reuse one command's completion for an alias

[arkarkark]

I hope this is the right place to ask, I thought filing an issue wasn't the correct place.

I have an alias for rsync called rs that adds a few command line arguments but I'd also like completion to work. I used to be able to do this with the _rsync function from bash-completion 1.3_3 (from brew) but it fails with v2.18.0

# complete -p rsync
complete -o nospace -F _comp_cmd_rsync rsync
# complete -p rs
complete -o nospace -F _comp_cmd_rsync rs
# rsync --h
--hard-links      --help            --human-readable
# rs --h

I hit tab after the rsync --h and get the suggestions, but when I do it with the last line I don't get any suggestions at all. At least file completion works for rs so thats good.

I'm running GNU bash, version 5.3.20(1)-release (aarch64-apple-darwin25.6.0)

[kgeminicdev]

_comp_cmd_rsync gets the option list by running the command it was called for: "$1" --help in completions-core/rsync.bash. With complete -F _comp_cmd_rsync rs, $1 is rs, and an alias isn't expanded there, so the help call returns nothing and you get no options. The fallback _comp_compgen_usage has the same problem, since it runs comp_args[0], which is also rs. File completion still works because that path doesn't run the command.

Wrap it and pass rsync as the command name:

_comp_cmd_rs() {
    declare -F _comp_cmd_rsync >/dev/null || _comp_load rsync
    _comp_cmd_rsync rsync "${@:2}"
}
complete -o nospace -F _comp_cmd_rs rs

Put this after bash-completion is loaded. _comp_load (2.12+) loads the rsync completion if it hasn't been lazy-loaded yet. The remote host:path completion also checks the version with "$1" --version, so it is fixed by the same wrapper.

[arkarkark]

This is great, thanks so much for your help!

[akinomyoga]

There has also been a PR to add a utility _complete_alias in #104, though the implementation is out of date, and it probably needs adjustments for the current codebase.