Re: [PATCH] completion: fix incorrect bash/zsh string equality check

[Robert Estelle <robertestelle@gmail.com>]

I considered dropping this patch entirely since this discussion was
going so far off the rails for a single-char fix, but I hate to leave
things hanging…

> When you do not mean pattern matching and want exact matching, even
> if it is guaranteed that the data you pass through the codepath does
> not have pattern to cause the former, hence the distinction between
> [[ x == y ]] and [ x = y ] does not make a difference, that is a
> mere happenstance, and use of [ x = y ] is the correct thing to do
> in such a case.

I think you've misread what's going on here, or might be
misremembering the shell quoting rules (which would surprise me!).

My assertion about their equivalence was syntactic: there's no
happenstance or reliance on codepaths whatsoever.
If you write:
  [[ "$x" == "$y" ]]
then it doesn't matter what x and y contain. They're quoted: it's just
a literal string comparison of their values.
Their values can contain quotes, newlines, spaces, asterisks, emoji,
etc. and none of that gets any special interpretation.

Regardless, since they're functionally equivalent, I've pushed up a
change to do it the other way and will submit that shortly.

Best,
Robert

On Fri, Oct 8, 2021 at 4:09 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Robert Estelle <robertestelle@gmail.com> writes:
>
> > The choice between the two does not affect correctness, it's purely
> > stylistic here. It only would affect correctness for unquoted
> > arguments or extended comparison operators. Those *are* in use
> > elsewhere in this script and force the use of `[[` in those places.
> >
> > Keep in mind also that this is an autocomplete script. Although it's
> > sourced by both bash and zsh, it does not make sense to attempt to
> > make it work for bare POSIX sh.
>
> Nobody is trying to.  It is more for reducing the risk of people
> shooting their foot by cutting and pasting without thinking.
>
> When you do not mean pattern matching and want exact matching, even
> if it is guaranteed that the data you pass through the codepath does
> not have pattern to cause the former, hence the distinction between
> [[ x == y ]] and [ x = y ] does not make a difference, that is a
> mere happenstance, and use of [ x = y ] is the correct thing to do
> in such a case.