Subject: bug#67900: 30.0.50; Emacs Crahes When Executing Command `consult-buffer'

From: Chang Xiaoduan <[email-masked]>
Date: Fri, 05 Jan 2024 15:04:26 +0800

Hello Andrea,

I still doubt the method you suggest to locate the mis-compiled code
here.

Assume we have n functions all compiled with optimization level
2. Executing one of them, which may call the others, triggers a
crash. Now if we make one of the function compiled with optimization
level 1, and the crash can still be reproduced, then can we conclude
that the function is not involved in the crash? I do not think so. Maybe
that function and some other function both trigger the crash.

Now assume we have n functions all compiled with optimization level 1
and no crash. Making one function compiled with optimization level 2 and
the program crashes. I think now it is safe to conclude that this
function is involved in the crash.

The following is what I have done:

1. I mark all `defun' in consult.el with `(declare (speed 1))'. I can
still reproduce the crash.

2. In addition to step 1, I mark all `cl-defun' in consult.el with
`(declare (speed 1))'. I can still reproduce the crash.

3. In addition to step 2, I mark all `defmacro' in consult.el with
`(declare (speed 1))'. I do not know if this works with `defmacro' or
not, I do it anyway. I can still reproduce the crash. However, I notice
one of the `defmacro' is somehow special:

#+begin_src eamcs-lisp
(defmacro consult--define-state (type)
  "Define state function for TYPE."
  (declare (speed 1))
  `(defun ,(intern (format "consult--%s-state" type)) ()
     ,(format "State function for %ss with preview.
The result can be passed as :state argument to `consult--read'." type)
     (consult--state-with-return (,(intern (format "consult--%s-preview" type)))
                                 #',(intern (format "consult--%s-action" type)))))
#+end_src

>From what I know about "macro" in C, this will expand to a function
definition. I assume this is also true in Emacs Lisp, so:

4. In addition to step 3, I add the `declare' form in the macro
definition, and now the code is:

#+begin_src emacs-lisp
(defmacro consult--define-state (type)
  "Define state function for TYPE."
  (declare (speed 1))
  `(defun ,(intern (format "consult--%s-state" type)) ()
     ,(format "State function for %ss with preview.
The result can be passed as :state argument to `consult--read'." type)
     (declare (speed 1))
     (consult--state-with-return (,(intern (format "consult--%s-preview" type)))
                                 #',(intern (format "consult--%s-action" type)))))
#+end_src

Only after step 4, I can not reproduce the crash. If I regress to step
3, then the crash is reproducible. Thus, I think *at least* the function
generated using this macro is involved in the crash. What do you think
about it?

Thank you