The Xref magic spell?

[Joe Armstrong]

  I have a directory with some Erlang modules in it.

  These modules calls things in the standard libraries.

  Is there  a simple one-liner/script/anything  that runs Xref  on the
code in my directory and warns me about possibly missing functions?

  I got this far:

	> {ok, P} = xref:start(a).
	...
	> xref:add_directory(P, ".", []).
	Skipping ./base64.beam (no debug information)
        Skipping ./ec4.beam (no debug information)
	...

   After a cursory reading of the xref manual it seems that
modules have to be debug compiled, but there appears to be
no flag in erlc to do this.

   Any ideas??

   Thanks

   /Joe