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bug#54119: 29.0.50; Edebug: Jumping commands in recursive definitions
From: |
Michael Heerdegen |
Subject: |
bug#54119: 29.0.50; Edebug: Jumping commands in recursive definitions |
Date: |
Fri, 25 Feb 2022 04:36:47 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) |
Michael Heerdegen <michael_heerdegen@web.de> writes:
> #+begin_src emacs-lisp
> (defun my-factorial (n) (if (< n 2) 1 (* n (my-factorial (1- n)))))
> #+end_src
We could exploit the fact that the function is already instrumented.
Every function call of the definition is then wrapped in an
`edebug-after' call:
#+begin_src emacs-lisp
(symbol-function 'my-factorial) ==>
(closure (t) (n)
(edebug-enter 'my-factorial
(list n)
#'(lambda nil
(edebug-after
(edebug-before 0)
12
(if
(edebug-after
(edebug-before 1)
3
(<
(edebug-after 0 2 n)
2))
1
(edebug-after
(edebug-before 4)
11 (* etc...)))))))
#+end_src
We could solve this bug if we temporarily change the function binding of
`edebug-after'. This is a bit tricky, though, mainly because it's not
trivial to restore the original setup:
- two places must be updated: (symbol-function 'edebug-after) and the
entry in `edebug-behavior-alist'
- `edebug-forward-sexp' terminates immediately, it's on the "meta
level", undoing the change in that function is too early, since we
must expect recursive calls of `edebug-after'.
- the actual code is evaluated as an argument of `edebug-after', so the
replacement can also not restore the original function binding
Which means: either we also redefine `edebug-before', or we use
something very different. Here is a proof of concept using
`post-command-hook' for restoring:
#+begin_src emacs-lisp
(defun my-edebug-forward-sexp--around-ad (f &rest args)
(cl-macrolet ((after-fun ()
'(nth 2 (cdr (assq 'edebug edebug-behavior-alist)))))
(let ((orig-after-fun (after-fun)))
(cl-labels ((set-after-fun (f)
(setf (symbol-function 'edebug-after)
(setf (after-fun) f)))
(reset-after-fun ()
(remove-hook 'post-command-hook #'reset-after-fun)
(set-after-fun orig-after-fun)))
(set-after-fun #'edebug-fast-after)
(add-hook 'post-command-hook #'reset-after-fun)
(apply f args)))))
(advice-add 'edebug-forward-sexp :around #'my-edebug-forward-sexp--around-ad)
(advice-add 'edebug-step-out :around #'my-edebug-forward-sexp--around-ad)
#+end_src
Seems to do the job. A patch would not need an advice of course.
Better ideas welcome.
Michael.