Joel E. Denny <jdenny <at> ces.clemson.edu> writes:
> Or maybe just a regexp engine test with a character class containing
> operators accidentally in the above order:
>
> AT_SETUP([[Regexp Test: [-=<{()}>!+]]])
>
> I find it rarely pays to play the guessing game of "surely the user will
> never do *this*". Moreover, I'm betting that the user will never guess
> that this bizarre string is actually special to autotest.
Magic line-noise strings don't just affect autotest, but all m4sugar-based
languages, including autoconf itself.
This is not a new limitation - m4_split has had the same limitation of a magic
string for a long time now (in fact, my patch this morning merely modified
m4_split by changing its quote string from 4 to 5 characters, so that the same
string would be used in both and that m4_split is now 1 character safer than it
used to be, rather than inventing a new string and doubling the chance of
arbitrary collision with the user). For that matter, prior to 2.62, m4_split
was even more likely to collide, when its magic strings were `` and '' rather
than 2.62's -=<{ and }>=- (there's even a test I added in the 2.62 testsuite
that intentionally tickles the collision problem with the old strings).
http://git.sv.gnu.org/gitweb/?p=autoconf.git;a=commitdiff;h=10fa310
> At the very
> least, can this new limitation be mentioned in the manual? Or did I miss
> it?
So yes, it would probably be worth adding a blurb in the m4sugar documentation
that these two quote strings are special, and that @&t@ will allow you to use
them in an unbalanced manner if you really need them. Patch to follow when I
get the time. And I'm open to changing the string to something even more
implausible, as long as both m4_split and m4_expand use the same string pairs,
the two strings look reasonably symmetric, and the two strings contain the
appropriate () needed by m4_expand.
On a related note, config.status used to use the special string |#_!!_#| on the
assumption the user would never do that, but our move to awk in 2.62 rendered
that magic string obsolete.
--
Eric Blake
