Add the AvoidExclaimOperator rule to warn about the use of the ! negation operator. Fixes #1826

[Liam Peters (liamjpeters)]

Add a rule to warn about using the exclamation mark (!) as the negation operator. Suggests using -not instead.

PR Summary

Add the PSAvoidExclaimOperator rule to warn about the use of ! for negation. The rule is disabled by default as many people see this as a stylistic preference. Covered by tests .Fixes #1826

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
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[Liam Peters (liamjpeters)]

@microsoft-github-policy-service agree

[Liam Peters (liamjpeters)]

Christoph Bergmeister (@bergmeister) - 👋 Can I get a review please? Sorry I didn't see a way to add a reviewer myself 😊 Thanks!

[Christoph Bergmeister (bergmeister)]

Looks good overall, just a few comments. Not sure on the rule name though, it's definitely rather exclamation mark and not exclamation point. Maybe even as short as ExclaimOperator, since that is the name of the token.

[Liam Peters (liamjpeters)]

Renamed rule from AvoidExclamationPointOperator to AvoidExclaimOperator

[Liam Peters (liamjpeters)]

Christoph Bergmeister (@bergmeister) - Thanks for your feedback so far - really helpful 😀. Was there anything else that needs to change for this to be considered for a merge? Anyone else I should be asking for a review from?

[Christoph Bergmeister (bergmeister)]

Added James as well to review. Other than that I just want to test drive it a bit myself for some exploratory testing as the rule is disabled by default so wouldn't get exercised as part of existing test suite scenarios

[Liam Peters (liamjpeters)]

Any news on this? I don't really know what my expectations should be, as this is my first contribution to this project - so please feel free to tell me to cool my jets and just be more patient.

I appreciate this PR doesn't introduce some killer feature that will be used by loads of people - but I'm excited for it and don't want the PR to be abandoned. Equally I'm excited to pick up other issues and open more PRs to improve the tool and my own c#, after testing the waters here.

Is there anything I can do to help?

[Christoph Bergmeister (bergmeister)]

Sorry for the delay Liam Peters (@liamjpeters) . It's not a bumper feature but because it can run on any PowerShell code, it's easy to miss a case that could result e.g. in a NullReferenceException. But the feature is not enabled by default, which is great to limit blast radius.
There's actually one thing you could help with, could you run PSSA with this rule enabled against a more complex script like this one as a one off and check there are no exceptions https://github.com/PowerShell/PowerShell/blob/master/build.psm1
Then happy to merge, the rest of the code looks good to me :-)

[Liam Peters (liamjpeters)]

Christoph Bergmeister (@bergmeister) - Good idea to run it on a more complex test file.

I've run the existing and updated PSSA against the Powershell project's build file. No exceptions thrown and no difference in execution time (both take an average of 170ms on my machine over multiple runs - even with my additional rule enabled).

Invoke-ScriptAnalyzer -Path .\build.psm1 -Settings @{Rules = @{ 'PSAvoidExclaimOperator' = @{ Enable = $true }}}

The build file has a mix of usages of -not and ! so is a good candidate. Using a text search there are 33 instances of the "!" character, 9 of them are within strings or comments (leaving 24 being used as negation).

PSSA with the rule enabled correctly flags the 24 negation instances.

Calling Invoke-ScriptAnalyzer with -Fix correctly changes the 24 negation instances.

Anything else you can think I should check - please let me know.