Tee Object Respects WhatIf Despite Not Impementing WhatIf

Tee should either implement a WhatIf flag that I can set to -WhatIf:$False or completely ignore WhatIf

Steps to reproduce

https://windowsserver.uservoice.com/forums/301869-powershell/suggestions/15374424-tee-object-doesn-t-work-in-scripts-functions-that

function Test-Tee {
    [Cmdletbinding(supportsshouldprocess)]
    Param()
    $true|tee -Variable b
    $b
}

Test-Tee

Test-Tee -WhatIf

Expected behavior

Return true for both

PS H:\> Test-Tee
True
True

PS H:\> Test-Tee -WhatIf
True
True

Actual behavior

PS H:\> Test-Tee
True
True

PS H:\> Test-Tee -WhatIf
True
What if: Performing the operation "Set variable" on target "Name: b Value: True".

Environment data

Name                           Value                                                                      
----                           -----                                                                      
PSVersion                      5.1.17134.48                                                               
PSEdition                      Desktop                                                                    
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}                                                    
BuildVersion                   10.0.17134.48                                                              
CLRVersion                     4.0.30319.42000                                                            
WSManStackVersion              3.0                                                                        
PSRemotingProtocolVersion      2.3                                                                        
SerializationVersion           1.1.0.1 

Name                           Value
----                           -----
PSVersion                      6.0.2
PSEdition                      Core
GitCommitId                    v6.0.2
OS                             Microsoft Windows 10.0.17134
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[ghost]

+1 just encountered this while trying to implement WhatIf on my own cmdlet.

[Chirishman]

I don’t think you’re getting the point.

With Set-Variable because it does have a settable -WhatIf I can choose to manually exclude it from any wrapping ShouldProcess however because Tee-Object is lacking that parameter I cannot chose to exclude it and thus cannot use it in any function that implements ShouldProcess.

As such the answer by your logic would be “Don’t use Tee-Object”, where I think a better answer is to just fix Tee-Object so that it’s usable, because Tee-Object is a useful tool.