Re: Bug#395466: AM_PATH_CHECK causes "possibly undefined macro" errors

[Josh Triplett]

Ralf Wildenhues wrote:
> [ http://bugs.debian.org/395466 ]
> 
> Hello Josh,
> 
> * Josh Triplett wrote on Fri, Oct 27, 2006 at 09:33:30AM CEST:
>> --- check.m4.orig    2006-10-13 12:24:41.000000000 -0700
>> +++ check.m4 2006-10-26 23:55:54.000000000 -0700
>> @@ -4,8 +4,9 @@
>>  
>>  AC_DEFUN([AM_PATH_CHECK],
>>  [
>> -  AC_MSG_WARN([[AM_PATH_CHECK() is deprecated]])
>> -  AC_MSG_WARN([[use PKG_CHECK_MODULES([CHECK], [check >= 0.9.4]) instead]])
>> +  empty=
>> +  AC_MSG_WARN([A${empty}M_PATH_CHECK() is deprecated])
>> +  AC_MSG_WARN([[use P${empty}KG_CHECK_MODULES([CHECK], [check >= 0.9.4]) 
>> instead]])
>>    AC_ARG_WITH([check],
>>    [  --with-check=PATH       prefix where check is installed 
>> [default=auto]])
>>   
> 
> Yuck three times.  1. Learn to use Quadrigraphs:
>   AC_MSG_WARN([[AM@&address@hidden() is deprecated]])
> 
> http://www.gnu.org/software/autoconf/manual/html_node/Quadrigraphs.html

Ah, much better, thanks.  This change seems to work, and has the additional
advantage of not affecting the generated configure script.  Revised patch
attached.

> 2. Double quotation [[ ]] does successfully prevent expansion of macros,
> iff all macros calling this one have been quoted correctly, i.e., once.

In this case, only the top-level configure.ac calls AM_PATH_CHECK, and it
just includes a line "AM_PATH_CHECK", with no quoting.  The double
quotation did successfully prevent macro expansion; it just didn't prevent
autoconf from noticing those unexpanded macro names and complaining about
them.

> 3. m4_pattern_forbid was invented to forbid some patterns.  User macros
> should simply not begin with 'AM_'.  That prefix is reserved for
> Automake, and also used by a set of legacy macros from some other
> packages.  When you invent new names, use a different prefix, like
> 'jt_', or, for pkg-config, 'PKG_'.  I reckon that the damage is already
> done with AM_PATH_CHECK though.  Which is the name of the package that
> defines it?  It is broken, the bug should be moved to this package, and
> to fix it, the package should add something like
>   m4_pattern_allow([^AM_PATH_CHECK$])
> to its macro.

The check package defined AM_PATH_CHECK, and has now deprecated it in
favor of a pkg-config file and the use of PKG_CHECK_MODULES as the
warning message indicates.  However, existing software using check relies
on the current AM_PATH_CHECK macro.

m4_pattern_allow seems like the wrong approach here, for two reasons:
* In order to solve this bug, check.m4 would need to use
  m4_pattern_allow for PKG_CHECK_MODULES as well, which seems very wrong.
* m4_pattern_allow would disable the normal behavior of complaining about
  unexpanded symbols in these two cases, which could leave errors undetected
  at autoconf time, and generate a broken configure script with these macros
  unexpanded in other places.

I think your suggested quadrigraph solution works best in this case.

- Josh Triplett

--- check.m4.orig       2006-10-13 12:24:41.000000000 -0700
+++ check.m4    2006-10-27 13:38:23.000000000 -0700
@@ -4,8 +4,8 @@
 
 AC_DEFUN([AM_PATH_CHECK],
 [
-  AC_MSG_WARN([[AM_PATH_CHECK() is deprecated]])
-  AC_MSG_WARN([[use PKG_CHECK_MODULES([CHECK], [check >= 0.9.4]) instead]])
+  AC_MSG_WARN([A@&address@hidden() is deprecated])
+  AC_MSG_WARN([[use P@&address@hidden([CHECK], [check >= 0.9.4]) instead]])
   AC_ARG_WITH([check],
   [  --with-check=PATH       prefix where check is installed [default=auto]])

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