`Select-Object` should be explicit that the input object can be modified

[SteveL-MSFT]

Prerequisites

• [X] Existing Issue: Search the existing issues for this repository. If there is an issue that fits your needs do not file a new one. Subscribe, react, or comment on that issue instead.
• [X] Descriptive Title: Write the title for this issue as a short synopsis. If possible, provide context. For example, "Typo in Get-Foo cmdlet" instead of "Typo."
• [X] Verify Version: If there is a mismatch between documentation and the behavior on your system, ensure that the version you are using is the same as the documentation. Check this box if they match or the issue you are reporting is not version specific.

Links

• https://learn.microsoft.com/en-us/powershell/module/Microsoft.PowerShell.Utility/Select-Object?view=powershell-7.4
• https://github.com/PowerShell/PowerShell/pull/21328
• https://github.com/PowerShell/PowerShell/issues/21308

Summary

The Select-Object docs do not indicate that there are cases where the input object may be modified which can be surprising to users. As the WG-Cmdlets has made a decision to NOT change this behavior as we believe it would likely break folks, we need to document this explicitly.

Details

• See https://github.com/PowerShell/PowerShell/issues/21308

Suggested Fix

Add details to the docs on when the input object can be modified. Add example on how to get the same behavior as ExpandProperty by simply creating a new PSObject "manually" instead of using Select-Object

[sdwheeler]

I will add examples to show the behavior and how to work around the behavior

function Test-Select {
    [PSCustomObject]@{
        "name"="admin1"
        "children"=[PSCustomObject]@{
            "name"="admin2"
        }
    }
}

$obj = Test-Select

New-Object PSObject -Property @{Country = $obj.name; Children=$obj.Children}