Register-ArgumentCompleter doesnt give completions in the editor

[PrzemyslawKlys]

Issue Description

Register-AutoCompleter doesn't seem to work properly in VSCode. It only works for single string.

function Test-Meteor {
    param(
        [validateset('Test','Test2','Test3')][string[]] $Value,
        [string[]] $OtherValue
    )


}


[scriptblock] $Test = {
    param($commandName, $parameterName, $wordToComplete, $commandAst, $fakeBoundParameters)

    @('Test','Test1','Test2')
}

Register-ArgumentCompleter -CommandName Test-Meteor -ParameterName OtherValue -ScriptBlock $Test


Test-Meteor -Value Test,Test2 -OtherValue Test1

This works fine when you try in VScode Terminal (even the Powershell Integrated one) or outside of VSCode. Sometimes it starts working but only for 1st value, 2nd value is loaded from cache along with some garbage.

Attached Logs

Follow the instructions in the README about
capturing and sending logs.

Environment Information

Visual Studio Code

Name	Version
Operating System	Windows_NT x64 10.0.18362
VSCode	1.37.1
PowerShell Extension Version	2019.5.0

PowerShell Information

Name	Value
PSVersion	5.1.18362.145
PSEdition	Desktop
PSCompatibleVersions	1.0 2.0 3.0 4.0 5.0 5.1.18362.145
BuildVersion	10.0.18362.145
CLRVersion	4.0.30319.42000
WSManStackVersion	3.0
PSRemotingProtocolVersion	2.3
SerializationVersion	1.1.0.1

Visual Studio Code Extensions

Visual Studio Code Extensions(Click to Expand)

Extension	Author	Version
auto-rename-tag	formulahendry	0.1.0
beautify	HookyQR	1.5.0
bracket-pair-colorizer-2	CoenraadS	0.0.28
code-settings-sync	Shan	3.4.2
githistory	donjayamanne	0.4.6
gitlens	eamodio	9.9.3
html-css-class-completion	Zignd	1.19.0
live-html-previewer	hdg	0.3.0
markdown-all-in-one	yzhang	2.4.2
markdown-preview-enhanced	shd101wyy	0.4.3
markdown-shortcuts	mdickin	0.11.0
material-icon-theme	PKief	3.9.0
powershell	ms-vscode	2019.5.0
project-manager	alefragnani	10.7.0
theme-monokai-pro-vscode	monokai	1.1.14
vscode-html-css	ecmel	0.2.3
vscode-wakatime	WakaTime	2.2.0
xml	DotJoshJohnson	2.5.0

[SydneyhSmith]

@PrzemyslawKlys thanks for opening this bug and providing detailed repro steps--we were able to reproduce this issue...we will have to do some more investigation as to where the connection is missing to provide the editor with this context

[PrzemyslawKlys]

Just so you know the same problem most likely relates to:

        [ArgumentCompleter(
            {
                param($CommandName, $ParameterName, $WordToComplete, $CommandAst, $FakeBoundParameters)
                ((Get-EventsDefinitions).Keys)
            }
        )]
        [ValidateScript(
            {
                $_ -in (((Get-EventsDefinitions).Keys))
            }
        )]

I remember having issues with it. It also impacts dynamic parameters.

    DynamicParam {
        # Defines Report / Dates Range dynamically from HashTables and saved files
        $ParameterSetsAttributesDateManual = New-Object System.Management.Automation.ParameterAttribute
        $ParameterSetsAttributesDateManual.Mandatory = $true
        $ParameterSetsAttributesDateManual.ParameterSetName = 'DateManual'

        $ParamAttribDatesRange = New-Object System.Management.Automation.ParameterAttribute
        $ParamAttribDatesRange.Mandatory = $true
        $ParamAttribDatesRange.ParameterSetName = 'DateRange'

        $ParameterSetsAttributes = New-Object System.Management.Automation.ParameterAttribute
        $ParameterSetsAttributes.Mandatory = $true
        $ParameterSetsAttributes.ParameterSetName = 'Manual'

        # Definitions for Report
        $Names = (Get-EventsDefinitions).Keys
        $ReportAttrib = New-Object  System.Collections.ObjectModel.Collection[System.Attribute]
        $ReportAttrib.Add($ParameterSetsAttributes)
        $ReportAttrib.Add($ParamAttribDatesRange)
        $ReportAttrib.Add($ParameterSetsAttributesDateManual)
        $ReportAttrib.Add((New-Object System.Management.Automation.ValidateSetAttribute($Names)))
        $ReportRuntimeParam = New-Object System.Management.Automation.RuntimeDefinedParameter('Report', [string[]], $ReportAttrib)

        # Definitions for Dates Range
        $DatesRange = (Get-DatesDefinitions -Skip 'CustomDate', 'CurrentDayMinuxDaysX', 'CurrentDayMinusDayX', 'OnDay')
        $DatesRangeAttrib = New-Object  System.Collections.ObjectModel.Collection[System.Attribute]
        $DatesRangeAttrib.Add($ParamAttribDatesRange)
        $DatesRangeAttrib.Add((New-Object System.Management.Automation.ValidateSetAttribute($DatesRange)))
        $DatesRangeRuntimeParam = New-Object System.Management.Automation.RuntimeDefinedParameter('DatesRange', [string], $DatesRangeAttrib)

        # Finalization
        $RuntimeParamDic = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary
        $RuntimeParamDic.Add('Report', $ReportRuntimeParam)
        $RuntimeParamDic.Add('DatesRange', $DatesRangeRuntimeParam)
        return $RuntimeParamDic
    }

Sorry that I didn't provide a "test" but if it's needed I can provide some minified versions.

[M1kep]

Could this introduce a security concern of code running simply by attempting to do ArgumentCompletion within VSCode editor? Should the editor environment be considered a "no run" area, unless explicitly requested?

[M1kep]

When the code is run in the Integrated Console it looks like the Intellisense engine "overwrites" or "prefers" the autocompletion with the in-file definition. Which means that the values aren't known due to the issue stated in #831