`Gio.Settings`: Type inference fails for detailed `changed::*` signals with arbitrary schema keys

[LumenGNU]

Description

The changed signal in Gio.Settings is a detailed signal (GObject terminology) that notifies about changes to schema keys accessed via get_*(key) methods.

According to GLib documentation:

This signal supports detailed connections. You can connect to the detailed signal changed::x in order to only receive callbacks when key x changes.

The signal handler always has the same signature regardless of the key name:

(gsettings: Gio.Settings, key: string) => void

Current Expected

The current Settings.SignalSignatures typing includes only predefined detailed signals that match GSettings object properties (not schema keys):

interface SignalSignatures {
    changed: (arg0: string) => void;
    'changed::backend': (arg0: string) => void;
    'changed::delay-apply': (arg0: string) => void;
    'changed::path': (arg0: string) => void;
    'changed::schema-id': (arg0: string) => void;
    // ...
}

Why it's confusing:

• backend, delay-apply, path, schema-id are GSettings object properties, not typical schema keys
• It creates false impression that only these specific keys are supported for detailed signals
• It suggests these property names are expected to be used as schema keys (which would be confusing in practice)
• The pattern implies a closed set, while changed::* works with any schema key

Problem:

When connecting to changed::${arbitrary_schema_key}, TypeScript cannot infer callback parameter types:

// Type inference fails - parameters have type 'any'
gsettings.connect('changed::my-key', (settings, key) => {
    // settings: any
    // key: any
});

// Must annotate types manually
gsettings.connect('changed::my-key', (settings: Gio.Settings, key: string) => {
    // settings: Gio.Settings
    // key: string
});

Expected Behavior

Type inference should work for any changed::* detailed signal, since:

• All detailed signals have the same handler signature
• The pattern changed::${key} is the standard way to use GSettings API
• Actual schema keys (e.g., criteria, gtk-cursor-blink, custom keys) are far more common than keys named after GSettings properties

Proposed Solution

If TypeScript supports template literal types in this context:

interface SignalSignatures {
    changed: (arg0: string) => void;
    [key: `changed::${string}`]: (arg0: string) => void;
}

Or at minimum, document the current limitation and remove the misleading predefined changed::backend, etc. variants.

References

Gio C API reference: https://docs.gtk.org/gio/signal.Settings.changed.html

Environment:

• GJS Version: 1.80.2 (GNOME 46)
• Girs packages: @girs/gio-2.0@2.86.0-4.0.0-beta.38
• TypeScript: 5.8.3

Additional Context

• This affects all GSettings usage where developers connect to specific schema keys
• Current workaround: manual type annotations for every callback