Working with the Ast

Synopsis

Shows how to react to the entire pipeline.

Description

For some seriously advanced tab completion, you can parse the current pipeline and react to commands before and after the command for which you want to complete a parameter's value. For this you have access to the full Ast via the $commandAst variable.

An non-hardened example that picks up on the properties of the output type of the preceding command:

Register-PSFTeppScriptBlock -Name MyModule.IncomingProperties -ScriptBlock {
    $command = $commandAst.Parent.Parent.Statements.PipelineElements[-2].CommandElements | Where-Object { $_ -is [System.Management.Automation.Language.StringConstantExpressionAst] } | Select-Object -First 1 -ExpandProperty Value
    $cmd = Get-Command $command
    if ($cmd.CommandType -eq "Alias") { $cmd = $cmd.ResolvedCommand }
    $cmd.OutputType.Type | ForEach-Object { $_.GetProperties() } | Select-Object -ExpandProperty Name -unique | Sort-Object
}

Note: The above is not robust to many scenarios and may fail (though it will do no harm when it does). This is meant purely as a Proof of Concept.