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

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

[Sigurd Dam Sonniks]

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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:
 'configure
 --prefix=/nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91
 --disable-build-details --with-modules --with-x-toolkit=lucid
 --with-cairo --with-xft --with-compress-install
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 --without-imagemagick --with-mailutils --without-small-ja-dic
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 --with-selinux'

Configured features:
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LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
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TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XAW3D XDBE XIM XINPUT2 XPM
LUCID ZLIB

Important settings:
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  value of $EMACSNATIVELOADPATH: /nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/native-lisp:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
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  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
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  transient-mark-mode: t
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Load-path shadows:
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/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/jsonrpc-1.0.25/jsonrpc hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/jsonrpc
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/transient-20240819.1250/transient hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/transient
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/eglot-1.17/eglot hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/progmodes/eglot
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/project-0.11.1/project hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/progmodes/project
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/xref-1.7.0/xref hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/progmodes/xref
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/flymake-1.3.7/flymake hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/progmodes/flymake
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/compat-30.0.0.0/compat hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/emacs-lisp/compat
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/seq-2.24/seq hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/emacs-lisp/seq
/nix/store/ml4x8pxvz40klw1yabgbjrrpjxlgbbb0-emacs-packages-deps/share/emacs/site-lisp/elpa/eldoc-1.15.0/eldoc hides /nix/store/6qc388fy8gl95smi8q0az92d558nkp4k-emacs-30.0.91/share/emacs/30.0.91/lisp/emacs-lisp/eldoc

Features:
(mailalias rmail auth-source cl-seq eieio eieio-core cl-macs icons json
map byte-opt gv bytecomp byte-compile thingatpt help-fns radix-tree
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Memory information:
((conses 16 83734 22304) (symbols 48 7341 9) (strings 32 24215 2414)
 (string-bytes 1 761000) (vectors 16 14459)
 (vector-slots 8 178912 15298) (floats 8 32 11) (intervals 56 330 0)
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bug#73872: 30.0.91; emacs-lisp-mode-syntax-table active when calling `describe-variable' on variable with textually large value.

[Eli Zaretskii]

> From: Sigurd Dam Sonniks <sigurddam@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?

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

[Eli Zaretskii]

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

> Cc: Sigurd Dam Sonniks <sigurddam@hotmail.com>, 73872@debbugs.gnu.org
> From: Stefan Monnier <monnier@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
> 
> 
> 
> 
> 

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

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@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.)