Problem with expl3.sty

[Max Chernoff]

Hi Karl,

>     (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 
> 
> I don't understand

I've been testing some changes to LuaTeX by doing something like this:

   $ git clone https://github.com/TeX-Live/luatex/
   $ cd luatex
   [make whatever changes to the source]
   $ ./build.sh --make --parallel
   $ sudo cp build/texk/web2c/luatex /usr/local/texlive/2023/bin/x86_64-linux/luatex
   
Then, when I run:

   $ luatex '\end'
   
I've had all of the following happen:

   1. LuaTeX compiles the file as normal
      
   2. "Fatal format file error; I’m stymied"
      
   3. LuaTeX detects that the format files are old, so it rebuilds the
      format files just like it does if you've deleted them.

No regular user would ever do this, so this unpredictable behaviour is
perfectly fine with me.

Also, if I symlink "luahbtex" to the freshly-built "luatex", then
running "lualatex" will rebuild its format every time that you run it.
Doing this is obviously completely unsupported, so this behaviour isn't
a problem either.

Thanks,
-- Max