Something weird with when-let*/if-let*

[Eric Abrahamsen <eric@ericabrahamsen.net>]

I've seen this in two different contexts now: using the starred versions
of when-let or if-let results in a `invalid-function' error on the first
let-binding, as if something is trying to treat the whole binding form
as a function.

I got one report on EBDB about this function:

(cl-defmethod ebdb-record-uuid ((record ebdb-record))
  (if-let* ((uuid-field (slot-value record 'uuid)))
      (slot-value uuid-field 'uuid)))

Where the error was:

"(invalid-function (uuid-field (slot-value record (quote uuid))))"

(https://github.com/girzel/ebdb/issues/54#issuecomment-335033393)

And Julien Cubizolles just reported to the Gnus list that this code
chunk from nnimap.el:

(when-let* ((result (eval accept-form)))
  (nnimap-change-group group server)
  (nnimap-delete-article article)
  result)

Was producing a similar error:

"Invalid function: (result (eval accept-form))"

Switching to the un-starred version fixed the problem.

I tried this out on the emacs-26 and master branches, and I can't raise
the error. Julien's on master, with the EBDB reporter it was unclear.
The macroexpansion looks fine, of course.

I guess I should just make a bug report...

Eric