Hello LuaTeX developers,

Let me explain an issue I encountered. I'd like to know how to
circumvent it.

In latex tools bundle, there is a file ".tex", which has a file name
with extension only. Its path is
/usr/local/texlive/2022/texmf-dist/tex/latex/tools/.tex
typically.

This example loads that ".tex" successfully:
lualatex --jobname=abcd '\input\relax' '\input' sample2e

Here '\input\relax' actually directs to load ".tex". The console log is:
----------------------------------------------------------------------
This is LuaHBTeX, Version 1.15.0 (TeX Live 2022)
 restricted system commands enabled.
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2022-02-24>
(/usr/local/texlive/2022/texmf-dist/tex/latex/tools/.tex File ignored)
(/usr/local/texlive/2022/texmf-dist/tex/latex/base/sample2e.tex
...
----------------------------------------------------------------------
This is OK.

Next, make a directory "build" for output directory by
mkdir build
. Then this command stalls with the following console output:
lualatex --jobname=abcd --output-directory=build/ '\input\relax' '\input' sample2e
----------------------------------------------------------------------
This is LuaHBTeX, Version 1.15.0 (TeX Live 2022)
 restricted system commands enabled.
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2022-02-24>
! I can't find file `'.
<to be read again>
\let
<*> \input\relax \input
                     sample2e
(Press Enter to retry, or Control-D to exit)
Please type another input file name:
----------------------------------------------------------------------
This affects preview-latex:
https://lists.gnu.org/r/auctex/2022-06/msg00020.html
Is this a supposed behavior of lua(la)tex? If so, is there any
workaround to load ".tex" when both --output-directory and \input are
present?

[Supplementary information with respect to this issue]
(1) pdflatex doesn't have this issue:
pdflatex --jobname=abcd --output-directory=build/ '\input\relax' '\input' sample2e
----------------------------------------------------------------------
This is pdfTeX, Version 3.141592653-2.6-1.40.24 (TeX Live 2022) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2022-02-24>
(/usr/local/texlive/2022/texmf-dist/tex/latex/tools/.tex File ignored)
(/usr/local/texlive/2022/texmf-dist/tex/latex/base/sample2e.tex
...
----------------------------------------------------------------------

(2) In actual usage, "\input\relax" is mandatory because it is an
argument of mylatex.ltx written in temporal xxx.ini file created by
(kinda) script and we are trying to dump format file with -ini like
this:
lualatex -ini --output-directory="build/" -interaction=nonstopmode "&lualatex"
prv_tst-prv.ini "\nonstopmode\nofiles\PassOptionsToPackage{active,tightpage,auctex}{preview}\AtBeginDocument{\ifx\ifPreview\undefined\RequirePackage[displaymath,floats,graphics,textmath,sections,footnotes]{preview}[2004/11/05]\fi}"
 "\input" tst-prv.tex

(3) When I answer the prompt "Please type another input file name:"
providing ".tex", the process continues and completes. However, we can't
take this way because we want to use it like batch operation by
-interaction=nonstopmode option.

(4) When I copy the ".tex" file in the "build" subdirctory, the above
command succeeds:
cp /usr/local/texlive/2022/texmf-dist/tex/latex/tools/.tex build/
lualatex --jobname=abcd --output-directory=build/ '\input\relax' '\input' sample2e
----------------------------------------------------------------------
This is LuaHBTeX, Version 1.15.0 (TeX Live 2022)
 restricted system commands enabled.
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2022-02-24> (./build//.tex File ignored)
(/usr/local/texlive/2022/texmf-dist/tex/latex/base/sample2e.tex
...
----------------------------------------------------------------------
However, such approach isn't suitable for our batch-like usage.

Regards,
Ikumi Keita