The `PSDefaultValue` attribute's `Value` named parameter can cause `Get-Help` to fail if defined as anything other than a string

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues.
• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

According to the PowerShell documentation, the Value named parameter which can be passed to PSDefaultValue() is defined as:

Type: object

This argument specifies a value that is intended to be the default value of a parameter. The value is used in an implementation-defined manner.

Windows PowerShell: The value is used as part of the description of the parameter for the help topic displayed by the Get-Helpcmdlet when the Help property is not specified.

Since it seems to be defined as an arbitrary object, I imagine that one could for instance set the default value as:

Value = [uri]'https://google.com'

However, given a script Get-Foo.ps1 defined as:

<#
    .SYNOPSIS
    Example help
#>
[CmdletBinding()]
[OutputType([void])]
param (
    [PSDefaultValue(Value = [uri]'https://example.com']
    [uri]
    $Baz
)

process {
    Write-Output $Baz
}

Running Get-Help Get-Foo.ps1 -Full causes the Cmdlet to emit an error.

Expected behavior

PS> Get-Help Get-Foo.ps1 -Full


NAME
    get-foo.ps1

SYNOPSIS
    Example help


SYNTAX
    get-foo.ps1 [[-Baz] <Uri>] [<CommonParameters>]


DESCRIPTION


PARAMETERS
    -Baz <Uri>

        Required?                    false
        Position?                    1
        Default value                <Stringified version of the argument passed to the "Value" named parameter>
        Accept pipeline input?       false
        Aliases
        Accept wildcard characters?  false

    <CommonParameters>
        This cmdlet supports the common parameters: Verbose, Debug,
        ErrorAction, ErrorVariable, WarningAction, WarningVariable,
        OutBuffer, PipelineVariable, and OutVariable. For more
    information, see
        about_CommonParameters
    (https://go.microsoft.com/fwlink/?LinkID=113216).

INPUTS

OUTPUTS
    System.Void



RELATED LINKS

Actual behavior

PS> Get-Help Get-Foo.ps1 -Full

Get-Help: Cannot find an overload for ".ctor" and the argument count: "1".

Error details

Message     : Cannot find an overload for ".ctor" and the argument
count: "1".
    Source      : System.Management.Automation
    HResult     : -2146233087
    StackTrace  :
   at
System.Management.Automation.Language.Compiler.GetAttribute(AttributeAst
attributeAst)
   at System.Management.Automation.Language.Compiler.GetRuntimeDefinedParam
eter(ParameterAst parameterAst, Boolean& customParameterSet, Boolean&
usesCmdletBinding)
   at System.Management.Automation.Language.Compiler.GetParameterMetaData(R
eadOnlyCollection`1 parameters, Boolean automaticPositions, Boolean&
usesCmdletBinding)
   at
System.Management.Automation.CompiledScriptBlockData.InitializeMetadata()
   at System.Management.Automation.CompiledScriptBlockData.get_CmdletBindin
gAttribute()
   at System.Management.Automation.CommandMetadata..ctor(ScriptBlock
scriptblock, String commandName, ExecutionContext context)
   at System.Management.Automation.ExternalScriptInfo.get_CommandMetadata()
   at System.Management.Automation.HelpCommentsParser..ctor(CommandInfo
commandInfo, List`1 parameterDescriptions)
   at System.Management.Automation.HelpCommentsParser.CreateFromComments(Ex
ecutionContext context, CommandInfo commandInfo, List`1 comments, List`1
parameterDescriptions, Boolean dontSearchOnRemoteComputer, String&
helpFile, String& helpUriFromDotLink)
   at
System.Management.Automation.CommandHelpProvider.GetHelpInfo(CommandInfo
commandInfo, Boolean reportErrors, Boolean searchOnlyContent)
   at
System.Management.Automation.CommandHelpProvider.SearchHelp(HelpRequest
helpRequest, Boolean searchOnlyContent)+MoveNext()
   at System.Management.Automation.HelpSystem.SearchHelp(HelpRequest
helpRequest)+MoveNext()
   at System.Management.Automation.HelpSystem.DoGetHelp(HelpRequest
helpRequest)+MoveNext()
   at Microsoft.PowerShell.Commands.GetHelpCommand.ProcessRecord()
   at System.Management.Automation.CommandProcessor.ProcessRecord()
CategoryInfo          : NotSpecified: (:) [Get-Help], MethodException
FullyQualifiedErrorId :
MethodCountCouldNotFindBest,Microsoft.PowerShell.Commands.GetHelpCommand
InvocationInfo        :
    MyCommand        : Get-Help
    ScriptLineNumber : 1
    OffsetInLine     : 1
    HistoryId        : 2
    Line             : get-help get-foo.ps1 -Full
    Statement        : get-help get-foo.ps1 -Full
    PositionMessage  : At line:1 char:1
                       + get-help get-foo.ps1 -Full
                       + ~~~~~~~~~~~~~~~~~~~~~~~~~~
    InvocationName   : get-help
    CommandOrigin    : Internal
ScriptStackTrace      : at <ScriptBlock>, <No file>: line 1

Environment data

Name                           Value
----                           -----
PSVersion                      7.6.0-preview.2
PSEdition                      Core
GitCommitId                    7.6.0-preview.2
OS                             Microsoft Windows 10.0.26100
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

Start by reproducing the Get-Help failure with the PSDefaultValue(Value = [uri]'https://example.com') script shown in the issue. Trace the metadata path through Compiler.GetAttribute and verify that Get-Help -Full succeeds for non-string Value arguments while displaying a stringified default value.