On Thu, Jun 16, 2022 at 06:37:27PM -0400, Jeff King wrote:
> > The test and [ commands are used throughout the prompt generation. They
> > also happen to be valid function names that can be defined, leading to
> > unintentional results. Prevent the somewhat unusual case of this
> > happening by simply using [[, which is reserved.
>
> Hmm. I do think we need to be a bit more paranoid about style in the
> prompt and completion code, because they are sourced into the user's
> shell alongside whatever other weird customizations they'd have. So we
> already have adjustments to work under "set -u", and so forth.
>
> But at some point we may say "you have made the environment too hostile
> for us to function". Is redefining "test" to something that doesn't
> behave the same way such a case? Part of me wants to say yes. :)
I'd be inclined to agree! But disregarding a user with malicious
intent, these environment changes can also be unintentional: I came
across it when I stubbed out a quick test() function while prototyping
something unrelated.
> That said, if it's not _hard_ to support, maybe it is worth doing to be
> on the cautious side? A few thoughts:
>
> - my biggest concern on cost is that this is an unusual style for our
> project (which usually writes in POSIX shell, though of course this
> file is meant to be bash/zsh specific). Will it be a maintenance
> burden going forward?
That's possible, but I suspect the burden is minimal. As you said, this
is bash and zsh specific, and for those shell coders who only write
Bourne dialect it's to be read as a "strong" left square bracket. For
example, to minimize any shock to the eyeballs I've intentionally not
re-written string operations `[ a = b ] && [ c = d ]` to `[[ a == b && c
== d ]]`. I promise it wasn't mere laziness!
> - this only changes git-prompt.sh; doesn't the completion code have
> the same issue?
It does. Although there has been some movement towards the
bash-specific builtin:
$ git show v2.36.1:./git-completion.bash | awk '
/(^\[|[^[]\[) |\<test\>/ && !++slb || /\[\[ / && !++dlb || 0;
END { print slb, dlb; }'
119 15
$
This can be addressed in a future patch.
> - I don't write much bash-specific code, but I seem to recall that
> "[[" has some subtle differences to "[". Is it sufficiently a
> superset that these conversions are all equivalent?
>
> I think some like:
>
> > - if [ $pcmode = yes ] && [ $ps1_expanded = yes ]; then
> > + if [[ $pcmode = yes ]] && [[ $ps1_expanded = yes ]]; then
>
> are not equivalent, but it's an actual improvement (bash's builtin
> "[[" isn't confused by unquoted empty variables), but I don't know
> if there may be other gotchas.
>
> (I doubt this is an actual bug in the current code, as $pcmode
> always seems to be set, but just a more defensive style).
Yeah, there's no word splitting or pathname expansion. Also, bash4
onwards changed the < and > operators within [[ to locale order rather
than ASCII.
Regards,
Brad
