feat(deck): Implement GNOME/Steam session switching

Adapted from ChimeraOS

system_files/deck/gnome/usr/bin/gnome-session-oneshot

@@ -0,0 +1,50 @@
+#!/bin/bash
+
+set -e
+
+die() { echo >&2 "!! $*"; exit 1; }
+
+SENTINEL_FILE="steamos-session-select"
+
+# If we proceed, execute this
+CHAINED_SESSION="/usr/bin/gnome-session"
+# If we decide the sentinel is consumed, execute this command instead and fail
+RESTORE_SESSION=(/usr/bin/steamos-session-select) # No arguments restores the session
+
+# Find or check config sentinel
+function check_sentinel()
+{
+  if [[ -z ${HOME+x} ]]; then
+    echo >&2 "$0: No \$HOME variable!"
+    # Rather than break we'll just launch plasma and hope for the best?
+    return 0
+  fi
+
+  local config_dir="${XDG_CONF_DIR:-"$HOME/.config"}"
+  (
+    cd "$HOME"
+    cd "$config_dir"
+    sentinel_value="$(cat "$SENTINEL_FILE")"
+    if [[ "$sentinel_value" == "wayland" ]]; then
+      echo "/usr/bin/gnome-session"
+    else
+      return 1
+    fi
+    rm "$SENTINEL_FILE"
+
+  ) || return 1 # If we couldn't read the value or it wasn't what we wanted
+
+  # Found value and removed it, we're good to continue
+  return 0
+}
+
+if CONFIGURED_CHAINED_SESSION=$(check_sentinel); then
+  # We found and consumed the oneshot sentinel, proceed to launch plasma
+  echo >&2 "$0: Found and removed sentinel file for one-shot desktop, proceeding to launch"
+  exec "$CONFIGURED_CHAINED_SESSION"
+else
+  echo >&2 "$0: Sentinel value not found, executing session-select to restore session"
+  "${RESTORE_SESSION[@]}" || echo >&2 "$0: !! Failed to restore previous session, executing chained session"
+  # Session restore should've stopped us, if it is broken at least let plasma continue to open
+  exec "$CHAINED_SESSION"
+fi

system_files/deck/gnome/usr/bin/steamos-session-select

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+#! /usr/bin/bash
+
+set -e
+
+die() { echo >&2 "!! $*"; exit 1; }
+
+# File this script will modify, in addition to (potentially) the per-user sentinel file
+CONF_FILE="/etc/sddm.conf.d/zz-steamos-autologin.conf"
+
+SENTINEL_FILE="steamos-session-select"
+
+# For sanity this shipped file must be present, to ensure we're still on a normal-looking steamos setup.
+CHECK_FILE="/etc/sddm.conf.d/steamos.conf"
+
+session="${1:-gamescope}"
+session_type="wayland"
+
+session_launcher="gamescope-session"
+create_sentinel=""
+
+if [[ "$2" == "--sentinel-created" ]]; then
+  SENTINEL_CREATED=1
+  session_type="wayland"
+fi
+
+# Update config sentinel
+if [[ -z $SENTINEL_CREATED ]]; then
+  [[ $EUID == 0 ]] && die "Running $0 as root is not allowed"
+
+  [[ -n ${HOME+x} ]] || die "No \$HOME variable"
+  config_dir="${XDG_CONF_DIR:-"$HOME/.config"}"
+  session_type=$(
+    cd "$HOME"
+    mkdir -p "$config_dir"
+    cd "$config_dir"
+    if [[ -f "steamos-session-type" ]]; then
+      cp steamos-session-type "$SENTINEL_FILE"
+    else
+      echo "wayland" > "$SENTINEL_FILE"
+    fi
+    cat "$SENTINEL_FILE"
+  )
+
+  # clear steam game desktop shortcut clutter
+  DATA_HOME=${XDG_DATA_HOME:-$HOME/.local/share}
+  grep --files-with-matches "Exec=steam steam://rungameid/" ${DATA_HOME}/applications/* | tr '\n' '\0' | xargs -0 -I {} rm {} || true
+
+  # If we were executed as a session user and then re-execute as root below, we don't want to set root's sentinel too
+  export SENTINEL_CREATED=1
+fi
+
+# We use "plasma" as "desktop" to hook up to SteamOS's scripts
+case "$session" in
+  plasma-wayland-persistent)
+    session_launcher="gnome-session"
+  ;;
+  plasma-x11-persistent)
+    session_launcher="gnome-session"
+  ;;
+  desktop|plasma)
+    session_launcher="gnome-session-oneshot"
+    create_sentinel=1
+  ;;
+  gamescope)
+    session_launcher="gamescope-session"
+    create_sentinel=1
+  ;;
+  *)
+    echo >&2 "!! Unrecognized session '$session'"
+    exit 1
+  ;;
+esac
+
+echo "Updated user selected session to $session_launcher"
+
+# Become root
+if [[ $EUID != 0 ]]; then
+  exec pkexec "$(realpath $0)" "$session" --sentinel-created
+  exit 1
+fi
+
+{
+  echo "[Autologin]"
+  echo "Session=$session_launcher"
+} > "$CONF_FILE"
+
+echo "Updated system autologin session to $session_launcher"
+systemctl reset-failed sddm
+systemctl restart sddm
+echo "Restarted SDDM"

system_files/deck/gnome/usr/share/wayland-sessions/gnome-session-oneshot.desktop

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+[Desktop Entry]
+Name=GNOME on Wayland (single time session)
+Comment=This session logs you into GNOME one time
+Exec=/usr/bin/gnome-session-oneshot
+TryExec=/usr/bin/gnome-session-oneshot
+Type=Application
+DesktopNames=GNOME
+X-GDM-SessionRegisters=true