A core tenant of Foundry is a pleasurable command-line experience. And one of the most creature-comforts there is tab-completion.
But how you go about doing that is pretty different across every shell. In Flatpak, they use a hidden internal command called “complete” which takes a few arguments and then does magic to figure out what you wanted.
Implementing that when you have one layer of commands is not too difficult even to brute force. But imagine for a second that every command may have sub-commands and it can get much more difficult. Especially if each of those sub-commands have options that must be applied before diving into the next sub-command.
Such is the case with foundry, because I much prefer foundry config switch over foundry config-switch. Particularly because you may have other commands like foundry config list. It feels much more spatially aware to me.
There will be a large number of commands implemented over time, so keeping the code at the call-site rather small is necessary. Even more so when the commands could be getting proxied from another process or awaiting for futures to complete.
With all those requirements in mind, I came up with FoundryCliCommandTree. The tree is built as an n-ary tree using GNode where you register a command vtable with the command parts like ["foundry", "config", "switch"].
At each layer you can have GOptionEntry like you normally use with GLib-based projects but in this case they will end up in a FoundryCliOptions very similar to what GApplicationClass.local_command_line() does.
So now foundry has a builtin “complete” command like Flatpak and works fairly similarly though with the added complexity to support my ideal ergonomics.