Homebrew bash completions not loaded

[quantumfrost]

Additional Info

• I am using Windows Subsystem for Linux

Output of brew config

HOMEBREW_VERSION: 4.4.20
ORIGIN: https://github.com/Homebrew/brew
HEAD: 47ef1a3b0b742a78be35c016df6a0279d6035ebb
Last commit: 13 days ago
Branch: stable
Core tap JSON: 10 Feb 19:39 UTC
HOMEBREW_PREFIX: /home/linuxbrew/.linuxbrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_MAKE_JOBS: 4
Homebrew Ruby: 3.3.7 => /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/3.3.7/bin/ruby
CPU: quad-core 64-bit haswell
Clang: N/A
Git: 2.30.2 => /bin/git
Curl: 7.74.0 => /bin/curl
Kernel: Linux 6.1.0-0.deb11.21-amd64 x86_64 GNU/Linux
OS: Debian GNU/Linux 11 (bullseye) (bullseye)
Host glibc: 2.31
/usr/bin/gcc: 10.2.1
/usr/bin/ruby: N/A
glibc: 2.35_1
gcc@11: N/A
gcc: 14.2.0_1
xorg: N/A

Output of brew doctor

Your system is ready to brew.

Description of issue

Bash completions for brew and other commands installed via brew aren't loaded. /home/linuxbrew/.linuxbrew/etc/profile.d/bash_completion.sh checks for $BASH_COMPLETION_VERSINFO and only proceeds if it's empty. However it's not empty because the system bash completion script (/usr/share/bash-completion/bash_completion) was already run. If I unset that variable in that script, it works fine.

Is this a bug, or should I be doing something different?

[gromgit]

Not a bug. You're trying to load two versions of the same completion code, the system one just gets picked first.

Unsetting BASH_COMPLETION_VERSINFO may move you forward, but because the two codebases are likely of different versions, there may be subtle bugs that eventually crop up. After all, the whole point of the BASH_COMPLETION_VERSINFO test is to ensure that the completion code is only loaded once, so the upstream developers aren't really thinking about what can break if multiple codes are loaded, and of different versions besidfes.

So if you absolutely want to load the Homebrew version instead (you did install it, after all), you should probably uninstall your system completion package instead. If that's not an option (e.g. the system completion package is a dependency of other packages), then you'll have to pre-set that variable before the system completion package is loaded, then un-set it again afterwards. Something like this might work:

echo "BASH_COMPLETION_VERSINFO=dummy" | sudo tee /etc/profile.d/000-apply-completion-hack
echo "unset BASH_COMPLETION_VERSINFO" | sudo tee /etc/profile.d/zzz-unapply-completion-hack

And if your next question is "won't completing system commands break if I uninstall the system completion package, or stop it from loading?", read the last bash-completion FAQ: What is the search order for the completion file of each target command? (Spoiler: it should still work, but read the answer anyway to understand why, and for the necessary knowledge to investigate why it's not working for you even though "@gromgit said it should work".)

[quantumfrost]

Thanks, I had assumed that homebrew's version of bash_completion was modified to only look at homebrew's completion files. I couldn't remove the system package, but changed the loading script's extension to disable it:
mv /etc/profile.d/bash_completion.sh /etc/profile.d/bash_completion.sh.disabled

And now it works fine, including for system commands. However your method is probably better because the file might be recreated by a system package update.