Tab completion for snaps

Starting with snapd 2.30, commands and aliases packaged in snaps are able to perform tab-completion in the bash shell, and in the future that same mechanism may be enabled in other shells as well.

For this to work, a completer key must be specified under the application scope in snap.yaml or snapcraft.yaml, pointing to a bash completion snippet (that would in traditional packaging be dropped in /usr/share/bash-completion/completions). With that, snapd will create the necessary system setup to run the completer script confined. The completer must be for the full app name (<snap>.<app>), without considering aliases.

Two sample snaps that implement this are the http and test-snapd-complexion (edge) snaps.

Snapcraft has had support for the completer attribute of snap apps since version 2.33.

Debugging tab completion of a strict snap can be hard, so we wrote a guide for it.

Extending this tab completion mechanism to other shells (zsh for example) is relatively simple. All that is needed is a marshaller of the completion request. See complete.sh in the snapd source for details.

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