Add mutter property check rather only relying on XDG_SESSION_DESKTOP …

[echu2013]

Add support to gnome-shell +v48 on Ubuntu 25.04 and probably others as well

[gemini-code-assist]

Summary of Changes

Hello @echu2013, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the turn-off-monitors script's ability to function correctly in modern Gnome-Shell environments, particularly those utilizing Wayland. By adding a direct check for mutter display configuration properties, the script can now reliably detect and interact with Gnome's display management, ensuring broader compatibility beyond just relying on the XDG_SESSION_DESKTOP variable.

Highlights

• Enhanced Gnome-Shell Compatibility: The script now supports newer Gnome-Shell versions (v48+) on Ubuntu 25.04 and potentially other distributions by checking for mutter property support.
• Improved Wayland Environment Detection: A new check has been introduced to determine if org.gnome.Mutter.DisplayConfig's PowerSaveMode property is available via busctl, providing a more reliable way to identify compatible Gnome Wayland environments.

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[gemini-code-assist]

Code Review

This pull request adds a check for a Mutter D-Bus property to support newer GNOME versions, which is a great addition. However, I found a critical bug in the implementation of the check that will prevent it from working as intended. My review provides a fix for this bug. I've also included some suggestions to improve the code's readability and adherence to shell scripting best practices, such as improving comments and variable naming.

[gemini-code-assist]

There's a critical issue in the busctl command. The object path and interface are being passed as a single argument because of a missing line continuation (\). This will likely cause the check to always fail, preventing the new detection mechanism from working.

I've included a fix in the suggestion below, and also took the opportunity to make a few other improvements for maintainability:

• The comment # C is not descriptive. I've replaced it with one that explains the purpose of the check.
• It's good practice to initialize variables. I've initialized mutter_property_supported to false for clarity and robustness.
• Shell script convention is to use lowercase for script-local variables to avoid conflicts with environment variables. I've renamed MUTTER_PROPERTY_SUPPORTED to mutter_property_supported.

# Check if Mutter's PowerSaveMode property is available (for GNOME 48+).
mutter_property_supported=false
if busctl --user get-property \
    org.gnome.Mutter.DisplayConfig \
    /org/gnome/Mutter/DisplayConfig \
    org.gnome.Mutter.DisplayConfig \
    PowerSaveMode &>/dev/null; then
    mutter_property_supported=true
fi

[echu2013]

I don't get the bot's suggestion, this was previously tested and worked just fine :-)

[gemini-code-assist]

To align with the suggested fix and shell scripting best practices, this variable should be updated to its new lowercase name. This change is necessary for the new GNOME detection logic to function correctly.

    if [[ $XDG_SESSION_DESKTOP == gnome* || $mutter_property_supported ]]; then