Subject: Wrong warning position given by the byte compiler for a malformed function

From: Alan Mackenzie <[email-masked]>
Date: Mon, 27 Nov 2023 12:40:49 +0000

Hello, Emacs

In any recent or semi-recent Emacs create a file bad-error-position.el
with these contents:

    (defun foo ()
      (let ((bar 'bar))
        (if ("foo")  ; Erroneous "function".
            (baz))))))

..  Use M-x compile-defun to compile it.  This gives an error message:

    Buffer bad-error-position.el:2:4: Warning: `foo' is a malformed function

..  This position 2:4 is wrong; it is the position of the `let' symbol.
The correct position would be 3:6, the position of the `if' symbol.

#########################################################################

The cause of the error is in byte-optimize-form in
lisp/emacs-lisp/byte-opt.el.  There, although the code recurses, it
fails to push the current form onto byte-compile-form-stack.  Thus when
byte-compile-warn-x is called, there is nothing usable on that stack
inside the let form.

-- 
Alan Mackenzie (Nuremberg, Germany).