From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [PATCH 2/2] tools: Clear private variables from
 configure --with-opt
Date: Thu, 23 Oct 2014 11:13:26 +0100
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To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Olaf Hering <olaf@aepfle.de>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Wei Liu <wei.liu2@citrix.com>, xen-devel@lists.xen.org
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On Wed, 2014-10-22 at 14:06 +0100, Ian Jackson wrote:
> Olaf Hering writes ("[PATCH 2/2] tools: Clear private variables from configure --with-opt"):
> > Configure will use variables from environment when substituting a
> > private variable if the corresponding --with*-foo option is omited.
> > This happens for seabios_path, ovmf_path and EXTRA_QEMUU_CONFIGURE_ARGS:
> > 
> > git clean -dfx
> > env EXTRA_QEMUU_CONFIGURE_ARGS=XXXXXXXXXXXXXXXX ./configure
> > grep XXXXXXXXXXXXXXXX config/Tools.mk
> > CONFIG_QEMUU_EXTRA_ARGS:= XXXXXXXXXXXXXXXX
> > 
> > The reason is the empty "action-if-not-given" case. Fix the bug by
> > clearing the variables in this case.
> 
> Why on earth is this a problem ?  My answer is `don't do that then'.

Is the patch harmful though? Do you think people are relying on this
behaviour?

The autoconf docs for AC_ARG_WITH don't really say what the default is
if you omit one of the option shell scripts, presumably it is to do
nothing.

https://autotools.io/autoconf/arguments.html talks about AC_ARG_VAR
which is supposed to be used for this sort of thing.

I've not confirmed this but
http://stackoverflow.com/questions/13848154/passing-environment-variables-to-autoconfs-configure suggests that passing something via the env causes config.status --recheck to do the wrong thing, which seems very plausible.

Ian.