[PATCH] lex: failure to find library for linking is a fatal error now (was: AC_PROG_LEX does not diagnose failure to find lex library)

[Stefano Lattarini]

On Sunday 15 May 2011, Stefano Lattarini wrote:
> Hello autoconfers.
> 
> It seems that AC_PROG_LEX does not diagnose a failure to find the lex
> library required to link lex-generated programs; on the contrary, when
> all the link attempts (i.e., with `-ll' and `-lfl') fail, configure
> uncorrectly declares that no lex library is needed (!), and happily
> proceeds with the configuration process -- only to then have `make' fail
> at build time.  This seems wrong to me, and is certainly definitely
> against the autoconf philosophy.
> 
> (JFTR, I've found this problem while trying to run the Automake testsuite
> on Debian using a Linux->MinGW cross compiler).
> 
> Here are the details:
> 
>  $ dpkg -l *mingw*
>  ii  gcc-mingw32       4.4.4-0.1+b2  The GNU Compiler Collection (cross 
> compiler for MingW32 / 
>  ii  mingw-w64         0~20100125-3  Minimalist GNU w64 (cross) runtime
>  ii  mingw32-binutils  2.20-0.1      Minimalist GNU win32 (cross) binutils
>  ii  mingw32-runtime   3.13-1        Minimalist GNU win32 (cross) runtime
>  $ cat > Makefile.am <<'END'
>  bin_PROGRAMS = foo
>  foo_SOURCES = foo.l
>  END
>  $ cat > configure.ac <<'END'
>  AC_INIT([foo], [1.0])
>  AM_INIT_AUTOMAKE([foreign -Wall -Werror])
>  AC_PROG_LEX
>  AC_CONFIG_FILES([Makefile])
>  AC_OUTPUT
>  END
>  $ autoreconf -vi
>  autoreconf: Entering directory `.'
>  autoreconf: configure.ac: not using Gettext
>  autoreconf: running: aclocal 
>  autoreconf: configure.ac: tracing
>  autoreconf: configure.ac: not using Libtool
>  autoreconf: running: /usr/bin/autoconf
>  autoreconf: configure.ac: not using Autoheader
>  autoreconf: running: automake --add-missing --copy --no-force
>  configure.ac:2: installing `./install-sh'
>  configure.ac:2: installing `./missing'
>  Makefile.am: installing `./depcomp'
>  configure.ac: installing `./ylwrap'
>  autoreconf: Leaving directory `.'
>  $ ./configure --host i586-mingw32msvc
>  configure: WARNING: if you wanted to set the --build type, don't use --host.
>      If a cross compiler is detected then cross compile mode will be used
>  checking for a BSD-compatible install... /usr/bin/install -c
>  checking whether build environment is sane... yes
>  checking for i586-mingw32msvc-strip... i586-mingw32msvc-strip
>  checking for a thread-safe mkdir -p... /bin/mkdir -p
>  checking for gawk... gawk
>  checking whether make sets $(MAKE)... yes
>  checking for style of include used by make... GNU
>  checking for i586-mingw32msvc-gcc... i586-mingw32msvc-gcc
>  checking whether the C compiler works... yes
>  checking for C compiler default output file name... a.exe
>  checking for suffix of executables... .exe
>  checking whether we are cross compiling... yes
>  checking for suffix of object files... o
>  checking whether we are using the GNU C compiler... yes
>  checking whether i586-mingw32msvc-gcc accepts -g... yes
>  checking for i586-mingw32msvc-gcc option to accept ISO C89... none needed
>  checking dependency style of i586-mingw32msvc-gcc... gcc3
>  checking for flex... flex
>  checking lex output file root... lex.yy
>  checking lex library... none needed # this is wrong; link failure will ensue
>  checking whether yytext is a pointer... no
>  configure: creating ./config.status
>  config.status: creating Makefile
>  config.status: executing depfiles commands
>  $ make
>  /bin/sh ./ylwrap foo.l lex.yy.c foo.c -- flex  
>  i586-mingw32msvc-gcc -DPACKAGE_NAME=\"foo\" -DPACKAGE_TARNAME=\"foo\" \
>                       -DPACKAGE_VERSION=\"1.0\" -DPACKAGE_STRING=\"foo\ 1.0\" 
> \
>                       -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" \
>                       -DPACKAGE=\"foo\" -DVERSION=\"1.0\" -I. -g -O2 \
>                       -MT foo.o -MD -MP -MF .deps/foo.Tpo -c -o foo.o foo.c
>  mv -f .deps/foo.Tpo .deps/foo.Po
>  i586-mingw32msvc-gcc  -g -O2  -o foo.exe foo.o  
>  foo.o: In function `yylex':
>  /home/stefano/tmp/lex-cross-compile-autoconf-bug/foo.c:826: undefined 
> reference to `_yywrap'
>  collect2: ld returned 1 exit status
>  make: *** [foo.exe] Error 1
> 
> Attached is the config.log resulting from the above `configure' run.
> 
> Regards,
>   Stefano
> 

The attached patch solves the problem for me.  Note that it still lacks
a testsuite addition, because I couldn't find a proper place where to
add it (it seems that the *only* place in the testsuite AC_PROG_LEX is
checked is in the file `tests/acprograms.at', using `AT_CHECK_MACRO').
If the patch is not rejected, I'll try to amend it to include a testcase.

Regards,
   Stefano

From 04b8af63fdee0eab513389a374af06a11a2e2045 Mon Sep 17 00:00:00 2001
Message-Id: <address@hidden>
From: Stefano Lattarini <address@hidden>
Date: Wed, 18 May 2011 19:38:06 +0200
Subject: [PATCH] lex: failure to find library for linking is a fatal error now

* lib/autoconf/programs.m4 (_AC_PROG_LEX_YYTEXT_DECL): Abort
configure (with exit status `77') if the library required to
link programs generated by Lex is not found.  The previous
behaviour was to simply assume that no library was needed, and
proceed with the configuration.
---
 ChangeLog                |    9 +++++++++
 lib/autoconf/programs.m4 |    8 ++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 1fca7bb..4cb6767 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2011-05-18  Stefano Lattarini  <address@hidden>
+
+       lex: failure to find library for linking is a fatal error now
+       * lib/autoconf/programs.m4 (_AC_PROG_LEX_YYTEXT_DECL): Abort
+       configure (with exit status `77') if the library required to
+       link programs generated by Lex is not found.  The previous
+       behaviour was to simply assume that no library was needed, and
+       proceed with the configuration.
+
 2011-05-05  Eric Blake  <address@hidden>
 
        doc: document dash bug with positional parameters
diff --git a/lib/autoconf/programs.m4 b/lib/autoconf/programs.m4
index fb3d8b9..1d87445 100644
--- a/lib/autoconf/programs.m4
+++ b/lib/autoconf/programs.m4
@@ -752,15 +752,19 @@ AC_SUBST([LEX_OUTPUT_ROOT], [$ac_cv_prog_lex_root])dnl
 if test -z "${LEXLIB+set}"; then
   AC_CACHE_CHECK([lex library], [ac_cv_lib_lex], [
     ac_save_LIBS=$LIBS
-    ac_cv_lib_lex='none needed'
+    ac_cv_lib_lex="none found"
     for ac_lib in '' -lfl -ll; do
       LIBS="$ac_lib $ac_save_LIBS"
       AC_LINK_IFELSE([AC_LANG_DEFINES_PROVIDED[`cat $LEX_OUTPUT_ROOT.c`]],
        [ac_cv_lib_lex=$ac_lib])
-      test "$ac_cv_lib_lex" != 'none needed' && break
+      test x"$ac_cv_lib_lex" = x && ac_cv_lib_lex="none needed"
+      test x"$ac_cv_lib_lex" != x"none found" && break
     done
     LIBS=$ac_save_LIBS
   ])
+  if test x"$ac_cv_lib_lex" = x"none found"; then
+    AC_MSG_FAILURE([cannot find library for $LEX; giving up], [77])
+  fi
   test "$ac_cv_lib_lex" != 'none needed' && LEXLIB=$ac_cv_lib_lex
 fi
 AC_SUBST(LEXLIB)
-- 
1.7.2.3