Dropping support for old bash versions

[scop]

I'd like to look into dropping support for old bash versions soon after we get 2.17.0 out.

Ref: https://github.com/scop/bash-completion/wiki/Minimum-bash-versions

To me it currently looks like as if dropping bash < 5.1 support would be the way to go. The only family of distros in "non-extended maintenance mode" affected by this would be RHEL 8 and friends as far as I can tell. I think those and the ones in extended maintenance are adequately served by current bash completion versions.

Per semver this would come with a bash-completion major version bump.

What this would entail would be code cleanups we can do within the new supported version range, and adjusting CI etc for testing only with those versions.

Yays/nays?

[akinomyoga]

dropping bash < 5.1

What kind of code cleanups can we expect by lifting the version requirement specifically to 5.1? The wiki page lists cleanups for 4.3 and 4.4, but it doesn't list possible cleanups for 5.0 and 5.1. If there are no significant cleanups with 5.0 and 5.1, we can still support 4.4 with essentially the same codebase for 5.1.

Also, in my experience with my repositories, there are still people using Ubuntu 16.04 LTS (in larger systems that are harder to replace).

[akinomyoga]

Like the wiki page says, cleanups for 5.0 and 5.1 (note BTW that I'm not proposing dropping 5.1) are TBD.

Does that mean that you don't have a plan to fill those TBD soon? I wanted to check the contents of the cleanup for 5.0 and 5.1 before deciding on my standpoint about the version requirement, 4.4 or 5.1 (or another option is to keep 4.2 for now; I don't see significant cleanups other than 4.2 nounset bug for "${arr[@]}").

(note BTW that I'm not proposing dropping 5.1)

If I understand it correctly, the items on the wiki page describe the cleanups after we require the features of that version to be available, but not the cleanups after we drop the support of that version. For example, ${foo@Q} can be used when the 4.4 features are assumed, but not when the support for 4.4 is dropped. Then, if we drop Bash < 5.1, I expected that we can apply cleanups for 5.0 and 5.1 as well.

[scop]

I don't have specific plans to fill the TBD's, but will get to them eventually unless someone beats me to it.

I've probably read your earlier comment carelessly initially, but yes you got it right. Might make sense to move the list of LTS OS versions to the section of their bash rather than the following one to make it a bit less confusing.

[scop]

Thanks for filling some info on the Wiki page! I've added and clarified some more.

For a bit of a brain dump, regarding LTS OS versions:

• supporting bash 4.2 is no longer necessary/useful per any LTS OS versions
• supporting bash 4.3 is borderline useful until next June (RHEL/CentOS 7 ELS), but then again to me existing bash-completion versions serve these adequately and we don't need to continue supporting them going forward
• supporting bash 4.4 is moot -- if we've dropped support for 4.3, we've already dropped support for longer living LTS OS versions (RHEL/CentOS 7 ELS, 2026-06-30) than the longest living one with 4.4 (Ubuntu 16.04 ESM, 2026-04-02), and as above, I think existing bash-completion versions serve these just fine
• regarding 5.0 there are some LTS versions that have quite a bit of lifetime left

So taking a conservative route, I think we could draw a line so that bash 5.0 would be the oldest supported version.

With a little more aggressive approach, we could make 5.2 the oldest supported version. This is based on the thoughts that LTS OS versions are not likely to upgrade their packaged bash-completion anyway, the latest of each LTS "family" of OS's has 5.2 these days, and users of earlier than latest of their LTS family may be well enough served by existing bash-completion versions, supported by their distro. So we as the upstream project would continue to serve users on the latest LTS version of their distro, if they want to use something newer than what's offered by it.

My LTS OS thinking is solely based on Linux distros. I don't know, but I assume macOS users we serve will be running a recent bash version through homebrew anyway or can easily upgrade to one. The version shipped with the OS got stuck at 3.x. It's been a long time since I've used any BSD's, so no idea about them really.

Now, there might be other considerations besides LTS OS's regarding what we want to support, but I think they serve fine as guidelines.

[scop]

Re #1530 (review), an example why I think it's important to get this settled up to whatever we want to go with:

If we drop support for bash 4.2, our centos7 test container becomes obsolete. We could replace that with let's say almalinux8 based one which would likely be a relatively "small" change and would get us bash 4.4 test coverage support which we currently don't have.

But if we're actually going to drop support for bash < 5.0, making that almalinux8 container happen is throwaway work, we'd be better off looking further. In that case an almalinux9 based one could be a sane replacement for centos7 to get bash 5.1 test coverage support which we currently lack. ubuntu14 could in that case go as well, and we could replace it with e.g. a ubuntu:24.04 based one to get bash 5.2 test coverage support we currently don't have.

[scop]

AlmaLinux 9 image cooking in #1579