Re: [1003.1(2016/18)/Issue7+TC2 0001558]: require [^...] in addition to [!...] for bracket expression negation

Reporting a bug on behalf of mirabilos:

On Thu, Feb 17, 2022 at 11:46:52PM +0000, Austin Group Bug Tracker via austin-group-l at The Open Group wrote:
> https://www.austingroupbugs.net/view.php?id=1558 
...
> Summary:                    require [^...] in addition to [!...] for bracket
> expression negation
> ====================================================================== 
> 
> ---------------------------------------------------------------------- 
>  (0005677) mirabilos (reporter) - 2022-02-17 23:46
>  https://www.austingroupbugs.net/view.php?id=1558#c5677 
> ---------------------------------------------------------------------- 
> It gets worse.
> 
> Expecting my objection here to be ignored, I’ve added debugging code to
> mksh (and, indeed, adding the caret needs changes in more than one
> codepath, and it’s very much something I’d like to not need to do
> because more checks make the code slower), and it triggers a warning on:
> 
> […]
> # Sed expression to map a string onto a valid CPP name.
> as_tr_cpp="eval sed
> 'y%*$as_cr_letters%P$as_cr_LETTERS%;s%[^_$as_cr_alnum]%_%g'"
> […]
> echo moo | $as_tr_cpp
> 
> This is what GNU autoconf does by default.
> 
> W: configure[557]: unescaped [^...] in shellglob; this may change the
> meaning in the future!
> 
> So, well, why? Because the variable contains…
> 
> typeset as_tr_cpp='eval sed
> '\''y%*abcdefghijklmnopqrstuvwxyz%PABCDEFGHIJKLMNOPQRSTUVWXYZ%;s%[^_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789]%_%g'\'
> 
> (via “typeset -p”), and without -o noglob, using it as simply
> $as_tr_cpp does, in fact, glob on it.
> 
> Yes, clearly a bug in GNU autoconf… which I’m not personally going to
> even try and report. The …[^… is passed to sed. But it is also
> processed by the shell first, by accident. (This is from
> OpenSSH-portable’s configure.)

So we need to patch autoconf to properly shell-quote the sed script
stored in as_tr_cpp.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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