bug#42016: 26.3; In latex-mode, fill-paragraph changes code to comments

bug#42016: 26.3; In latex-mode, fill-paragraph changes code to comments

[Nate Eldredge]

In latex-mode, using fill-paragraph (M-q) on a non-comment line
following a comment will sometimes merge the non-comment line into the
comment, thus messing up the code.

To reproduce, try opening the following file (with C-x f):

----- snip -----
%% Demonstrate fill bug with GNU emacs
%% Open this file in latex-mode.  Position point on the "yyy" line and hit M-q.
\documentclass{article}
\begin{document}
\begin{environment}
  %% xxx
  yyy
\end{environment}
\end{document}
----- snip ------

Select latex-mode if necessary, position point on the 'yyy' line, and
hit M-q.  The result is

\begin{environment}
  %% xxx yyy
\end{environment}

so that the "live" code 'yyy' has unintentionally been commented out.
This is bad, as M-q should not change the semantics of the file.


In GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu)
 of 2020-03-26, modified by Debian built on lcy01-amd64-020
System Description:	Ubuntu 20.04 LTS

Recent messages:
Loading /etc/emacs/site-start.d/00debian.el (source)...done
Loading /etc/emacs/site-start.d/50autoconf.el (source)...done
For information about GNU Emacs and the GNU system, type C-h C-a.
Undo!

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --enable-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/site-lisp:/usr/share/emacs/site-lisp
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 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
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THREADS LIBSYSTEMD LCMS2

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: LaTeX

Minor modes in effect:
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Memory information:
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bug#42016: 26.3; In latex-mode, fill-paragraph changes code to comments

[Mattias Engdegård]

Thank you! This bug has been fixed in Emacs 27; see https://debbugs.gnu.org/cgi/bugreport.cgi?bug=38152 .

bug#42016: 26.3; In latex-mode, fill-paragraph changes code to comments

[Nate Eldredge]

[-- Attachment #1: Type: text/plain, Size: 769 bytes --]

On Tue, 23 Jun 2020, Mattias Engdegård wrote:

> Thank you! This bug has been fixed in Emacs 27; see https://debbugs.gnu.org/cgi/bugreport.cgi?bug=38152 .

Thanks for the pointer.  I confirm that the patch in bug #38152 fixes the 
previous test case.  However the following slightly different test case 
still has a similar problem:

---- snip ----
\documentclass{article}
\begin{document}
\begin{environment}
   Some code % a comment
   More code
\end{environment}
\end{document}
---- snip ----

If you position point at the start of the line "  More code" and hit M-q, 
the result is

\begin{environment}
   Some code % a comment More code
\end{environment}

Should this bug #42016 be reopened or should I file a new bug?

-- 
Nate Eldredge
nate@thatsmathematics.com

bug#42016: 26.3; In latex-mode, fill-paragraph changes code to comments

[Mattias Engdegård]

reopen 42016
done

23 juni 2020 kl. 17.49 skrev Nate Eldredge <nate@thatsmathematics.com>:

> Thanks for the pointer.  I confirm that the patch in bug #38152 fixes the previous test case.  However the following slightly different test case still has a similar problem:

Oh dear, you are perfectly right. Sorry about my closing the bug prematurely!

> Should this bug #42016 be reopened or should I file a new bug?

Let's try reopening this one first.