Throw a warning when I redefine a global variable in a local scope

Like the title says, it would be useful if I was warned whenever I try to reuse a global variable's name in a more local scope.

$a = 'Unchanged'
function foo {
    Write-Host "foo can read `$a : `$a = $a"
    $a = 'Changed from foo' # this should be warning!!
    Write-Host "foo can change it's own copy of `$a: `$a = $a"
}
foo
Write-Host "After foo call: `$a = $a"

Thanks to @vors for the example.

以 issue 中的 PowerShell 示例作为行为起点。检查 PSScriptAnalyzer 如何报告与作用域相关的诊断，然后定义警告触发条件，并使用所演示的全局变量和局部变量案例进行验证。