Function completion_popup_layer_bindings 

pub fn completion_popup_layer_bindings(
    actions: &ActionIds,
) -> HashMap<BindingMode, KeymapTrie>

Build the completion-popup minor-mode layer’s binding set. Wrapped into the registry by App::push_completion_popup_layer when the popup opens; popped when the popup closes.

Returns one trie keyed under BindingMode::Insert – the only mode the popup is active in. The registry’s merge picks up every entry under that mode whenever the layer is pushed.