PR Summary

Fixes IHostUISupportsMultipleChoiceSelection.PromptForChoice over PowerShell remoting when defaultChoices is anything other than a Collection<int> or $null. There are two fixes in this commit.

The first is to make sure that PromptForChoice serializes the defaultChoices value as Collection<int>. This ensures that unpatched clients connecting to a patched server can deserialize the expected value for this argument.

The second is to support decoding a host method array value when the expected type is IEnumerable<int>. This ensures that patches clients connecting to an unpatched server can deserialize the array serialized value.

PR Context

Calling the multiple-choice PromptForChoice overload directly in a local session when using [int[]] for defaultChoices works out of the box:

$choices = [System.Management.Automation.Host.ChoiceDescription[]]@('&Apple', '&Banana', '&Cherry')
$Host.UI.PromptForChoice('Fruit', 'Pick one or more', $choices, [int[]]@(0, 2))

Calling the same overload in a remote PSSession with an int[] for defaultChoices fails. The script below reproduces it without any WinRM or SSH setup by opening a named-pipe session back to the current process:

$connInfo = [System.Management.Automation.Runspaces.NamedPipeConnectionInfo]::new($PID)
$runspace = [runspacefactory]::CreateRunspace($Host, $connInfo)
$runspace.Open()
$session = [System.Management.Automation.Runspaces.PSSession]::Create($runspace, 'NamedPipe', $null)

Invoke-Command -Session $session -ScriptBlock {
    $choices = [System.Management.Automation.Host.ChoiceDescription[]]@('&Apple', '&Banana', '&Cherry')
    $Host.UI.PromptForChoice('Fruit', 'Pick one or more', $choices, [int[]]@(0, 2))
}

$session | Remove-PSSession

Before this change:

After this change:

RemoteHostEncoder chooses the wire format from the value's runtime type when encoding, but the client decodes using the method's declared parameter type. The defaultChoices parameter is declared as IEnumerable<int>, and the client always decoded it as a Collection<int> (an ArrayList on the wire). An int[] is encoded with the array format (mae/mal properties), so the server serializes and sends the call without error and the client then fails to decode it. Other types such as List<int> fail earlier, on the server, with "Remote host method data encoding is not supported for type ...".

Passing an array is the usual case due to the simplicity in declaring [int[]] over [Collections.ObjectModel.Collection[int]]. So in practice this API only worked remotely when defaultChoices was $null or an explicit Collection<int>.

This behaviour dates back to Windows PowerShell 5.1 so is present in all of 7.x.

PR Checklist

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