Problem with expl3.sty

[Max Chernoff]

Hi Karl,

> Please provide a recipe to reproduce.
> 
> The only way I see tlmgr invoking fmtutil-user is if --usermode is
> explicitly specified, which I doubt these expert users are doing. (I
> also presume they are not explicitly invoking fmtutil-user.)
> Maybe I'm missing something.
> 
>     with some users who definitely know what they are doing ...

I've managed to accidentally make a user format before by deleting the
system format file:

   $ sudo rm $(kpsewhich --engine=pdftex pdftex.fmt)
   $ pdftex '\end'
   This is pdfTeX, Version 3.141592653-2.6-1.40.25 (TeX Live 2023) (preloaded format=pdftex)
    restricted \write18 enabled.
   
   kpathsea: Running mktexfmt pdftex.fmt
   [...]
   mktexfmt [INFO]: /home/max/.texlive2023/texmf-var/web2c/pdftex/pdftex.fmt installed.
   mktexfmt [INFO]: disabled formats: 17
   mktexfmt [INFO]: successfully rebuilt formats: 1
   mktexfmt [INFO]: not selected formats: 40
   mktexfmt [INFO]: total formats: 58
   mktexfmt [INFO]: 
   *************************************************************
   *                                                           *
   * WARNING: you are switching to fmtutil's per-user formats. *
   *         Please read the following warnings!               *
   *                                                           *
   *************************************************************
   [...]
   mktexfmt [INFO]: exiting with status 0
   entering extended mode
   No pages of output.
   Transcript written on texput.log.
   
It would be pretty hard to do this accidentally. I guess it could happen
if fmtutil-sys crashes on the initial install or if an antivirus
randomly deletes the file. Pretty unlikely though.

(I've also found that LuaTeX will build per-user format files if you
replace the one in the TL binary directory with a newer one built from
source, but there's no way that an ordinary user would ever do that.)

I doubt that any of this is very helpful, but maybe it will give someone
some clues.

Thanks,
-- Max