Words in configure.ac that look like macros forbidden or merely discouraged?

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Words in configure.ac that look like macros forbidden or merely discouraged?

Gavin Smith
Hello,

In the Autoconf manual we read:

====

When you use the same text in a macro argument, you must therefore
have an extra quotation level (since one is stripped away by the macro
substitution). In general, then, it is a good idea to use double
quoting for all literal string arguments, either around just the
problematic portions, or over the entire argument:

     AC_MSG_WARN([[AC_DC] stinks  --Iron Maiden])
     AC_MSG_WARN([[AC_DC stinks  --Iron Maiden]])

However, the above example triggers a warning about a possibly
unexpanded macro when running autoconf, because it collides with the
namespace of macros reserved for the Autoconf language. To be really
safe, you can use additional escaping (either a quadrigraph, or
creative shell constructs) to silence that particular warning:

     echo "Hard rock was here!  --AC""_DC"
     AC_MSG_WARN([[AC@&t@_DC stinks  --Iron Maiden]])

====
https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Autoconf-Language.html#Autoconf-Language

Note what it says: "triggers a warning". However, it seems in some
cases, using a word that looks like it could be a macro triggers a
hard error, not just a warning:

$ autoreconf -iv
autoreconf: Entering directory `.'
autoreconf: configure.ac: not using Gettext
autoreconf: running: aclocal
configure.ac:4: warning: macro 'AM_DC' not found in library
autoreconf: configure.ac: tracing
autoreconf: configure.ac: not using Libtool
autoreconf: running: /usr/bin/autoconf
configure.ac:4: error: possibly undefined macro: AM_DC
      If this token and others are legitimate, please use m4_pattern_allow.
      See the Autoconf documentation.
autoreconf: /usr/bin/autoconf failed with exit status: 1

Any ideas which it is: is it actually forbidden, or should it be just a warning?

I intend to put information about this here:
http://buildsystem-manual.sourceforge.net/Macro-name-quoting.html#Macro-name-quoting
, which I've adapted from the test in the automake manual.

Contents of files:

$ cat configure.ac
AC_INIT([helloprog], [1.0])
AM_INIT_AUTOMAKE

echo AM_DC rocks

AC_CONFIG_FILES([Makefile])
AC_OUTPUT
$ cat Makefile.am
AUTOMAKE_OPTIONS=foreign dist-xz
$

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Re: Words in configure.ac that look like macros forbidden or merely discouraged?

Eric Blake-3
On 06/12/2016 05:25 AM, Gavin Smith wrote:
> Hello,

Apologies for just now noticing this thread.

>
> In the Autoconf manual we read:

Any reason you mailed this to the automake list, and not autoconf, then?

>
> ====
>
> When you use the same text in a macro argument, you must therefore
> have an extra quotation level (since one is stripped away by the macro
> substitution). In general, then, it is a good idea to use double
> quoting for all literal string arguments, either around just the
> problematic portions, or over the entire argument:
>
>      AC_MSG_WARN([[AC_DC] stinks  --Iron Maiden])
>      AC_MSG_WARN([[AC_DC stinks  --Iron Maiden]])
>

>
> Note what it says: "triggers a warning". However, it seems in some
> cases, using a word that looks like it could be a macro triggers a
> hard error, not just a warning:
>
> $ autoreconf -iv
> autoreconf: Entering directory `.'
> autoreconf: configure.ac: not using Gettext
> autoreconf: running: aclocal
> configure.ac:4: warning: macro 'AM_DC' not found in library
AM_DC is not the name used in the example, but falls into the namespace
reserved by automake, so I guess I see why you are testing it instead of
AC_DC.

> autoreconf: configure.ac: tracing
> autoreconf: configure.ac: not using Libtool
> autoreconf: running: /usr/bin/autoconf
> configure.ac:4: error: possibly undefined macro: AM_DC
>       If this token and others are legitimate, please use m4_pattern_allow.
>       See the Autoconf documentation.
> autoreconf: /usr/bin/autoconf failed with exit status: 1

However, the error message says that it is autoconf (not automake) that
is failing, so I don't see how this is applicable to automake.

>
> Any ideas which it is: is it actually forbidden, or should it be just a warning?

So I guess you are pointing out a documentation error in the autoconf
manual, and that the manual should call it an error, not a warning?
Sure, I can do that.

>
> I intend to put information about this here:
> http://buildsystem-manual.sourceforge.net/Macro-name-quoting.html#Macro-name-quoting
> , which I've adapted from the test in the automake manual.
>
> Contents of files:
>
> $ cat configure.ac
> AC_INIT([helloprog], [1.0])
> AM_INIT_AUTOMAKE
>
> echo AM_DC rocks
>
> AC_CONFIG_FILES([Makefile])
> AC_OUTPUT
> $ cat Makefile.am
> AUTOMAKE_OPTIONS=foreign dist-xz
> $
>
>
--
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: Words in configure.ac that look like macros forbidden or merely discouraged?

Gavin Smith
On 22 December 2016 at 19:00, Eric Blake <[hidden email]> wrote:
> On 06/12/2016 05:25 AM, Gavin Smith wrote:
>> Hello,
>
> Apologies for just now noticing this thread.
>
>>
>> In the Autoconf manual we read:
>
> Any reason you mailed this to the automake list, and not autoconf, then?

Indeed, it doesn't need automake to fail. I used automake when I
tested this before. The following configure.ac makes autoconf give an
error message:

AC_INIT([test],[0])
AC_MSG_WARN([[AC_DC] stinks  --Iron Maiden])
AC_MSG_WARN([[AC_DC stinks  --Iron Maiden]])
AC_OUTPUT

The error is

configure.ac:2: error: possibly undefined macro: AC_DC
      If this token and others are legitimate, please use m4_pattern_allow.
      See the Autoconf documentation.

>> Any ideas which it is: is it actually forbidden, or should it be just a warning?
>
> So I guess you are pointing out a documentation error in the autoconf
> manual, and that the manual should call it an error, not a warning?
> Sure, I can do that.

Either that, or autoconf could be changed to make it a warning. I
don't see any need for that, though: I think it is okay to be an
error.