kakoune/test/hooks/completion-hide/rc

declare-option completions line1
declare-option completions line2
set-option global completers \
	option=line1 \
	option=line2 \

define-command update-completions %{
    set-option global line1 "1.1@%val{timestamp}" foo()||
    set-option global line2 "2.1@%val{timestamp}" foo()||
}

hook global InsertCompletionHide .+ %{
    evaluate-commands -draft %{
        select %val{hook_param}
        execute-keys i<lt><esc>a<gt><esc>
	execute-keys <a-h>i "accepted completion: "
    }
}
hook global InsertCompletionHide '' %{
    evaluate-commands -draft %{
        execute-keys <a-h>i "rejected completion "
    }
}