Re: [PATCH 0/2] First steps in making autoconf ensure a POSIX shell

[Eric Blake]

On 11/07/2012 10:18 AM, Eric Blake wrote:

>>>>> I want to be able to assume the make recipes
>>>>> are run by a POSIX shell.

> 
> What we've done in the past is to do a release that probes for the new
> features but does not mandate them, where the probe is quite verbal to
> tell people to report the situation if the probe fails; then the next
> release can actually start relying on the features.  (Remember how we
> did it when we started requiring shell functions, for example).

More to the point, here's what we had for a couple of release while
spying for shell functions (see commit 734abde when we retired the spy,
because we converted it into a mandatory check):

-m4_define([_AS_SHELL_FN_SPY],
-[_AS_DETECT_SUGGESTED([_AS_SHELL_FN_WORK])
-_AS_RUN([_AS_SHELL_FN_WORK]) || {
-  echo No shell found that supports shell functions.
-  echo Please tell address@hidden about your system,
-  echo including any error possibly output before this message.
-  echo This can help us improve future autoconf versions.
-  echo Configuration will now proceed without shell functions.
-}
-])

>  That
> is, autoconf 2.70 must provide the mechanisms for checking for a POSIX
> shell, and even allow clients like automake to use those mechanisms to
> require a POSIX shell, but autoconf itself won't require a POSIX shell
> until 2.71 at the earliest, even though 2.70 is probing for one.

What I'm thinking right now (but don't have the patch ready yet) is that
we will reinstate a spy that loudly warns if autoconf can't find a POSIX
shell, with a request for bug reports, and in parallel add a new macro
(maybe named AS_SHELL_POSIX) that other packages can use to require a
POSIX shell even with autoconf 2.70.  That is, using the new macro would
switch autoconf from spying to requiring POSIX, but packages that aren't
ready to require POSIX can still safely use 2.70, and the spy will help
us know if anyone is really stuck on a non-museum system where it matters.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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