 showWarnings to respect WarningAction preferences

[Copilot]

Problem

When using the PowerShell@2 task with showWarnings: true, the task incorrectly displays ALL warnings as Azure DevOps warnings, even when they should be suppressed using:

• -WarningAction SilentlyContinue
• -WarningAction Ignore
• Stream redirection operators (3> $null, 3> file.txt)

This causes massive log clutter when users want to surface some warnings but suppress others.

Before this fix:

- task: PowerShell@2
  inputs:
    showWarnings: true
    script: |
      Write-Warning "Should show"
      Write-Warning "Should NOT show" -WarningAction SilentlyContinue
      Write-Warning "Should NOT show" -WarningAction Ignore
      Write-Warning "Should NOT show" 3> $null

Results in 4 Azure DevOps warnings (incorrect behavior).

Root Cause

The original implementation used -WarningVariable +warnings which captures warnings before PowerShell's preference system processes them, bypassing all warning suppression mechanisms.

# Old broken approach
Invoke-Command {$script} -WarningVariable +warnings

Solution

Replace the WarningVariable approach with PowerShell stream redirection that respects the built-in warning preference system:

# New fixed approach  
& $originalContents 3>&1 | ForEach-Object {
    if ($_ -is [System.Management.Automation.WarningRecord]) {
        Write-Host "##vso[task.logissue type=warning;]$_"
    } else {
        $_
    }
}

After this fix:
The same script now shows 1 Azure DevOps warning (correct behavior).

Changes Made

• powershell.ps1: Updated PowerShell implementation to use stream 3 capture
• powershell.ts: Updated TypeScript implementation for consistency
• L0ShowWarnings.ts: Added comprehensive test case validating the fix
• L0.ts: Integrated new test into the test suite

Validation

✅ Default warnings properly shown as Azure DevOps warnings
✅ -WarningAction SilentlyContinue warnings correctly suppressed
✅ -WarningAction Ignore warnings correctly suppressed
✅ Stream redirected warnings correctly suppressed
✅ Global $WarningPreference settings respected
✅ Existing functionality preserved when showWarnings: false

Fixes #20851.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• 03nvsblobprodwcus014.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 055vsblobprodwcus02.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)
  • Triggering command: npm install (dns block)
• 1g1vsblobprodwcus01.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 3eavsblobprodwcus03.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 3zgvsblobprodwcus024.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)
  • Triggering command: npm install (dns block)
• 40qvsblobprodwcus022.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 4fdvsblobprodwcus012.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 5tbvsblobprodwcus06.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 61cvsblobprodwcus010.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 73dvsblobprodwcus07.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 8usvsblobprodwcus011.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• 9owvsblobprodwcus020.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• arpvsblobprodwcus017.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• crcvsblobprodwcus021.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• fslvsblobprodwcus015.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• grnvsblobprodwcus04.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• k92vsblobprodwcus08.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• mnzvsblobprodwcus05.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)
• pl8vsblobprodwcus09.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• uubvsblobprodwcus018.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• vwmvsblobprodwcus016.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• x4wvsblobprodwcus013.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• xg1vsblobprodwcus019.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)
• xlkvsblobprodwcus023.vsblob.vsassets.io
  • Triggering command: npm install (dns block)
  • Triggering command: npm install (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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