PR Summary

This PR fixes the following longstanding issue: #1300 (Global variables are erroneously reported as "never used")

The issue exists because Helper.IsVariableGlobalOrEnvironment uses an Ast to key into VariableAnalysisDictionary, calling VariableAnalysis.IsGlobalOrEnvironment on the value returned to determine whether or not the variable is a global. However, in some cases, the key does not exist in the dictionary, resulting in the method returning false. Fortunately, VariableAnalysis.IsGlobalOrEnvironment depends on no instance members, instead relying solely on the properties of VariableExpressionAst, which is passed in. As such, VariableAnalysis.IsGlobalOrEnvironment can be made static with no consequence, allowing Helper.IsVariableGlobalOrEnvironment to call the method without the dictionary operations.

Also of note, the current implementation is somewhat redundant, with UseDeclaredVarsMoreThanAssignments.AnalyzeScriptBlockAst checking VariablePath.DriveName separately, which is why the issue does not affect environment variables despite VariableAnalysis.IsGlobalOrEnvironment erroneously returning false in some cases.

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.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.