Prioritize validateset completions over Enums for parameters.

[MartinGC94]

PR Summary

Makes tab completion respect validateset values for parameters with an enum type.

function foo
{
    param
    (
        [ValidateSet('DarkBlue','DarkCyan')]
        [ConsoleColor]$Color
    )
}
#Tab completion only cycles through DarkBlue and DarkCyan
foo <Tab>

PR Context

The completion for variables already work this way and Powershell does allow you to use ValidateSet to limit valid enums so this is just a fix for the parameter completion.

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  • Documentation needed
    • Issue filed:
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• Tooling
  • I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
  • OR
  • I have considered the user experience from a tooling perspective and opened an issue in the relevant tool repository. This may include:
    • Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode
      (which runs in a different PS Host).
      • Issue filed:
    • Impact on Completions (both in the console and in editors) - one of PowerShell's most powerful features.
      • Issue filed:
    • Impact on PSScriptAnalyzer (which provides linting & formatting in the editor extensions).
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    • Impact on EditorSyntax (which provides syntax highlighting with in VSCode, GitHub, and many other editors).
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[iSazonov]

What if implement this as filter over enum values? I mean get enum values and filter out them with values from ValidateSet?
This also protects from typos in ValidateSet values.

@mklement0 Are there such scenarios where we could use ValidateSet as follow filter after another source of values?

[mklement0]

I'm not sure we need more sophistication here, as it probably isn't that common a scenario.

No other value sources where filtering based on explicitly enumerated constants - which is the prerequisite for taking effect for tab-completion - come to mind.

The typo problem can be avoided if you use the enum type explicitly, but it's obviously more effort to type:

# A typo here would be flagged in Visual Studio Code and would cause a *parse*-time error when invoked.
[ValidateSet([ConsoleColor]::DarkBlue, [ConsoleColor]::DarkCyan)]

However, if you use strings, you won't see the problem until runtime, situationally, namely only if you happen to pass as value with a typo.

Again, given the use case, I personally think it's fine to make this the command author's responsibility.

On a related note, the ability to rule out specifying multiple values for a flag-based enumeration via a dedicated attribute would be handy - see @SeeminglyScience's suggestions here.

[iSazonov]

What if we use ValidateScript in the scenario?

[vexx32]

ValidateScript doesn't provide any tab completion, so I'm not really sure how it's relevant here.

[iSazonov]

ValidateScript doesn't provide any tab completion, so I'm not really sure how it's relevant here.

My question is about using it as a filter.

[vexx32]

I mean yeah, you can use it as a filter for the enum values as they're passed into the function, but it doesn't have any real advantages over using ValidateSet. You also still can't use it to filter out autocompletion options, which seems to be the point of the PR here.

[iSazonov]

but it doesn't have any real advantages over using ValidateSet.

What if a parameter gets a list of VMs from Cloud but want only stopped ones?

[mklement0]

@iSazonov, in that case you'd use a System.Management.Automation.ArgumentCompleterAttribute attribute.

[iSazonov]

@iSazonov, in that case you'd use a System.Management.Automation.ArgumentCompleterAttribute attribute.

Then it is a binary attribute and you write a script? :-)

[mklement0]

It's usable in PowerShell code too; e.g.:

function foo {
  [cmdletbinding()]
  param(
    [ArgumentCompleter({ param($cmd, $param, $wordToComplete) 'Unix', 'Win32NT' -like "$wordToComplete*" })]
    $Platform
  )
  [System.PlatformID] $Platform
}

Incidentally, this highlights that the [ArgumentCompleter()] attribute too should probably take precedence over the enum values: if you define the $Platform parameter as [System.PlatformID] $Platform, the enum values currently take precedence.

[ghost]

This pull request has been automatically marked as Review Needed because it has been there has not been any activity for 7 days.
Maintainer, please provide feedback and/or mark it as Waiting on Author

[ghost]

This pull request has been automatically marked as stale because it has been marked as requiring author feedback but has not had any activity for 15 days. It will be closed if no further activity occurs within 10 days of this comment.

[MartinGC94]

Why has this been marked as "Waiting on Author"? What do I need to do?

[ghost]

This pull request has been automatically marked as Review Needed because it has been there has not been any activity for 7 days.
Maintainer, please provide feedback and/or mark it as Waiting on Author

[TravisEz13]

I would like to get @daxian-dbw to review this before merging.

[ghost]

This pull request has been automatically marked as Review Needed because it has been there has not been any activity for 7 days.
Maintainer, please provide feedback and/or mark it as Waiting on Author

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🎉v7.3.0-preview.4 has been released which incorporates this pull request.:tada:

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