D-Bus

Interprocess communication (IPC) system for apps.
Runs as a service.
Two buses:
- System bus: e.g. to notify about hardware connect/disconnect. Its service: systemctl status dbus.
- Session bus: Specific to user sessions, e.g. communication between Gnome components. Its service: systemctl --user status dbus.
dbus-run-session <cmd>: Starts a new session bus and run cmd in that session (to have access to the session dbus for IPC):
- e.g gnome-shell --nested: Start Gnome within an existing session (for dev. & testing) without affecting the primary UI.

Settings

GSettings: System for Gnome apps to manage their settings.
dconf: underlying backend database for GSettings, with parameters stored in key-value format.

Variant type (like C's union and C++'s std::variant) that may contain:
- Simple types: int, bool.
- Complex types: array of dict.
Usage: data to be serialized:
- Data sent over D-Bus.
- Saved settings with GSettings.

Create a new extension: gnome-extension create --interactive

Two mandatory files: metadata.json, and extension.js
extension.js:
- Runs in the same process as gnome-shell.
- Uses Clutter and St toolkits (latter builds on Clutter to provide more Widgets & CSS), like gnome-shell.
prefs.json: Preferences for extension.
- Runs in a separate process from Gnome-shell.
- Uses GTK4 and Adwaita.
- Adwaita: Toolkit that offers widgets to build Gnome apps (extends GTK base widgets).

gi:// is used to load bindings to C libraries (Gtk, St, Clutter...) generated via GObject introspection.
resource:///org/gnome/shell/... is used to load a file embedded in Gnome-shell iteself.

glib-compile-schemas: compiles an xml file (GSettings schema) into a binary file (that defines app settings).
glib-compile-resources: compiles resources listed in an xml file into binary files that can be accessed dynamically at runtime (to avoid issues with file locations and relative paths).