Re: Autoconf 2.52 is released

[Ralf Corsepius]

Paul Eggert wrote:
> 
> > From: Lars Hecking <address@hidden>
> > Date: Tue, 24 Jul 2001 19:36:00 +0100
> >
> >  Some hints on how to have configure.in compatible with both versions
> >  would be more than welcome.
> 
> The most important bit of advice is to stick only to 2.13-style
> features, and to avoid 2.13's bugs.  (That last bit is the part I
> found the most difficult.  :-)

Fully agreed, but ...

... IMHO, once a configure.in has reached this state, there are
hardly any benefits in using autoconf-2.5x :-)

> One of my biggest problems was the {host,target,build}_alias mess of
> Autoconf 2.13. 

For me, it is subdir handling in autoconf-2.5x. A further problem is
some of the new autoconf-features apparently being immature and
autoconf-2.5x (in most cases actually m4 or sh) issuing cryptical
error messages with encountering actual problems.

> >  One problem now is that 2.5x creates configure from old, 2.1x style
> >  configure.in without errors, implying that they work, while in fact
> >  they don't.
> 
> That's a bit too strong, as it worked for me. 

Hmm, I share Lars H.'s experience, because I also have seen
autoconf-2.5x silently swallow autoconf-2.13 configure.ins without
any complaint, while actually breaking them.

> It depends on the
> configure.in file.  The question is whether it's relatively easy to
> write configure.in files that work with both 2.1x and 2.5x.

AFAICT, keeping configure.ins compatible with 2.13 and 2.5x is
possible and also is not too difficult.

However, IMHO, the actual problem is detecting the spots where
autoconf-2.5x breaks things or reveals problems with existing
configurations (I found  subdir-handling, config.caches,
canonicalization and m4-quoting to be critical), because, though in
many cases autoconf-2.13 configure.ins work or break visibly with
autoconf-2.5x, a not-neglectable minority break silently, which is
rather hard to recognize at all.

Ralf