bug#75893: texlive: kpathsea doesn't use ls-R database

[vicvbcun]

Hello Guix!

Consider the following example latex document:
--8<---------------cut here---------------start------------->8---
\documentclass{article}
        \usepackage{mathtools}

\begin{document}
        hello world
\end{document}
--8<---------------cut here---------------end--------------->8---
Compiling it with LuaLaTeX under strace in a shell with 
texlive-scheme-basic, texlive-collection-luatex and 
texlive-collection-latexextra, it seems like most of the time is spent 
recursively searching for input files:
--8<---------------cut here---------------start------------->8---
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 27.70    0.080138           2     30174           getdents64
 21.99    0.063605           4     15455       259 openat
 17.44    0.050460           3     16179        32 newfstatat
 14.37    0.041583           3     10440     10296 access
  8.42    0.024348           1     15196           close
  7.76    0.022456           1     15201           fstat
  0.79    0.002278           1      1868           write
--8<---------------cut here---------------end--------------->8---
and similarly for pdflatex.

As an extreme example, consider
--8<---------------cut here---------------start------------->8---
\documentclass{tudapub}

\begin{document}
        hello world
\end{document}
--8<---------------cut here---------------end--------------->8---
compiled with
--8<---------------cut here---------------start------------->8---
texlive-scheme-basic
texlive-collection-luatex
texlive-collection-latexextra
texlive-roboto texlive-urcls
texlive-xcharter
texlive-tuda-ci
--8<---------------cut here---------------end--------------->8---

This takes over 14 seconds (compared to about 2.7 seconds for lualatex 
from Arch Linux) and from strace:
--8<---------------cut here---------------start------------->8---
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 32.60    5.926537           3   1801518           getdents64
 26.46    4.809462           5    900841       284 openat
 20.90    3.799744           4    896057    895349 access
 10.19    1.851520           2    900557           close
  9.49    1.724891           1    900575           fstat
  0.28    0.050743           2     17680       229 newfstatat
  0.04    0.007077           1      6073           read
--8<---------------cut here---------------end--------------->8---

The cause for this seems to be kpathsea doesn't treat the ls-R database 
as authoritative.  It is opened but kpathsea falls back to recursive 
searching. 

In the package definition for texlive-libkpathsea, texmf.cnf is modified 
such that the TEXMF variable is set without !! in front of 
$TEXMFSYSCONFIG, $TEXMFSYSVAR and $TEXMFDIST. 
If I override $TEXMF via --cnf-line like
--8<---------------cut here---------------start------------->8---
lualatex \
        --cnf-line='TEXMF =
        
{$TEXMFCONFIG,$TEXMFVAR,$TEXMFHOME,!!$TEXMFSYSCONFIG,!!$TEXMFSYSVAR,!!$TEXMFDIST}'
 \
        example.ltx
--8<---------------cut here---------------end--------------->8---
compilation time for the extreme example above falls to about 2.5 
seconds, without excessive searching. 

The comment above the substitution says that the !! construct wouldn't 
work for texlive-build-system or when building profiles.  I don't know 
if it would be possible to work around this but perhaps it could be 
possible to work around this if installed in profile (or environment)?

vicvbcun