GNU bug report logs - #73872
30.0.91; emacs-lisp-mode-syntax-table active when calling `describe-variable' on variable with textually large value.

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Sigurd Dam Sonniks <sigurddam <at> hotmail.com>
To: "bug-gnu-emacs <at> gnu.org" <bug-gnu-emacs <at> gnu.org>
Subject: 30.0.91; emacs-lisp-mode-syntax-table active when calling
 `describe-variable' on variable with textually large value.
Date: Fri, 18 Oct 2024 22:14:21 +0000

[Message part 1 (text/plain, inline)]

Hello Emacs folks!

When you call `describle-variable' on a variable with a value that's
large enough that it's moved to the end of the help buffer, the syntax
table is changed to `emacs-lisp-mode-syntax-table' but never changed
back. There is a very easy fix where you just set it back to
`help-mode-syntax-table' at the end of the enclosing
`with-current-buffer', but I guess you could also switch to a
temporary buffer instead. Below is the relevant code snippet with the
first suggested fix applied.

;; If the value is large, move it to the end.
(with-current-buffer standard-output
      (when (> (count-lines (point-min) (point-max)) 10)
            ;; Note that setting the syntax table like below
            ;; makes forward-sexp move over a `'s' at the end
            ;; of a symbol.
            (set-syntax-table emacs-lisp-mode-syntax-table)
            (goto-char val-start-pos)
            (when (looking-at "value is") (replace-match ""))
            (save-excursion
              (insert "\n\nValue:")
      (setq-local help-button-cache (point-marker)))
            (insert "value is shown ")
            (insert-button "below"
                               'action help-button-cache
                               'follow-link t
                               'help-echo "mouse-2, RET: show value")
            (insert ".\n")
    (set-syntax-table help-mode-syntax-table)))


Thank you very much for all your work. I absolutely adore Emacs.

Kind regards,
Sigurd Dam Sonniks

In GNU Emacs 30.0.91 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
version 1.18.2, Xaw3d scroll bars)
Windowing system distributor 'The X.Org Foundation', version 11.0.12101013
System Description: NixOS 24.11 (Vicuna)

Configured using:
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 --disable-build-details --with-modules --with-x-toolkit=lucid
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 (string-bytes 1 761000) (vectors 16 14459)
 (vector-slots 8 178912 15298) (floats 8 32 11) (intervals 56 330 0)
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[Message part 2 (text/html, inline)]

Message #8 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Sigurd Dam Sonniks <sigurddam <at> hotmail.com>,
 Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91;
 emacs-lisp-mode-syntax-table active when calling `describe-variable'
 on variable with textually large value.
Date: Sat, 02 Nov 2024 13:55:15 +0200

> From: Sigurd Dam Sonniks <sigurddam <at> hotmail.com>
> Date: Fri, 18 Oct 2024 22:14:21 +0000
> 
> When you call `describle-variable' on a variable with a value that's
> large enough that it's moved to the end of the help buffer, the syntax
> table is changed to `emacs-lisp-mode-syntax-table' but never changed
> back. There is a very easy fix where you just set it back to
> `help-mode-syntax-table' at the end of the enclosing
> `with-current-buffer', but I guess you could also switch to a
> temporary buffer instead. Below is the relevant code snippet with the
> first suggested fix applied.

Shouldn't the syntax table be left at that value until the buffer is
reused for another variable/function?  Otherwise, why do we set the
syntax table to this value?  Stefan, do you know the reason?

Message #11 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Sigurd Dam Sonniks <sigurddam <at> hotmail.com>, 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91; emacs-lisp-mode-syntax-table active when
 calling `describe-variable' on variable with textually large value.
Date: Thu, 14 Nov 2024 09:40:48 -0500

>> When you call `describle-variable' on a variable with a value that's
>> large enough that it's moved to the end of the help buffer, the syntax
>> table is changed to `emacs-lisp-mode-syntax-table' but never changed
>> back. There is a very easy fix where you just set it back to
>> `help-mode-syntax-table' at the end of the enclosing
>> `with-current-buffer', but I guess you could also switch to a
>> temporary buffer instead. Below is the relevant code snippet with the
>> first suggested fix applied.

I'm curious: in which context did you notice this?
Does it lead to an undesirable behavior in a specific case?

> Shouldn't the syntax table be left at that value until the buffer is
> reused for another variable/function?  Otherwise, why do we set the
> syntax table to this value?  Stefan, do you know the reason?

FWIW, according to my reading of the Git history, this behavior dates
back at least to 2001 when Miles split `help.el` into several files
(I didn't bother to check the previous history of that code on
`help.el`), so it's far from new.

AFAICT the syntax-table of the *Help* buffer shouldn't matter very much
once the buffer is filled: it affects only navigation by the user, where
the prose part would presumably prefer a syntax-table somewhat like that
of `text-mode` whereas the var's value part would prefer something like
that of `elisp-mode`.

But, AFAICT the `help-mode-syntax-table` happens to be a derivative of
`emacs-lisp-mode-syntax-table` just with extra matching of ‘...’, so
reverting to it would be safe enough in most cases.  This said, I think
The Right Thing™ would be to add a `syntax-table` property on the
printed value (regardless if it stays at the beginning or is moved to
the end of the buffer) so it's not affected by the syntax-table used in
the rest of the buffer.


        Stefan

Message #14 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: sigurddam <at> hotmail.com, Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91;
 emacs-lisp-mode-syntax-table active when calling `describe-variable'
 on variable with textually large value.
Date: Sat, 30 Nov 2024 11:49:12 +0200

Ping!  Sigurd, could you please answer Stefan's questions?

> Cc: Sigurd Dam Sonniks <sigurddam <at> hotmail.com>, 73872 <at> debbugs.gnu.org
> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Date: Thu, 14 Nov 2024 09:40:48 -0500
> 
> >> When you call `describle-variable' on a variable with a value that's
> >> large enough that it's moved to the end of the help buffer, the syntax
> >> table is changed to `emacs-lisp-mode-syntax-table' but never changed
> >> back. There is a very easy fix where you just set it back to
> >> `help-mode-syntax-table' at the end of the enclosing
> >> `with-current-buffer', but I guess you could also switch to a
> >> temporary buffer instead. Below is the relevant code snippet with the
> >> first suggested fix applied.
> 
> I'm curious: in which context did you notice this?
> Does it lead to an undesirable behavior in a specific case?
> 
> > Shouldn't the syntax table be left at that value until the buffer is
> > reused for another variable/function?  Otherwise, why do we set the
> > syntax table to this value?  Stefan, do you know the reason?
> 
> FWIW, according to my reading of the Git history, this behavior dates
> back at least to 2001 when Miles split `help.el` into several files
> (I didn't bother to check the previous history of that code on
> `help.el`), so it's far from new.
> 
> AFAICT the syntax-table of the *Help* buffer shouldn't matter very much
> once the buffer is filled: it affects only navigation by the user, where
> the prose part would presumably prefer a syntax-table somewhat like that
> of `text-mode` whereas the var's value part would prefer something like
> that of `elisp-mode`.
> 
> But, AFAICT the `help-mode-syntax-table` happens to be a derivative of
> `emacs-lisp-mode-syntax-table` just with extra matching of ‘...’, so
> reverting to it would be safe enough in most cases.  This said, I think
> The Right Thing™ would be to add a `syntax-table` property on the
> printed value (regardless if it stays at the beginning or is moved to
> the end of the buffer) so it's not affected by the syntax-table used in
> the rest of the buffer.
> 
> 
>         Stefan
> 
> 
> 
> 
> 

Message #17 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: sigurddam <at> hotmail.com, 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91; emacs-lisp-mode-syntax-table active when
 calling `describe-variable' on variable with textually large value.
Date: Sat, 07 Dec 2024 15:10:53 +0200

> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz <at> gnu.org>
> Date: Sun, 01 Dec 2024 18:41:23 -0500
> 
> >> Ping!  Sigurd, could you please answer Stefan's questions?
> > Oh, I am so sorry, Stefan's mail had ended up in my junk folder. I
> > thought we were still waiting for his reply. Thanks for pinging me!
> >> > I'm curious: in which context did you notice this?
> >> > Does it lead to an undesirable behavior in a specific case?
> > I have rainbow-delimiters-mode from the rainbow-delimiters package
> > enabled everywhere, which means that font lock is enabled everywhere.
> > The syntax table of help mode has ?; as a comment starter, so wherever
> > it is used in docstrings, the remainder of that line will be
> > highlighted as a comment in the help buffer. I changed the syntax
> > class of ?; in help-mode-syntax-table, but I noticed that sometimes it
> > would still be interpreted as a comment starter, which led me to
> > finding the bug.
> 
> Aahhhh!
> So the underlying problem already bite in the usual case but you worked
> around it by changing `help-mode-syntax-table`.
> I think your change to `help-mode-syntax-table` is about right, so we
> should include it in any fix to this bug.

I was going to install that change, but then I noticed that it removed
the call to terpri.  Is that intentional?

(And why did we start discussing this in private email, without CC'ing
the bug tracker?  I've now added it; please use Reply All to reply.)

Message #20 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: monnier <at> iro.umontreal.ca, sigurddam <at> hotmail.com
Cc: 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91;
 emacs-lisp-mode-syntax-table active when calling `describe-variable'
 on variable with textually large value.
Date: Sat, 21 Dec 2024 11:12:37 +0200

Ping! Can we please make progress with this bug report?

> Cc: sigurddam <at> hotmail.com, 73872 <at> debbugs.gnu.org
> Date: Sat, 07 Dec 2024 15:10:53 +0200
> From: Eli Zaretskii <eliz <at> gnu.org>
> 
> > From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> > Cc: Eli Zaretskii <eliz <at> gnu.org>
> > Date: Sun, 01 Dec 2024 18:41:23 -0500
> > 
> > >> Ping!  Sigurd, could you please answer Stefan's questions?
> > > Oh, I am so sorry, Stefan's mail had ended up in my junk folder. I
> > > thought we were still waiting for his reply. Thanks for pinging me!
> > >> > I'm curious: in which context did you notice this?
> > >> > Does it lead to an undesirable behavior in a specific case?
> > > I have rainbow-delimiters-mode from the rainbow-delimiters package
> > > enabled everywhere, which means that font lock is enabled everywhere.
> > > The syntax table of help mode has ?; as a comment starter, so wherever
> > > it is used in docstrings, the remainder of that line will be
> > > highlighted as a comment in the help buffer. I changed the syntax
> > > class of ?; in help-mode-syntax-table, but I noticed that sometimes it
> > > would still be interpreted as a comment starter, which led me to
> > > finding the bug.
> > 
> > Aahhhh!
> > So the underlying problem already bite in the usual case but you worked
> > around it by changing `help-mode-syntax-table`.
> > I think your change to `help-mode-syntax-table` is about right, so we
> > should include it in any fix to this bug.
> 
> I was going to install that change, but then I noticed that it removed
> the call to terpri.  Is that intentional?
> 
> (And why did we start discussing this in private email, without CC'ing
> the bug tracker?  I've now added it; please use Reply All to reply.)
> 
> 
> 
> 

Message #23 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: sigurddam <at> hotmail.com, 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91; emacs-lisp-mode-syntax-table active when
 calling `describe-variable' on variable with textually large value.
Date: Sat, 21 Dec 2024 10:10:11 -0500

>> Aahhhh!
>> So the underlying problem already bite in the usual case but you worked
>> around it by changing `help-mode-syntax-table`.
>> I think your change to `help-mode-syntax-table` is about right, so we
>> should include it in any fix to this bug.
> I was going to install that change, but then I noticed that it removed
> the call to terpri.  Is that intentional?

[ I don't think the `terpri` was meant to be removed, no.  ]

Here's the patch I suggest we install (obviously not on `emacs-30`).


        Stefan


2024-12-21  Stefan Monnier  <monnier <at> iro.umontreal.ca>

    * lisp/help-mode.el (help-mode-syntax-table): Mark `;` as punctuation.
    (help-make-xrefs): Use `with-syntax-table`.

    * lisp/help-fns.el (describe-variable): Don't change the buffer's
    syntax-table when moving the var's value to the end (bug#73872).
    Put a `syntax-table` property on the var's value so sexp navigation
    does not depend on the help-mode-syntax-table.


diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index c87c86bae84..ae6b77e7849 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -1437,21 +1437,29 @@ describe-variable
 			     (format-message "`%s'" rep)
 			   rep)))
                       (start (point)))
-		  (if (< (+ (length print-rep) (point) (- line-beg)) 68)
-		      (insert " " print-rep)
-		    (terpri)
-                    (let ((buf (current-buffer)))
-                      (with-temp-buffer
-                        (lisp-data-mode)
-                        (set-syntax-table emacs-lisp-mode-syntax-table)
-                        (insert print-rep)
-                        (pp-buffer)
-                        (font-lock-ensure)
-                        (let ((pp-buffer (current-buffer)))
-                          (with-current-buffer buf
-                            (insert-buffer-substring pp-buffer)))))
-                    ;; Remove trailing newline.
-                    (and (= (char-before) ?\n) (delete-char -1)))
+		 (let (beg)
+		   (if (< (+ (length print-rep) (point) (- line-beg)) 68)
+		       (progn
+		         (setq beg (1+ (point)))
+		         (insert " " print-rep))
+		     (terpri)
+                     (setq beg (point))
+                     (let ((buf (current-buffer)))
+                       (with-temp-buffer
+                         (lisp-data-mode)
+                         (insert print-rep)
+                         (pp-buffer)
+                         (font-lock-ensure)
+                         (let ((pp-buffer (current-buffer)))
+                           (with-current-buffer buf
+                             (insert-buffer-substring pp-buffer))))))
+                   ;; Remove trailing newline.
+                   (and (= (char-before) ?\n) (delete-char -1))
+                   ;; Put a `syntax-table' property on the data, as
+                   ;; a kind of poor man's multi-major-mode support here.
+                   (put-text-property beg (point)
+		                      'syntax-table
+		                      lisp-data-mode-syntax-table))
                   (help-fns--editable-variable start (point)
                                                variable val buffer)
 		  (let* ((sv (get variable 'standard-value))
@@ -1515,10 +1523,6 @@ describe-variable
 	    ;; If the value is large, move it to the end.
 	    (with-current-buffer standard-output
 	      (when (> (count-lines (point-min) (point-max)) 10)
-		;; Note that setting the syntax table like below
-		;; makes forward-sexp move over a `'s' at the end
-		;; of a symbol.
-		(set-syntax-table emacs-lisp-mode-syntax-table)
 		(goto-char val-start-pos)
 		(when (looking-at "value is") (replace-match ""))
 		(save-excursion
diff --git a/lisp/help-mode.el b/lisp/help-mode.el
index 33b8eccab2c..aa705bf56d1 100644
--- a/lisp/help-mode.el
+++ b/lisp/help-mode.el
@@ -143,6 +143,8 @@ help-mode-syntax-table
     ;; break when a quoted string contains punctuation.
     (modify-syntax-entry ?‘ "(’  " table)
     (modify-syntax-entry ?’ ")‘  " table)
+    ;; `;' doesn't start a comment (bug#73872).
+    (modify-syntax-entry ?\; "." table)
     table)
   "Syntax table used in `help-mode'.")
 
@@ -587,13 +587,10 @@
       ;; Skip the first bit, which has already been buttonized.
       (forward-paragraph)
       (let ((old-modified (buffer-modified-p)))
-        (let ((stab (syntax-table))
-              (case-fold-search t)
+        (let ((case-fold-search t)
               (inhibit-read-only t))
-          (set-syntax-table help-mode-syntax-table)
+          (with-syntax-table help-mode-syntax-table
           ;; The following should probably be abstracted out.
-          (unwind-protect
-              (progn
                 ;; Info references
                 (save-excursion
                   (while (re-search-forward help-xref-info-regexp nil t)
@@ -679,7 +676,6 @@
                     (let ((sym (intern-soft (match-string 1))))
                       (if (fboundp sym)
                           (help-xref-button 1 'help-function sym))))))
-            (set-syntax-table stab))
           ;; Delete extraneous newlines at the end of the docstring
           (goto-char (point-max))
           (while (and (not (bobp)) (bolp))

Message #26 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: sigurddam <at> hotmail.com, 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91; emacs-lisp-mode-syntax-table active when
 calling `describe-variable' on variable with textually large value.
Date: Thu, 26 Dec 2024 10:46:37 +0200

> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Cc: sigurddam <at> hotmail.com,  73872 <at> debbugs.gnu.org
> Date: Sat, 21 Dec 2024 10:10:11 -0500
> 
> >> Aahhhh!
> >> So the underlying problem already bite in the usual case but you worked
> >> around it by changing `help-mode-syntax-table`.
> >> I think your change to `help-mode-syntax-table` is about right, so we
> >> should include it in any fix to this bug.
> > I was going to install that change, but then I noticed that it removed
> > the call to terpri.  Is that intentional?
> 
> [ I don't think the `terpri` was meant to be removed, no.  ]
> 
> Here's the patch I suggest we install (obviously not on `emacs-30`).

Thanks.  Sigurd Dam Sonniks, does this patch solve your problem?

Message #29 received at 73872 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: sigurddam <at> hotmail.com, 73872 <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91; emacs-lisp-mode-syntax-table active when
 calling `describe-variable' on variable with textually large value.
Date: Thu, 02 Jan 2025 15:09:18 -0500

>> [ I don't think the `terpri` was meant to be removed, no.  ]
>> Here's the patch I suggest we install (obviously not on `emacs-30`).
> Thanks.  Sigurd Dam Sonniks, does this patch solve your problem?

I pushed it to `master`.


        Stefan

Message #34 received at 73872-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: sigurddam <at> hotmail.com, 73872-done <at> debbugs.gnu.org
Subject: Re: bug#73872: 30.0.91; emacs-lisp-mode-syntax-table active when
 calling `describe-variable' on variable with textually large value.
Date: Sat, 11 Jan 2025 13:16:36 +0200

> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Cc: sigurddam <at> hotmail.com,  73872 <at> debbugs.gnu.org
> Date: Thu, 02 Jan 2025 15:09:18 -0500
> 
> >> [ I don't think the `terpri` was meant to be removed, no.  ]
> >> Here's the patch I suggest we install (obviously not on `emacs-30`).
> > Thanks.  Sigurd Dam Sonniks, does this patch solve your problem?
> 
> I pushed it to `master`.

Thanks.  No further comments, so I'm now closing this bug.

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