SupportsShouldProcess does not create $Confirm in a way recognized by Strict Mode

Steps to reproduce

Set-StrictMode -Version:Latest

function Test-ShouldProcess {
    [CmdletBinding(
        SupportsShouldProcess,
        ConfirmImpact = 'High'
    )]
    param(
        [Switch]$Force
    )

    if ($Force -and -not $Confirm){
        $ConfirmPreference = 'None'
    }

    if ($PSCmdlet.ShouldProcess('TARGET')){
        Write-Output "Some Action"
    }
}

Test-ShouldProcess -Force

Actual behavior

InvalidOperation: C:\temp\testsp.ps1:12
Line |
  12 |      if ($Force -and -not $Confirm){
     |                           ~~~~~~~~
     | The variable '$Confirm' cannot be retrieved because it has not been set.

This error does not occur when Strict Mode is off. If you try to add $Confirm as a switch parameter you get the following error:

Test-ShouldProcess: C:\temp\testsp.ps1:22
Line |
  22 |  Test-ShouldProcess -Force -confirm:$true
     |  ~~~~~~~~~~~~~~~~~~
     | A parameter with the name 'Confirm' was defined multiple times for the command.

So Strict Mode does not see that $Confirm has been defined, but SupportsShouldProcess does not allow you to define it.

Environment data

This was tested in PowerShell 5.1 and 7.1.

[SeeminglyScience]

Yeah. Creating a variable for the actual switch parameter wouldn’t make sense because a parameter isn’t the only way these things are scoped. Verbose, warning, whatif, debug, confirm, etc are all propagated via the preference variables and also to child scopes and cmdlet calls.

Force is different because it’s purely convention.

[SeeminglyScience]

@sdwheeler A parameter is defined, but it is not translated into a variable. Same way other common parameters work like -Verbose, there’s no $Verbose variable created.

The example should be more like this:

if ($Force -or $PSCmdlet.ShouldProcess('Target')) {
  # do thing
}