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Re: Bug #593838: AX_CFLAGS_GCC_OPTION misuses AS_VAR_PUSHDEF variable

From: Eric Blake
Subject: Re: Bug #593838: AX_CFLAGS_GCC_OPTION misuses AS_VAR_PUSHDEF variable
Date: Mon, 27 Sep 2010 11:46:50 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100921 Fedora/3.1.4-1.fc13 Mnenhy/0.8.3 Thunderbird/3.1.4

On 09/25/2010 12:22 PM, Ben Pfaff wrote:
retitle 593838 AX_CFLAGS_GCC_OPTION misuses AS_VAR_PUSHDEF variable
reassign 593838 autoconf-archive

Jerome BENOIT<address@hidden>  initially reported that
AX_CFLAGS_GCC_OPTION(-std=c99) fails with Autoconf 2.67.  Vincent
Bernat<address@hidden>  determined that the bug could be fixed
by replacing a literal shell assignment by AS_VAR_SET.

Just now, I took a closer look.  I was able to reduce the problem
to the following trivial case:

--8<--------------------------cut here-------------------------->8--

    dnl This is the version used by AX_CFLAGS_GCC_OPTION.
    dnl I believe that it is incorrect.  It does not work on Autoconf>= 2.67.

You are correct that this will not work if VAR is an indirect variable name. It all depends on whether $1 is determined to be an indirection.


is direct; it expands to AS_VAR_PUSHDEF([VAR],[prefix_blah]), at which point VAR is the literal string prefix_blah, and you still have valid shell code (by sheer luck, and not because you followed the documentation). But


is indirect; it expands to AS_VAR_PUSHDEF([VAR],[prefix_$foo]), and you MUST use AS_VAR_SET([VAR]) in order to set the shell variable prefix_bar (as that is what the indirection results in). Direct use of VAR as a shell-variable name will result in invalid shell code.

On that basis, I infer that one is not supposed to use the
M4-NAME literally, and thus I believe that this is a bug in
AX_CFLAGS_GCC_OPTION.  So, I am reassigning this bug to
autoconf-archive (with this email).

That is the correct course of action.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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