readline: Adaption for NetBSD.

[Mats Erik Andersson]

Dear all,

I would like to propose a modification to the M4 file
for the module `readline', which provides a functional
detection also for NetBSD. The main obstacle is that
NetBSD uses the library `editline', and offer readline
functionality as a wrapper based on said library. The
present state of the Gnulib module is not able to detect
this properly.

We have been using a somewhat similar local script
in GNU Inetutils, successfully since four months,
but I still had to introduce changes in order to
cope with caching issues.

I found that AC_CACHE_CHECK must be performed prior
to AC_LIB_LINKFLAGS_BODY, since `-lreadline' is no
longer the basis. Also, the string `, requires ...'
must be removed to avoid duplicates; removed once
applied, that is. (Visible in OpenBSD.)

There ought to be more room for better caching,
but this is a functional starter. It behaves
correctly for GNU/Linux with and without `<readline/readline.h>'.

Best regards,
  Mats Erik Andersson, for GNU Inetutils


diff --git a/m4/readline.m4 b/m4/readline.m4
index 903886d..e2c12cc 100644
--- a/m4/readline.m4
+++ b/m4/readline.m4
@@ -1,4 +1,4 @@
-# readline.m4 serial 10
+# readline.m4 serial 11
 dnl Copyright (C) 2005-2006, 2009-2012 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -13,18 +13,18 @@ AC_DEFUN([gl_FUNC_READLINE],
   AC_REQUIRE([AC_LIB_PREPARE_PREFIX])
   AC_REQUIRE([AC_LIB_RPATH])
 
-  dnl Search for libreadline and define LIBREADLINE, LTLIBREADLINE and
-  dnl INCREADLINE accordingly.
-  AC_LIB_LINKFLAGS_BODY([readline])
+  AC_CACHE_CHECK([for readline], [gl_cv_lib_readline], [
+    dnl Search for libreadline and define LIBREADLINE, LTLIBREADLINE and
+    dnl INCREADLINE accordingly.
+    AC_LIB_LINKFLAGS_BODY([readline])
 
-  dnl Add $INCREADLINE to CPPFLAGS before performing the following checks,
-  dnl because if the user has installed libreadline and not disabled its use
-  dnl via --without-libreadline-prefix, he wants to use it. The AC_LINK_IFELSE
-  dnl will then succeed.
-  am_save_CPPFLAGS="$CPPFLAGS"
-  AC_LIB_APPENDTOVAR([CPPFLAGS], [$INCREADLINE])
+    dnl Add $INCREADLINE to CPPFLAGS before performing the following checks,
+    dnl because if the user has installed libreadline and not disabled its use
+    dnl via --without-libreadline-prefix, he wants to use it. The 
AC_LINK_IFELSE
+    dnl will then succeed.
+    am_save_CPPFLAGS="$CPPFLAGS"
+    AC_LIB_APPENDTOVAR([CPPFLAGS], [$INCREADLINE])
 
-  AC_CACHE_CHECK([for readline], [gl_cv_lib_readline], [
     gl_cv_lib_readline=no
     am_save_LIBS="$LIBS"
     dnl On some systems, -lreadline doesn't link without an additional
@@ -53,12 +53,31 @@ AC_DEFUN([gl_FUNC_READLINE],
     LIBS="$am_save_LIBS"
   ])
 
+  dnl In case of failure, examine whether libedit can act
+  dnl as replacement. Small NetBSD systems use editline
+  dnl as wrapper for readline.
+  if test "$gl_cv_lib_readline" = no; then
+    am_save_LIBS="$LIBS"
+    LIBS="$am_save_LIBS -ledit -ltermcap"
+    AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <stdio.h>
+#include <readline/readline.h>]],
+          [[readline((char*)0);]])],
+      [gl_cv_lib_readline="yes"])
+    LIBS="$am_save_LIBS"
+    dnl This wrapper does not reference libreadline at all.
+    dnl Set the correct linking according to editline(3).
+    LIBREADLINE='-ledit -ltermcap'
+    LTLIBREADLINE='-ledit -ltermcap'
+  fi
+
   if test "$gl_cv_lib_readline" != no; then
     AC_DEFINE([HAVE_READLINE], [1], [Define if you have the readline library.])
     extra_lib=`echo "$gl_cv_lib_readline" | sed -n -e 's/yes, requires //p'`
     if test -n "$extra_lib"; then
       LIBREADLINE="$LIBREADLINE $extra_lib"
       LTLIBREADLINE="$LTLIBREADLINE $extra_lib"
+      # Prevent duplicates next time around.
+      gl_cv_lib_readline=`echo "$gl_cv_lib_readline" | sed -e 
's/\(yes\).*/\1/'`
     fi
     AC_MSG_CHECKING([how to link with libreadline])
     AC_MSG_RESULT([$LIBREADLINE])