When enabling kill-ring-deindent-mode, it would replace spaces with tabs in modes with indent-tabs-mode turned off. It breaks some languages, that do not support tabs for example elm and yaml. I think it is because the temp buffer it creates has indent-tabs-mode turned on by default. In GNU Emacs 30.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.48, cairo version 1.18.2) System Description: NixOS 25.05 (Warbler) Configured using: 'configure --prefix=/nix/store/1z0lbiv6w4kz0vspk3ivanaiwphyjgnn-emacs-pgtk-30.1 --disable-build-details --with-modules --with-pgtk --with-compress-install --with-toolkit-scroll-bars --with-native-compilation --without-imagemagick --with-mailutils --without-small-ja-dic --with-tree-sitter --without-xinput2 --without-xwidgets --with-dbus --with-selinux' Configured features: CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM GTK3 ZLIB Important settings: value of $EMACSLOADPATH: value of $EMACSNATIVELOADPATH: value of $LANG: en_US.UTF-8 locale-coding-system: utf-8-unix Major mode: Nix Minor modes in effect: eat-eshell-visual-command-mode: t eat-eshell-mode: t server-mode: t display-line-numbers-mode: t rainbow-delimiters-mode: t global-auto-revert-mode: t save-place-mode: t winner-mode: t savehist-mode: t global-completion-preview-mode: t completion-preview-mode: t vertico-mode: t marginalia-mode: t corfu-history-mode: t corfu-popupinfo-mode: t global-corfu-mode: t corfu-mode: t yas-global-mode: t yas-minor-mode: t envrc-global-mode: t envrc-mode: t global-treesit-auto-mode: t hexl-follow-ascii: t repeat-mode: t mood-line-mode: t apheleia-mode: t kill-ring-deindent-mode: t global-word-wrap-whitespace-mode: t word-wrap-whitespace-mode: t electric-pair-mode: t which-key-mode: t elpaca-use-package-mode: t override-global-mode: t global-eldoc-mode: t show-paren-mode: t electric-indent-mode: t mouse-wheel-mode: t file-name-shadow-mode: t global-font-lock-mode: t font-lock-mode: t minibuffer-regexp-mode: t line-number-mode: t global-visual-line-mode: t visual-line-mode: t transient-mark-mode: t auto-composition-mode: t auto-encryption-mode: t auto-compression-mode: t Load-path shadows: /nix/store/rmgcpv2qf9pdchjkx0h0r6zrsr06rig9-emacs-packages-deps/share/emacs/site-lisp/site-start hides /nix/store/1z0lbiv6w4kz0vspk3ivanaiwphyjgnn-emacs-pgtk-30.1/share/emacs/site-lisp/site-start /home/jerpo/.config/emacs/elpaca/builds/transient/transient hides /nix/store/1z0lbiv6w4kz0vspk3ivanaiwphyjgnn-emacs-pgtk-30.1/share/emacs/30.1/lisp/transient Features: (shadow sort mail-extr emacsbug message puny rfc822 mml mml-sec epa epg rfc6068 epg-config gnus-util mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils jka-compr helpful cc-langs cc-vars cc-defs trace cl-print edebug info-look info f help-fns radix-tree elisp-refs rfc2104 tramp-cmds tramp-cache time-stamp dumb-jump popup dash s pcmpl-unix dired-aux hl-line dired dired-loaddefs avy misearch multi-isearch tramp-sh yank-media markdown-mode noutline outline mood-line-segment-checker eglot external-completion flymake diff ert ewoc debug backtrace find-func imenu grep xref calc-misc calc-undo calc-alg calc-ext calc-menu calc calc-loaddefs rect calc-macs mule-util face-remap eshell-syntax-highlighting em-unix em-term em-script em-prompt em-pred em-ls em-hist em-glob em-extpipe em-cmpl em-dirs em-basic em-banner em-alias em-tramp eshell esh-mode esh-var eat term/xterm xterm term disp-table ehelp esh-cmd generator esh-ext esh-opt esh-proc esh-io esh-arg esh-module esh-module-loaddefs esh-util apheleia apheleia-rcs apheleia-dp apheleia-formatters apheleia-utils apheleia-log apheleia-formatter-context dabbrev vc-git vc-dispatcher mood-line-segment-vc nix-mode ffap thingatpt smie nix-repl nix-shell nix-store magit-section derived benchmark cursor-sensor llama comp comp-cstr nix-log nix-instantiate nix-shebang nix-format nix vertico-directory comp-run comp-common server display-line-numbers rainbow-delimiters autorevert filenotify saveplace winner savehist completion-preview 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eshell-syntax-highlighting-autoloads eat-autoloads trashed-autoloads dired-subtree-autoloads dired-hacks-utils-autoloads corfu-autoloads cape-autoloads orderless-autoloads marginalia-autoloads vertico-autoloads rainbow-delimiters-autoloads mood-line-autoloads helpful-autoloads f-autoloads elisp-refs-autoloads dash-autoloads s-autoloads avy-autoloads vundo-autoloads no-littering-autoloads base16-stylix-theme base16-theme init go-ts-mode rx c-ts-common treesit indent-aux word-wrap-mode elec-pair edmacro kmacro elpaca-menu-elpa which-key elpaca-menu-melpa elpaca-menu-org cl-extra help-mode elpaca-use-package use-package use-package-ensure use-package-delight use-package-diminish use-package-bind-key bind-key easy-mmode use-package-core elpaca-use-package-autoloads elpaca-log elpaca-ui url url-proxy url-privacy url-expand url-methods url-history url-cookie generate-lisp-file url-domsuf url-util url-parse auth-source eieio eieio-core cl-macs password-cache json subr-x map byte-opt gv bytecomp byte-compile url-vars mailcap cl-seq elpaca elpaca-process elpaca-autoloads cus-edit pp cus-load icons wid-edit cl-loaddefs cl-lib early-init rmc iso-transl tooltip cconv eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel term/pgtk-win pgtk-win term/common-win touch-screen pgtk-dnd tool-bar dnd fontset image regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic indonesian philippine cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european ethiopic indian cyrillic chinese composite emoji-zwj charscript charprop case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs theme-loaddefs faces cus-face macroexp files window text-properties overlay sha1 md5 base64 format env code-pages mule custom widget keymap hashtable-print-readable backquote threads dbusbind inotify dynamic-setting system-font-setting font-render-setting cairo gtk pgtk multi-tty move-toolbar make-network-process native-compile emacs) Memory information: ((conses 16 873047 225658) (symbols 48 41607 1) (strings 32 304075 12621) (string-bytes 1 7953692) (vectors 16 936601) (vector-slots 8 8676661 205873) (floats 8 453 1999) (intervals 56 16329 15127) (buffers 992 56))