Add ErrorView to SpecialVars.cs

[ewisniew0]

PR Summary

Fixes #1749
No warning is issued for Errorview by rule PSUseDeclaredVarsMoreThanAssignment

• Added ErrorView to SpecialVars.cs
• Added test for warning mentioned in issue

Additional Notes

I could not use the correct type for ErrorView as the type ErrorView is not available in PS3 and instead declared it's type as an Enum.
However I found that inside SpecialVars.cs the array of types : Type[] PreferenceVariableTypes , is not used anywhere, so is there a reason for it to exist?

PSScriptAnalyzer/Engine/SpecialVars.cs

Line 107 in 77f6500

internal static readonly Type[] PreferenceVariableTypes = new Type[]

PR Context

When we try to assign a new state to a Preference Variable like ErrorView it should not be flagged as a warning by the rule PSUseDeclaredVarsMoreThanAssignment. In order to prevent the rule from showing this warning there is a check for built in variables:

PSScriptAnalyzer/Rules/UseDeclaredVarsMoreThanAssignments.cs

Line 203 in 77f6500

if (Helper.Instance.HasSpecialVars(varKey))

This checks for the presence of the Preference Variable's declaration inside the SpecialVars.cs file. If it's in that file PSUseDeclaredVarsMoreThanAssignment stops throwing the warning.

PR Checklist

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• 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
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[bergmeister]

There is PSV3 variable defined as we do conditional compilation for each version of PS (3, 4, 5 and 'Core'). You could use this to use Enum only for the v3 compiled version but the correct types for others.

[ewisniew0]

Okay I can do that, however I'm still not sure why this type array is here since nobody seems to reference it, should it be expanded despite this?

[Jaykul]

@bergmeister @JamesWTruher what is the point of this enum? Can we just delete the whole thing, and merge this PR already?

[bergmeister]

@Jaykul Whilst it's not directly referenced, it is still needed as it clearly solves the issue of not flagging false positive for ErrorView. I presume the rule is using reflection. The PSV3 variable is a pragma, i.e. a build time variable as we use different PowerShell version SDKs when we build against the different versions.

[Jaykul]

Honestly, maybe we should probably just type this as string.

The ErrorView enum is new in PS7 and it's not enforced. The variable can be overwritten, and now that it's an Enum in PS7, it has to be overwritten by anyone who wants to improve the error view (such as my ErrorView module, which actually works on old versions of PowerShell)...

[bergmeister]

Overall looks good, thanks. Just one idea around the type problem you mentioned