bug#60768: 30.0.50; edebug-instrument-function off by one

[Eli Zaretskii]

> From: No Wayman <iarchivedmywholelife@gmail.com>
> Date: Thu, 12 Jan 2023 21:27:06 -0500
> 
> 1. Save the following elisp to /tmp/test.el:
> 
> 
> --8<---------------cut here---------------start------------->8---
> ;; -*- lexical-binding: t; -*-
> 
> ;;;###autoload
> (defun one ()
>   "ONE"
>   (1+ 0))
> 
> (defun two ()
>   "TWO"
>   (1+ (one)))
> 
> (defun three ()
>   "THREE"
>   (1+ (two)))
> 
> (provide 'test)
> --8<---------------cut here---------------end--------------->8---
> 
> 2. Run emacs from the command line with the following:
> 
> emacs -Q --batch -l /tmp/test.el --eval "(progn (require 'edebug) 
> (edebug-instrument-function #'one))"
> 
> Expected output: Edebug: one
> Actual output: Edebug: two
> 
> If you repeat the test with an additional autoload cookie added 
> above function "two", function one is correctly instrumented.
> 
> If you repeat it with an autoload cookie only above function 
> "three", function two is, incorrectly, instrumented.
> 
> My hunch is find-function-search-for-symbol being thrown off 
> somehow.

It's not a real problem, and it has nothing to do with the autoload
cookie, AFAICT.  If you modify edebug.el like below:

diff --git a/lisp/emacs-lisp/edebug.el b/lisp/emacs-lisp/edebug.el
index 2f7d03e..0ac51ad 100644
--- a/lisp/emacs-lisp/edebug.el
+++ b/lisp/emacs-lisp/edebug.el
@@ -518,6 +518,7 @@ edebug-read-top-level-form
         ;; Don't enter Edebug while doing that, in case we're trying to
         ;; instrument things like end-of-defun.
         (edebug-active t))
+    (save-excursion (end-of-defun))
     (end-of-defun)
     (beginning-of-defun)
     (prog1

i.e., add one call to end-of-defun whose result is thrown away, before
the _real_ call to end-of-defun, the problems go away.

The reason seems to be that end-of-defun calls scan-sexps, and the
first call to scan-sexps does something that wasn't done before.

Stefan, any ideas what could that be?  Any hints where to look?