Rule Request: UnknownLabel

Not sure whether this is a PowerShell a bug or feature but fixing it in PowerShell would probably be a break change.

In any case, I think unknown labels should be notified and even deserve an error severity if the label doesn't exist or is outside the concerned loop.

Invoke-ScriptAnalyzer -ScriptDefinition {
    :foo foreach ($a in 1,2,3) {
        $a
        if ($a -ge $b) { break bar }
    }
}.ToString()

Expected
Something like:

RuleName           Severity     ScriptName Line  Message
--------           --------     ---------- ----  -------
PSUnknownLabel     Error                   4     The label 'bar' is not known in this context

See also: Pester breaks on functions with unknown label

Start by reproducing the Invoke-ScriptAnalyzer example and inspect how existing rules report control-flow issues. Determine where unknown labels and labels outside the concerned loop are analyzed, then verify that the completed rule reports PSUnknownLabel with Error severity and the expected message for the sample.