Re: How can I debug a macro?

[Phillip Lord]

Alan Schmitt <alan.schmitt@polytechnique.org> writes:

> Hello,
>
> I'm trying to track down a bug in `org-babel-comint-with-output' which
> is a macro in org's ob-comint.el. I know how to use edebug, but it does
> not seem to work with macros. I tried to read the info manual to figure
> out how to use it (for instance info:elisp#Instrumenting Macro Calls),
> but I don't understand what I actually need to do to be able to step
> through this code.
>
> Could someone please give me a hand in debugging this macro?


It depends what you want to do. If you use edebug on the macro itself,
you will get step-through debugging on the macro expansion. This can be
useful, although in most cases, I find "M-x pp-macroexpand-last-sexp"
works better (the macrostep package is worth looking as well, cause it's
very cool).

If you want to debug a *usage* of the macro, then the macro itself needs
to declare to edebug how it should be evaled. In most cases this is
quite easy. For `org-babel-comint-with-output' it's slightly tricker
because AFAICT the `meta' argument is not evaluated.

Consider these:

(defmacro temp-m (one &rest body)
  (declare (debug (form body)))
  (let ((a one))
    `(progn ,@body)))

(defun h ()
  (temp-m
   '(1 2 3)
   (message "hello")))

with the "declare" form in temp-m, calling "h" will step through the
code in "h" as you expect. The debug sexp means "first argument is a
form, the rest are body elements which need stepping through".

So, I think evalling:

(def-edebug-spec org-babel-comint-with-output
  (form body))

should do the trick, although probably you want to send a patch in for
org-comint.el (using the declare version) so that it works for everyone.

Phil