With LuaLaTeX (and other engines) it is possible since a few years to set \tracinglostchars=3 (the LaTeX kernel uses 2 not 3).
This means that attempting to use a character not existing in the current document font will cause an error on built. But it seems such errors are not parsed by AUCTeX, and as a result, this important mechanism to not produce wrong output is lost. Here is an example, adapted from https://tex.stackexchange.com/q/739039/293669 ```latex \documentclass{article} \RequirePackage{fontspec}% compile with lualatex \tracinglostchars=3 % 2 is latex default (=warn) \begin{document} Hello.\par \typeout{AAAAAAAAA} \sbox0{\char"3E3A} \typeout{BBBBBBBBB} \char"3E3A\par \typeout{CCCCCCCCC} \end{document} % Local Variables: % TeX-engine: luatex % End: ``` With TeXLive2025 LuaLaTeX you can set \tracinglostchars=5 and the effect is triggered also by the box construction, not only by material ending up on the galley. (the above example is by a contributor to tex.sx who was trying to test that recent TeXLive 2025 LuaLaTeX feature). To reproduce the problem paste the above in an Emacs window, hit C-cC-n to get AUCTeX parse and understand that it is to use LuaLaTeX then hit C-cC-a. No error will be reported. (At least this is what happens at my locale). With XeTeX engine, the error **is** reported by AUCTeX. For info the LuaLaTeX log contains following type of lines. ```text AAAAAAAAA Missing character: There is no 㸺 (U+3E3A) in font [lmroman10-regular]:+tlig;! . \sbox ...box {\color@setgroup #2\color@endgroup } l.7 \sbox0{\char"3E3A} % No problem ?! BBBBBBBBB Missing character: There is no 㸺 (U+3E3A) in font [lmroman10-regular]:+tlig;! . <argument> ...hskip:D \c_zero_dim \fi: \tex_par:D \hook_use:n {para/after}\@... l.9 \char"3E3A\par % Or \usebox0 Missing character: There is no 㸺 (U+3E3A) in font [lmroman10-regular]:+tlig;! . <argument> ...hskip:D \c_zero_dim \fi: \tex_par:D \hook_use:n {para/after}\@... l.9 \char"3E3A\par % Or \usebox0 CCCCCCCCC ``` For the above I set \tracinglostchars=5 because I am using a TeXLive2025 LuaLaTeX (*) with 3 in place of 5 you will get only on error line in the log and it will actually be located there after the CCCCCCCCC. Jean-François B. (*) which at time of writing has problems with math mode, but that is another non-AUCTeX matter. ; I can not include TeX-command-list as it contains private things Emacs : GNU Emacs 28.1 (build 1, x86_64-apple-darwin17.7.0, Carbon Version 158 AppKit 1561.61) of 2022-05-10 Package: 14.0.9 current state: ============== (setq window-system 'mac LaTeX-version "2e" TeX-style-path '("~/.emacs.d/auctex/" "/path/to/.emacs.d/elpa/auctex-14.0.9/style" "/path/to/.emacs.d/auctex/.auto" "/path/to/.emacs.d/auctex/style" ".auto" "style") TeX-auto-save t TeX-parse-self t TeX-master t ) _______________________________________________ bug-auctex mailing list [email protected] https://lists.gnu.org/mailman/listinfo/bug-auctex
