Bash completion does not support bash versions older than 4.4

[sirosen]

I maintain a CLI tool built on click and just had a user report issues with completion on bash 4.2 on a CentOS box.

It seems that nosort was added as an option in bash 4.4. There's even a comment in the completer source about this.
I think it would make sense for the completer to check for BASH_VERSION showing a value below 4.4 and not use nosort in that case. If BASH_VERSION is not set, it's probably safe to assume that nosort is permissible -- I'd rather not degrade environments with a modern bash version but which (for whatever reason) are not showing that env var.

I'm okay with click closing this as a wontfix (old version, not supported), but I want to document the issue and discuss the workaround. If I were to work out the necessary code for this, would there be an appetite for reviewing and merging it?

[davidism]

That's explicitly checked for, but only in order to show an error about the lack of support: https://github.com/pallets/click/blob/main/src/click/shell_completion.py#L302

This was a deliberate decision to drop older versions of Bash. Since the completion system is extensible now, if there is a need to support completion for other shells or versions, an extension can provide that. https://click.palletsprojects.com/en/8.0.x/shell-completion/#adding-support-for-a-shell

[sirosen]

Okay, makes sense. Thanks for the explanation!

At some point in the past, we had custom completion because of some issue (don't recall what) with the builtin completer. I think we're still not loading up completion in a normal way, so we're accidentally bypassing that check.