PSProvideDefaultParameterValue should automatically ignore mandatory parameters

[mikefrobbins]

When a parameter is set as mandatory, it is not possible to set a default value. If a default value is set for a mandatory parameter, the default value will never be used.

To reproduce the problem, create a function with a mandatory parameter:

function Test-MandatoryParam {
[CmdletBinding()]
param(
[Parameter(Mandatory)]
[String]$Name
)
Write-Output $Name
}

Running Script Analyzer against that function:
Invoke-ScriptAnalyzer -Path C:\tmp\Test-MandatoryParam.ps1

That will give the following warning:
Parameter 'Name' is not initialized. Parameters must have a default value. To fix a violation of this rule, please specify a default value for all parameters.

To show that default values can NOT be used with mandatory parameters, add a default value to the name parameter:

function Test-MandatoryParam {
[CmdletBinding()]
param(
[Parameter(Mandatory)]
[String]$Name = 'Mike'
)
Write-Output $Name
}

Run the function. The default value will not be used and you will be prompted for a value:

PS C:> Test-MandatoryParam
cmdlet Test-MandatoryParam at command pipeline position 1
Supply values for the following parameters:
Name:

Expected behavior is to automatically ignore this rule when a parameter has been defined as mandatory. To be thorough, a rule should exist to give a warning or error when a default value is specified with a mandatory parameter since that value will never be used.

[raghushantha]

Mike. Thank you for the issue.

Will fix the Mandatory parameter issue and create a new warning rule regarding using default values for Mandatory parameters.

[Jaykul]

#362

[mikefrobbins]

I hadn't thought of the larger problem that Joel mentions in issue #362, only the warning I was receiving where it wasn't possible to set a default value. I do agree with Joel as I honestly don't see the value of the PSProvideDefaultParameterValue rule. How does setting a default value have anything to do with best practices?

I do think a rule should exist to warn a user if they're trying to use a default value with a mandatory parameter as previously referenced.

[raghushantha]

Reworked the Mandatory parameter rule as per this thread

#382