Emacs 30.0.93 (and maybe earlier versions of Emacs 30) initialize major-mode-remap-defaults with mappings from the built-in modes to the AUCTeX modes:
See lisp/textmodes/tex-mode.el around line 1041 (Or, brace yourself, click that link to GitHub: https://github.com/emacs-mirror/emacs/blob/68bcabf58afddb377d172857ce7648ad3ff09618/lisp/textmodes/tex-mode.el#L1041-L1045 ) AUCTeX does the opposite. This means that after loading AUXTeX, we'll get this "funny" value for major-mode-remap-defaults: ((doctex-mode . docTeX-mode) (latex-mode . LaTeX-mode) (texinfo-mode . Texinfo-mode) (plain-tex-mode . plain-TeX-mode) (tex-mode . TeX-tex-mode) (LaTeX-mode . latex-mode) (plain-TeX-mode . plain-tex-mode) (TeX-mode . tex-mode)) Now this is full chaos. If you set latex-mode in auto-mode-alist, you'll get LaTeX-mode, and the other way around. (I mean, at least Emacs stops after one remapping and doesn't enter infinite loop.) I think AUCTeX should just remove the built-in mappings, which are intended for the case where AUCTeX is not installed. Note that even AUCTeX adds LaTeX-mode entries to auto-mode-alist that will now be redirected to latex-mode. Best, Tim PS: I haven't subscribed to the list, please reply to my address directly if you want to keep me in the loop.
