feat: single user mode on NVIDIA PCs: SDDM autologin into the Plasma session, without the conversion

lib/backend.sh

@@ -146,8 +146,13 @@ backend_apply() {
         for id in "${want[@]}"; do [[ "$id" == "$c" ]] && WANTED[$c]=1; done
     done
     # The same rules as the menu's toggles.
-    [[ "${WANTED[single]:-0}" == 1 ]] && WANTED[gaming]=1
-    [[ "${WANTED[gaming]:-0}" == 0 ]] && { WANTED[single]=0; WANTED[boot]=0; }
+    # (Single user mode only needs the conversion where it is offered: not on NVIDIA PCs.)
+    [[ "${WANTED[single]:-0}" == 1 ]] && component_available gaming && WANTED[gaming]=1
+    if component_available gaming; then
+        [[ "${WANTED[gaming]:-0}" == 0 ]] && { WANTED[single]=0; WANTED[boot]=0; }
+    else
+        WANTED[boot]=0
+    fi
     [[ "${WANTED[bigpicture]:-0}" == 1 ]] && WANTED[nvidia]=1
     [[ "${WANTED[nvidia]:-0}" == 0 ]] && WANTED[bigpicture]=0
     [[ "${WANTED[poweroff]:-0}" == 1 ]] && WANTED[machine]=1

lib/login-manager.sh

@@ -167,6 +167,20 @@ switch_to_sddm() {
     ok "SDDM is the login manager from the next boot on."
 }
 
+remove_sddm_base_autologin() {
+    # /etc/sddm.conf is read last: an [Autologin] there would override our fragments.
+    if [[ -f /etc/sddm.conf ]] && grep -q '^\[Autologin\]' /etc/sddm.conf; then
+        backup_file /etc/sddm.conf
+        sudo awk '
+            /^\[Autologin\]/ { skip=1; next }
+            /^\[/ { skip=0 }
+            !skip { print }
+        ' /etc/sddm.conf | sudo tee /etc/sddm.conf.tmp > /dev/null &&
+            sudo mv /etc/sddm.conf.tmp /etc/sddm.conf
+        info "Removed [Autologin] from /etc/sddm.conf (backup kept)."
+    fi
+}
+
 configure_sddm_autologin() {
     # User= and Relogin= live in our own fragment; steam-set-session keeps
     # Session= up to date in zz-steamos-autologin.conf, which sorts later
@@ -182,16 +196,7 @@ Session=gamescope-session.desktop
 Relogin=true
 EOF
 
-    if [[ -f /etc/sddm.conf ]] && grep -q '^\[Autologin\]' /etc/sddm.conf; then
-        backup_file /etc/sddm.conf
-        sudo awk '
-            /^\[Autologin\]/ { skip=1; next }
-            /^\[/ { skip=0 }
-            !skip { print }
-        ' /etc/sddm.conf | sudo tee /etc/sddm.conf.tmp > /dev/null &&
-            sudo mv /etc/sddm.conf.tmp /etc/sddm.conf
-        info "Removed [Autologin] from /etc/sddm.conf (backup kept)."
-    fi
+    remove_sddm_base_autologin
 
     # Start in gamescope, through CachyOS's own tool so its file is current.
     sudo /usr/lib/steamos/steam-set-session gamescope-session.desktop

lib/menu.sh

@@ -55,7 +55,7 @@ component_available() {
     case "$1" in
         # gamescope's own session is broken on NVIDIA: the conversion is replaced by "Gaming on NVIDIA" there (shown
         # anyway when it's already on, so it can be turned off).
-        gaming|boot|single|glyphs) ! nvidia_present || gaming_status ;;
+        gaming|boot|glyphs) ! nvidia_present || gaming_status ;;
         nvidia) nvidia_available ;;
         bigpicture) bigpicture_available ;;
         machine|poweroff) machine_available ;;
@@ -230,7 +230,7 @@ defaults_options() {
                 warn "Leaving out ${LABEL[$c]%%:*}: not available on this PC."
             fi
         done
-        [[ "${WANTED[single]}" == 1 ]] && WANTED[gaming]=1
+        [[ "${WANTED[single]}" == 1 ]] && component_available gaming && WANTED[gaming]=1
         for c in "${COMPONENTS[@]}"; do
             [[ "${WANTED[$c]}" == 1 && -n "${PARENT[$c]:-}" ]] && WANTED[${PARENT[$c]}]=1
         done
@@ -274,7 +274,8 @@ toggle_component() {
     component_selectable "$c" || return 1
     WANTED[$c]=$(( 1 - WANTED[$c] ))
     # Single user mode only makes sense on top of the SteamOS conversion.
-    if [[ "$c" == single && "${WANTED[single]}" == 1 ]]; then WANTED[gaming]=1; fi
+    # (On NVIDIA the conversion isn't offered: single user mode logs in by itself, see lib/single-user.sh.)
+    if [[ "$c" == single && "${WANTED[single]}" == 1 ]] && component_available gaming; then WANTED[gaming]=1; fi
     if [[ "$c" == gaming && "${WANTED[gaming]}" == 0 ]]; then WANTED[single]=0; WANTED[boot]=0; fi
     # Where to boot to is part of the conversion, too.
     if [[ "$c" == boot && "${WANTED[boot]}" == 1 ]]; then WANTED[gaming]=1; fi

lib/single-user.sh

@@ -119,7 +119,36 @@ single_launcher_drop() {
     return 0
 }
 
+# Without the SteamOS conversion (NVIDIA PCs: gamescope's session is broken there) nothing logs in by itself, so single user
+# mode does it: SDDM, autologin into the Plasma session. Named to sort after steam-set-session's zz-steamos-autologin.conf,
+# which may still say gamescope from an earlier conversion.
+SINGLE_AUTOLOGIN=${SINGLE_AUTOLOGIN:-/etc/sddm.conf.d/zzz-steamify-autologin.conf}
+
+single_login_needed() { nvidia_present && ! gaming_status; }
+
+single_login_enable() {
+    single_login_needed || return 0
+    switch_to_sddm || return 1
+    info "Logging in to the desktop by itself (SDDM autologin for $TARGET_USER)..."
+    sudo mkdir -p "$(dirname "$SINGLE_AUTOLOGIN")"
+    sudo tee "$SINGLE_AUTOLOGIN" > /dev/null << EOF
+[Autologin]
+User=$TARGET_USER
+Session=plasma.desktop
+Relogin=true
+EOF
+    remove_sddm_base_autologin
+}
+
+single_login_disable() {
+    [[ -f "$SINGLE_AUTOLOGIN" ]] || return 0
+    sudo rm -f "$SINGLE_AUTOLOGIN"
+    # The way back is CachyOS's own login manager, unless the conversion is on (it keeps SDDM).
+    gaming_status || switch_to_plasmalogin
+}
+
 single_enable() {
+    single_login_enable || return 1
     info "Turning off the lock screen, user switching and logging out..."
     stop_plasmashell_for_edit
 
@@ -145,6 +174,7 @@ single_enable() {
 }
 
 single_disable() {
+    single_login_disable
     info "Restoring the lock screen, user switching and logging out..."
     stop_plasmashell_for_edit
     if has_journal single; then