IDLE/pyclbr failures for __main__

Bug report

This discuss post says that IDLE's module browser, which uses pyclrb, fails if the file name is __main__, the filename has a '.', or the file has a syntax error. The first is the fault of of importlib.util._find_spec_from_path('main') failing (##117742). I need to verify the second. The third is a result of switching from custom parsing code that passed over syntax errors to ast.parse which does not -- and not noticing the possibility of exceptions and taking them into account. Since IDLE seems to hang, it is not clear where, and whether IDLE gets the exception.