adding t alias conditianal completion

[TechDufus]

This PR closes #379

Since aliases are sourced before completions, we can check for the existence of the alias at this point and conditionally load completion for it here.

[akinomyoga]

Do we need this? If the user would like to reflect the completion settings also to the corresponding aliases, the official way is to set progcomp_alias:

shopt -s progcomp_alias

[TechDufus]

I think you're right.. I'm just having this setting clash with complete -D which is why I'm having issues... This can probably just be dropped...

[akinomyoga]

Thank you for your reply. I now see the problem. I guess this should be fixed at the side of Bash or the default completion function of complete -D -F func.

I checked the mailing list of Bash and found a thread [1] where the discussion seemed to have stopped in the middle, and the change did not happen. I also checked the implementation of bash-completion's __load_completion [2] (which is used by bash-completion's default completion), but it doesn't seem to handle the aliases. There is actually a Bash configuration cykerway/complete-alias [3] to handle aliases, and it is suggested to merge it into bash-completion [4], which haven't yet happened actually. On the other hand, progcomp_alias has a higher priority than the default completion of complete -D in ble.sh [5],

• [1] https://lists.gnu.org/archive/html/bug-bash/2019-01/msg00101.html
• [2] bash-completion/bash_completion at bbe2f099 · scop/bash-completion
• [3] cykerway/complete-alias: automagical shell alias completion;
• [4] adding an alias completion helper · Issue #521 · scop/bash-completion
• [5] ble.sh/core-complete.sh at b568ade0 · akinomyoga/ble.sh