I thought the whole purpose of with-compilation-unit was to defer
warnings about undefined functions (forward references).
ECL does not ever create such warnings. The only warnings it produces is about undefined variables, but those would be actual errors, and not the source of forward definitions -- i.e. for the code to be properly compiled some defvar/defparameter should have been executed before and then the warning would disappear.
In view of this the main questions are:
a. Should I add those style warnings about undefined functions?
b. What other actions should ECL defer until the end and thus become useful w.r.t. with-compilation-unit?
c. How can I help improve the interaction between ASDF and ECL in this respect? A hook into with-compilation-unit? A hook into the signaling of warnings to keep track of them?