bug#37337: 2019-08-31; Error when `TeX-fold-hide-item' acts on evaporated overlays

[Florent Rougon]

Dear AUCTeX maintainers,

First of all, thank you very much for your great work on AUCTeX!

I found a problem when trying to fold comments in a .dtx file (which
seems very useful to me given the verbosity of the .dtx format). It
manifests with the following backtrace:

Debugger entered--Lisp error: (wrong-type-argument integer-or-marker-p nil)
  TeX-fold-overfull-p(nil nil "…")
  TeX-fold-hide-item(#<overlay in no buffer>)
  TeX-fold-region-comment(1 356)
  TeX-fold-region(1 356)
  TeX-fold-buffer()
  funcall-interactively(TeX-fold-buffer)
  call-interactively(TeX-fold-buffer nil nil)
  command-execute(TeX-fold-buffer)

and can be reproduced this way:

1. Configure AUCTeX to fold comments:

   (setq TeX-fold-type-list '(comment))

2. Visit a buffer containing the attached 'test.dtx' file.

3. Activate TeX-fold-mode (either with `C-c C-o C-f' or from the menus:
   LaTeX -> Show/Hide -> Fold Mode).

4. Fold everything in the current buffer according to
   `TeX-fold-type-list'. This can be done with `C-c C-o C-b'.
   Alternatively, you can trigger the same bug by selecting a region in
   test.dtx that is large enough to contain 'abc%' and 'def', then do
   `C-c C-o C-r' to fold all configured things in the region.

What happens is that when a comment to be folded consists of only the
percent sign, the overlay created by `TeX-fold-make-overlay' immediately
evaporates because its start and end positions are equal. This causes an
error when `TeX-fold-hide-item' calls `TeX-fold-overfull-p`, which tries
to (goto-char) to the overlay end.

The next email in this bug report will contain a patch ready to apply
using:

  git am some-file

after you have saved that email in mbox format to 'some-file'.

Thanks!

Emacs  : GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.10)
 of 2019-07-22, modified by Debian
Package: 2019-08-31

current state:
==============
(setq
 AUCTeX-date "2019-08-31"
 window-system 'x
 LaTeX-version "2e"
 TeX-style-path '("auctex-style" "auctex-auto" "/home/flo/.local/var/auctex"
                  "/home/flo/lisp/manual-installs/auctex/style"
                  "/home/flo/.emacs.d/auctex/auto"
                  "/home/flo/.emacs.d/auctex/style")
 TeX-auto-save t
 TeX-parse-self t
 TeX-master t
 TeX-command-list '(("TeX"
                     "%(PDF)%(tex) %(file-line-error) %`%(extraopts)
 %S%(PDFout)%(mode)%' %t"
                     TeX-run-TeX nil (plain-tex-mode ams-tex-mode
                                      texinfo-mode)
                     :help "Run plain TeX")
                    ("LaTeX" "%`%l%(mode)%' %T" TeX-run-TeX nil
                     (latex-mode doctex-mode) :help "Run LaTeX")
                    ("Makeinfo" "makeinfo %(extraopts) %t" TeX-run-compile nil
                     (texinfo-mode) :help "Run Makeinfo with Info output")
                    ("Makeinfo HTML" "makeinfo %(extraopts) --html %t"
                     TeX-run-compile nil (texinfo-mode) :help
                     "Run Makeinfo with HTML output")
                    ("AmSTeX" "amstex %(PDFout) %`%(extraopts) %S%(mode)%' %t"
                     TeX-run-TeX nil (ams-tex-mode) :help "Run AMSTeX")
                    ("ConTeXt"
                     "%(cntxcom) --once --texutil %(extraopts) %(execopts)%t"
                     TeX-run-TeX nil (context-mode) :help "Run ConTeXt once")
                    ("ConTeXt Full" "%(cntxcom) %(extraopts) %(execopts)%t"
                     TeX-run-TeX nil (context-mode) :help
                     "Run ConTeXt until completion")
                    ("BibTeX" "bibtex %s" TeX-run-BibTeX nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode context-mode)
                     :help "Run BibTeX")
                    ("Biber" "biber %s" TeX-run-Biber nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Run Biber")
                    ("View" "%V" TeX-run-discard-or-function t t :help
                     "Run Viewer")
                    ("Print" "%p" TeX-run-command t t :help "Print the file")
                    ("Queue" "%q" TeX-run-background nil t :help
                     "View the printer queue" :visible TeX-queue-command)
                    ("File" "%(o?)dvips %d -o %f " TeX-run-dvips t
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Generate PostScript file")
                    ("Dvips" "%(o?)dvips %d -o %f " TeX-run-dvips nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Convert DVI file to PostScript")
                    ("Dvipdfmx" "dvipdfmx %d" TeX-run-dvipdfmx nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Convert DVI file to PDF with dvipdfmx")
                    ("Ps2pdf" "ps2pdf %f" TeX-run-ps2pdf nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Convert PostScript file to PDF")
                    ("Glossaries" "makeglossaries %s" TeX-run-command nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Run makeglossaries to create glossary\n     file")
                    ("Index" "makeindex %s" TeX-run-index nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Run makeindex to create index file")
                    ("upMendex" "upmendex %s" TeX-run-index t
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Run upmendex to create index file")
                    ("Xindy" "texindy %s" TeX-run-command nil
                     (plain-tex-mode latex-mode doctex-mode ams-tex-mode
                      texinfo-mode)
                     :help "Run xindy to create index file")
                    ("Check" "lacheck %s" TeX-run-compile nil (latex-mode)
                     :help "Check LaTeX file for correctness")
                    ("ChkTeX" "chktex -v6 %s" TeX-run-compile nil (latex-mode)
                     :help "Check LaTeX file for common mistakes")
                    ("Spell" "(TeX-ispell-document \"\")" TeX-run-function nil
                     t :help "Spell-check the document")
                    ("Clean" "TeX-clean" TeX-run-function nil t :help
                     "Delete generated intermediate files")
                    ("Clean All" "(TeX-clean t)" TeX-run-function nil t :help
                     "Delete generated intermediate and output files")
                    ("Other" "" TeX-run-command t t :help
                     "Run an arbitrary command")
                    ("Dvips" "dvips %d -o %f" TeX-run-command nil nil)
                    ("View with xdvi" "%v" TeX-run-silent nil nil)
                    ("View with xdvi -paper a4r" "%v -paper a4r"
                     TeX-run-silent
                     nil nil)
                    ("View with the default PostScript viewer" "see %f"
                     TeX-run-discard nil nil)
                    ("View with gv" "gv %f" TeX-run-discard nil nil)
                    ("View with xpdf" "xpdf %s.pdf" TeX-run-silent nil nil)
                    ("View with okular" "okular %s.pdf" TeX-run-silent nil nil))
 )
-- 
Florent

test.dtx
Description: Test file in .dtx format