New Rule Suggestion: ParameterSetName mismatch.

[Jaykul]

When there is a DefaultParameterSetName, we need a rule to detect if there is not a case-sensitive exact match between that value and a ParameterSetName.

People aren't used to PowerShell being case-sensitive, but it is, in this case.

If there is a match with the wrong case, this is an Error, if there's no match at all, then this is probably just informational (it's relatively common to have the default be an un-named parameter set, right?).

[KirkMunro]

+1 for the case sensitive match failure generating an error.

The test should simply look for ParameterSetName values that match DefaultParameterSetName values with a case-insensitive search, and then error on any that don't also match with a case-sensitive search.

@Jaykul, I haven't tried this, but presumably this would also be an issue between ParameterSetName values as well, right? So having two parameters with the same-but-not-case-sensitive-matching parameter set name would end up with two different parameter sets? In which case, this rule should error for those as well if they don't have a case sensitive match.

I don't know if it is common to leave out DefaultParameterSetName when you are using parameter sets. I have done it in the past, but not in recent years. It is done though, and possibly unintentionally, so I agree an informational message when DefaultParameterSetName is not applied when parameter sets are used would be appropriate.

[KirkMunro]

Actually, I did some more looking, and through all of the modules I have on my system, my own and many dozen downloaded from the Gallery, and there are very few (7 out of 130) that use parameter sets that don't define a DefaultParameterSetName value. For those that do, some of them appear buggy or to have a very poor design. With that in mind, I think it would be better to warn if DefaultParameterSetName is not used when there are multiple parameter sets are defined, leaving it to the author to indicate if it's not really a warning or not by disabling the rule for that command. That perspective is only based on the modules I have reviewed this morning. @Jaykul, how common is it in the modules on your system to use parameter sets without defining a DefaultParameterSetName?

[rkeithhill]

+1 for the case mismatch issue.

[Jaykul]

@KirkMunro It's almost mandatory to specify the DefaultParameterSetName, but it is only actually mandatory if there is not a unique, mandatory parameter in each ParameterSet.

The rule I suggested could be enhanced to check for more correctness, but I'm afraid that at some point it becomes a matter of just informing the user how PowerShell is parsing their command (i.e. listing the $Command.ParameterSets | % ToString with their names, and asking for a review).

As I understand it, there are things you can assume are mistakes:

• ParameterSetName which matches another if you ignore case, but don't otherwise. This is always an error.
• DefaultParameterSetName which matches a ParameterSetName if you ignore case, but doesn't otherwise. This is always an error.
• ParameterSets that don't have at least one unique parameter. This is always an error.

And other things which might be mistakes:

• Not explicitly defining a default parameter set should generate a warning. It's a readability/maintainability problem.
• Setting the DefaultParameterSetName to a name that isn't used (other than something like "Default") should generate an information log. It's possibly confusing to future editors, but perfectly valid if there are parameters which are not explicitly assigned to any parameter set, or if the command can be run with no parameters...
• ParameterSets that don't have at least one unique, parameter that is mandatory are usually a mistake (should generate a warning?) but are still valid.
• ParameterSets where the unique parameters aren't used in the command (and where the ParameterSetName isn't checked by name) might indicate un-implemented features (should probably generate a warning), but are still valid.

... I'm sure I had another couple warnings in mind, but I can't think what they are