Unable to Resolve Parameter Set When Dynamic Parameter Qualifies Parameter Set about powershell HOT 5 CLOSED

Thank you for your help and information! It is greatly appreciated!

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The immediate problem is that -String2 and -Type cannot be combined unambiguously, causing parameter binding to stop right there - your DynamicParam block is never called.

To at least eliminate the "parameter set cannot be resolved error", comment out the [Parameter()] attribute that contains ParameterSetName = 'DynamicA-String2' that decorates the $String2 parameter.

It looks like you can greatly reduce the number of parameter sets, which will likely also solve your problem.

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In other words, dynamic parameters cannot be used to make a parameter set unambiguous, requiring the static parameters to unambiguously select a parameter set.

I was able to change the dynamic parameter to not set the ParameterSetName, which allowed for the reduction of parameter sets to resolve. However, I want to know if this was a bug or if it was by design. It sounds like it is by design.

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In other words, dynamic parameters cannot be used to make a parameter set unambiguous, requiring the static parameters to unambiguously select a parameter set.

That's a great summary. Yes, any given static parameters must resolve unambiguously to a parameter set first.

While I cannot speak in any official capacity, I do think that this is by design, given the stages of parameter binding described by a team member in #14701 (comment) - also see the clarification in #14701 (comment).

Here's what I think is a minimal example:

function Test-AmbiguousParameter {
  [CmdletBinding(DefaultParameterSetName = 'Default')]
  param (
    [Parameter(Mandatory = $true, ParameterSetName = 'Default')]
    $A,

    [Parameter(Mandatory = $false, ParameterSetName = 'Other')]
    $B
  )

  DynamicParam {
    Write-Verbose -Verbose HERE
  }

  process {
    Write-Output $PSCmdlet.ParameterSetName
  }

}

Test-AmbiguousParameter -a 1 -b 2 predictably yields the "parameter set cannot be resolved" error and never prints the VERBOSE: HERE message, implying that the DynamicParam block is never invoked.

Contrast with Test-AmbiguousParameter -a 1 and Test-AmbiguousParameter -b 2

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