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18.6.1 Changed Quotation

The most important changes are invisible to you: the implementation of most macros have completely changed. This allowed more factorization of the code, better error messages, a higher uniformity of the user’s interface etc. Unfortunately, as a side effect, some construct which used to (miraculously) work might break starting with Autoconf 2.50. The most common culprit is bad quotation.

For instance, in the following example, the message is not properly quoted: 

AC_INIT
AC_CHECK_HEADERS(foo.h, ,
  AC_MSG_ERROR(cannot find foo.h, bailing out))
AC_OUTPUT

Autoconf 2.13 simply ignores it: 

$ autoconf-2.13; ./configure --silent
creating cache ./config.cache
configure: error: cannot find foo.h
$

while Autoconf 2.50 produces a broken configure: 

$ autoconf-2.50; ./configure --silent
configure: error: cannot find foo.h
./configure: exit: bad non-numeric arg `bailing'
./configure: exit: bad non-numeric arg `bailing'
$

The message needs to be quoted, and the AC_MSG_ERROR invocation too! 

AC_INIT([Example], [1.0], [bug-example@example.org])
AC_CHECK_HEADERS([foo.h], [],
  [AC_MSG_ERROR([cannot find foo.h, bailing out])])
AC_OUTPUT

Many many (and many more) Autoconf macros were lacking proper quotation, including no less than… AC_DEFUN itself! 

$ cat configure.in
AC_DEFUN([AC_PROG_INSTALL],
[# My own much better version
])
AC_INIT
AC_PROG_INSTALL
AC_OUTPUT
$ autoconf-2.13
autoconf: Undefined macros:
***BUG in Autoconf--please report*** AC_FD_MSG
***BUG in Autoconf--please report*** AC_EPI
configure.in:1:AC_DEFUN([AC_PROG_INSTALL],
configure.in:5:AC_PROG_INSTALL
$ autoconf-2.50
$