bug#36114: Can't run preview latex after deleting prv files

[Berthold Lorke]

When running preview latex the first time on a document, everything is
fine.
But then when I delete the created folder _region_.prv and the files
_region_.log, prv_test.fmt, prv_test.log and _region_.tex, I can not run
preview latex (say with C-c C-p C-b)  anymore, it gives me the following
error


Running `Preview-LaTeX' on `~/junk/_region_' with ``lualatex  
-interaction=nonstopmode -file-line-error \&prv_test "/AUCTEXINPUT{" 
_region_.tex "}"''
This is LuaTeX, Version 1.07.0 (TeX Live 2018/Arch Linux) 
 restricted system commands enabled.

kpathsea: Running mktexfmt prv_test.fmt
mktexfmt: mktexfmt is using the following fmtutil.cnf files (in precedence 
order):
mktexfmt:   /etc/texmf/web2c/fmtutil.cnf
mktexfmt: mktexfmt is using the following fmtutil.cnf file for writing changes:
mktexfmt:   /home/berber/.texlive/texmf-config/web2c/fmtutil.cnf
mktexfmt [INFO]: writing formats under /home/berber/.texlive/texmf-var/web2c
mktexfmt [INFO]: did not find entry for byfmt=prv_test, skipped
mktexfmt [INFO]: Disabled formats: 6
mktexfmt [INFO]: Not selected formats: 36
mktexfmt [INFO]: Total formats: 42
mktexfmt [INFO]: exiting with status 0
Sorry, I can't find the format `prv_test.fmt'; will try `prv_test.fmt'.

kpathsea: Running mktexfmt prv_test.fmt
mktexfmt: mktexfmt is using the following fmtutil.cnf files (in precedence 
order):
mktexfmt:   /etc/texmf/web2c/fmtutil.cnf
mktexfmt: mktexfmt is using the following fmtutil.cnf file for writing changes:
mktexfmt:   /home/berber/.texlive/texmf-config/web2c/fmtutil.cnf
mktexfmt [INFO]: writing formats under /home/berber/.texlive/texmf-var/web2c
mktexfmt [INFO]: did not find entry for byfmt=prv_test, skipped
mktexfmt [INFO]: Disabled formats: 6
mktexfmt [INFO]: Not selected formats: 36
mktexfmt [INFO]: Total formats: 42
mktexfmt [INFO]: exiting with status 0
I can't find the format file `prv_test.fmt'!

TeX Output exited as expected with code 1 at Mon Jun  3 16:17:28
LaTeX: LaTeX found no preview images


Also see
https://emacs.stackexchange.com/questions/50829/preview-latex-doesnt-work-when-i-delete-the-region-prv-folder

I want it to be as if I never ran preview latex, so that I can run it
again.
There must be some entry in some other file that gets created that I
have to remove.


Emacs  : GNU Emacs 26.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.8)
 of 2019-04-12
Package: 12.1.2

current state:
==============
(setq
 AUCTeX-date "2019-02-08"
 window-system 'x
 LaTeX-version "2e"
 TeX-style-path '("~/.emacs.d/auctex" "/tmp/.emacs.d/elpa/auctex-12.1.2/style"
                  "/tmp/.emacs.d/auctex/auto" "/tmp/.emacs.d/auctex/style"
                  "auto" "style")
 TeX-auto-save nil
 TeX-parse-self nil
 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 t :help
                     "Run BibTeX")
                    ("Biber" "biber %s" TeX-run-Biber nil t :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 t :help
                     "Generate PostScript file")
                    ("Dvips" "%(o?)dvips %d -o %f " TeX-run-dvips nil t :help
                     "Convert DVI file to PostScript")
                    ("Dvipdfmx" "dvipdfmx %d" TeX-run-dvipdfmx nil t :help
                     "Convert DVI file to PDF with dvipdfmx")
                    ("Ps2pdf" "ps2pdf %f" TeX-run-ps2pdf nil t :help
                     "Convert PostScript file to PDF")
                    ("Glossaries" "makeglossaries %s" TeX-run-command nil t
                     :help "Run makeglossaries to create glossary file")
                    ("Index" "makeindex %s" TeX-run-index nil t :help
                     "Run makeindex to create index file")
                    ("upMendex" "upmendex %s" TeX-run-index t t :help
                     "Run upmendex to create index file")
                    ("Xindy" "texindy %s" TeX-run-command nil t :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")
                    )
 )