Subject: Re: bug#68514: 30.0.50; minibuffer-choose-completion + elisp-c-a-p delete next sexp when completing after open paren

From: Stefan Monnier <[email-masked]>
Date: Wed, 17 Jan 2024 11:37:15 -0500

> If point is already at the start of a sexp (e.g. immediately after an
> open paren) then backward-sexp will not move point and the beginning
> of the completion region would (correctly) be the original point.
>
> forward-sexp, in this case, will move over the next sexp after point
> and include it in the completion region, even if it's a string or
> list.

The fact that it did not move point is not really the problem.
The problem is that point may be just before something like whitespace,
so the

                         (member (char-syntax (char-after beg))
                                 '(?\" ?\())

doesn't notice that `forward-sexp` will actually jump over a list or
some other such uncompletable sexp.

I suggest the patch below instead (which also uses `min` to try to make
sure we don't return a BEG..END which doesn't contain point).

        Stefan

diff --git a/lisp/progmodes/elisp-mode.el b/lisp/progmodes/elisp-mode.el
index 00910fb67c7..60d58191175 100644
--- a/lisp/progmodes/elisp-mode.el
+++ b/lisp/progmodes/elisp-mode.el
@@ -657,12 +657,12 @@ elisp-completion-at-point
 		    (save-excursion
 		      (backward-sexp 1)
 		      (skip-chars-forward "`',‘#")
-		      (point))
+		      (min (point) pos))
 		  (scan-error pos)))
 	   (end
-	    (unless (or (eq beg (point-max))
-			(member (char-syntax (char-after beg))
-                                '(?\" ?\()))
+	    (unless (or (>= beg (point-max))
+		        (not (memq (char-syntax (char-after beg))
+		                   '(?w ?\\ ?_))))
 	      (condition-case nil
 		  (save-excursion
 		    (goto-char beg)