Non-fatal Boost detection failures

[mdeters]

We want to provide support for conditional Boost support---in particular, we require Boost for one of our projects, but Boost threading is optionally supported. To support this, we've modified boost.m4's BOOST_FIND_LIB and BOOST_THREADS to run an optionally-provided ACTION-IF-NOT-FOUND (if not provided, the usual AC_MSG_ERROR behavior is retained). Patch follows in a comment. Thanks!

[mdeters]

diff --git a/build-aux/boost.m4 b/build-aux/boost.m4
index 3d4e47c..6252f96 100644
--- a/build-aux/boost.m4
+++ b/build-aux/boost.m4
@@ -265,13 +265,14 @@ fi

BOOST_FIND_LIB([LIB-NAME], [PREFERRED-RT-OPT], [HEADER-NAME], [CXX-TEST],

-# [CXX-PROLOGUE])
+# [CXX-PROLOGUE], [ACTION-IF-NOT-FOUND])

-------------------------------------------------------------------------

Look for the Boost library LIB-NAME (e.g., LIB-NAME = `thread', for

libboost_thread). Check that HEADER-NAME works and check that

libboost_LIB-NAME can link with the code CXX-TEST. The optional argument

CXX-PROLOGUE can be used to include some C++ code before the`main'

-# function.
+# function. If ACTION-IF-NOT-FOUND is given, errors are nonfatal (otherwise
+# they are fatal).

Invokes BOOST_FIND_HEADER([HEADER-NAME]) (see above).

@@ -299,7 +300,7 @@ AS_VAR_PUSHDEF([Boost_lib], [boost_cv_lib_$1])dnl
AS_VAR_PUSHDEF([Boost_lib_LDFLAGS], [boost_cv_lib_$1_LDFLAGS])dnl
AS_VAR_PUSHDEF([Boost_lib_LDPATH], [boost_cv_lib_$1_LDPATH])dnl
AS_VAR_PUSHDEF([Boost_lib_LIBS], [boost_cv_lib_$1_LIBS])dnl
-BOOST_FIND_HEADER([$3])
+BOOST_FIND_HEADER([$3], [$6])
boost_save_CPPFLAGS=$CPPFLAGS
CPPFLAGS="$CPPFLAGS $BOOST_CPPFLAGS"

Now let's try to find the library. The algorithm is as follows: first look

@@ -355,7 +356,9 @@ dnl empty because the test file is generated only once above (before we
dnl start the for loops).
AC_COMPILE_IFELSE([],
[ac_objext=do_not_rm_me_plz],

• [AC_MSG_ERROR([cannot compile a test that uses Boost $1])])
• [m4_if([$6], [], [AC_MSG_ERROR([cannot compile a test that uses Boost $1])],

•                  [AC_MSG_NOTICE([cannot compile a test that uses Boost $1])])
  

• $6])
  

  ac_objext=$boost_save_ac_objext
  boost_failed_libs=

  Don't bother to ident the 6 nested for loops, only the 2 innermost ones

  @@ -419,7 +422,9 @@ rm -f conftest.$ac_objext
  ])
  case $Boost_lib in #(
  no) _AC_MSG_LOG_CONFTEST
• AC_MSG_ERROR([cannot find the flags to link with Boost $1])
• m4_if([$6], [], [AC_MSG_ERROR([cannot find the flags to link with Boost $1])],

•                [AC_MSG_NOTICE([cannot find the flags to link with Boost $1])])
  

• $6
  ;;
  esac
  AC_SUBST(AS_TR_CPP([BOOST_$1_LDFLAGS]), [$Boost_lib_LDFLAGS])dnl
  @@ -825,10 +830,11 @@ BOOST_FIND_LIB([unit_test_framework], [$1],
  ])# BOOST_TEST

-# BOOST_THREADS([PREFERRED-RT-OPT])
-# ---------------------------------
+# BOOST_THREADS([PREFERRED-RT-OPT], [ACTION-IF-NOT-FOUND])
+# --------------------------------------------------------

Look for Boost.Thread. For the documentation of PREFERRED-RT-OPT, see the

-# documentation of BOOST_FIND_LIB above.
+# documentation of BOOST_FIND_LIB above. If ACTION-IF-NOT-FOUND is given,
+# errors are non-fatal; if it's absent, errors are fatal.

FIXME: Provide an alias "BOOST_THREAD".

BOOST_DEFUN([Threads],
[dnl Having the pthread flag is required at least on GCC3 where
@@ -857,14 +863,14 @@ CPPFLAGS="$CPPFLAGS $boost_cv_pthread_flag"
case $host_os in
(mingw)
BOOST_FIND_LIB([thread_win32], [$1],

•               [boost/thread.hpp], [boost::thread t; boost::mutex m;])
  

•               [boost/thread.hpp], [boost::thread t; boost::mutex m;], [], [$2])
  

  BOOST_THREAD_LDFLAGS=$BOOST_THREAD_WIN32_LDFLAGS
  BOOST_THREAD_LDPATH=$BOOST_THREAD_WIN32_LDPATH
  BOOST_THREAD_LIBS=$BOOST_THREAD_WIN32_LIBS
  ;;
  (*)
  BOOST_FIND_LIB([thread], [$1],

•               [boost/thread.hpp], [boost::thread t; boost::mutex m;])
  

•               [boost/thread.hpp], [boost::thread t; boost::mutex m;], [], [$2])
  

  ;;
  esac