Rule Proposal: Warn on dot-sourced function

I've inherited a project where everything is in, for lack of a better description, undeclared global scope, spread across several files. Functions don't have always have parameters, and are called with a dot before the function name. Variables are treated as global, though not declared. For example:

c:\Utils.ps1

function Write-MyLog {
$itemToLog | out-file c:\mylog.txt -append
}

c:\Interface.ps1

. c:\Utils.ps1

$itemToLog = "Something happened"
. Write-MyLog

Miraculously, this all works. Of course, I dare not change anything.

I would love it if ". Write-MyLog" came up as a warning, and even more so if there were some indication that "$itemToLog" in C:\Interface.ps1 was being used by the function called from c:\Utils.ps1.

Start by reproducing the behavior in the example c:\Utils.ps1 and c:\Interface.ps1 scripts, focusing on the dot-sourced function call and the cross-file $itemToLog variable. Done means the analyzer warns on the requested construct and provides the requested indication of variable usage, with the scope and expected diagnostics agreed.