`New-HelpCabinetFile` fails on Windows PowerShell 5.1 because `$IsWindows` is undefined

[kborowinski]

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest version
• Search the existing issues.

Steps to reproduce

New-HelpCabinetFile currently checks whether the platform is Windows by using the $IsWindows automatic variable:

if (! $IsWindows) {
    throw "'New-HelpCabinetFile' is only supported on Windows."
}

However, $IsWindows is only available in PowerShell Core and is not defined in Windows PowerShell 5.1.

As a result, running New-HelpCabinetFile on Windows PowerShell 5.1 fails even though the cmdlet is intended to be supported on Windows.

Expected behavior

New-HelpCabinetFile should run successfully on Windows PowerShell 5.1.

Actual behavior

The cmdlet fails because $IsWindows is not defined in Windows PowerShell 5.1.

Error details

New-HelpCabinetFile -CabinetFilesFolder D:\TMP\ -MarkdownModuleFile D:\TMP\tmp.md -OutputFolder $PWD
'New-HelpCabinetFile' is only supported on Windows.
At C:\Program Files\WindowsPowerShell\Modules\Microsoft.PowerShell.PlatyPS\1.0.1\Microsoft.PowerShell.PlatyPS.psm1:277 char:13
+             throw "'New-HelpCabinetFile' is only supported on Windows ...
+             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : OperationStopped: ('New-HelpCabine...ted on Windows.:String) [], RuntimeException
    + FullyQualifiedErrorId : 'New-HelpCabinetFile' is only supported on Windows.

Environment data

Name                           Value
----                           -----
PSVersion                      5.1.26100.8328
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0, 5.0, 5.1.26100.8328}
BuildVersion                   10.0.26100.8328
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

Version

1.0.1

Visuals