Bug#799545:

[Ville Skyttä <ville.skytta@iki.fi>]

The main apt completion seems to be shipped with the apt package, and
apt-get and apt-cache with bash-completion.

In my opinion it would be best to ship all apt related completions
with the apt package an deprecate/remove them from the bash-completion
package. Please feel free to grab the apt-get and apt-cache
completions from https://github.com/scop/bash-completion and let me
know if/when you do, and I'll remove them from upstream
bash-completion.

There's also completion for apt-build shipped with bash-completion, BTW.