New configure test for flex, which recognizes only flex but does so in all

incarnations (I hope). When an acceptable flex version is not found, print
instructive error messages from both configure and the makefiles, so that
users can continue building anyway.

aclocal.m4

@@ -1,4 +1,4 @@
-# $Header: /cvsroot/pgsql/aclocal.m4,v 1.5 2000/08/27 19:00:00 petere Exp $
+# $Header: /cvsroot/pgsql/aclocal.m4,v 1.6 2000/08/28 11:53:12 petere Exp $
 # This comes from the official Autoconf macro archive at
 # <http://research.cys.de/autoconf-archive/>
 # (I removed the $ before the Id CVS keyword below.)
@@ -65,7 +65,7 @@ extern accept ($ac_cv_func_accept_arg1, $ac_cv_func_accept_arg2, $ac_cv_func_acc
  AC_DEFINE_UNQUOTED(ACCEPT_TYPE_ARG3,$ac_cv_func_accept_arg3)
 ])
 # Macros to detect C compiler features
-# $Header: /cvsroot/pgsql/aclocal.m4,v 1.5 2000/08/27 19:00:00 petere Exp $
+# $Header: /cvsroot/pgsql/aclocal.m4,v 1.6 2000/08/28 11:53:12 petere Exp $
 
 
 
@@ -154,7 +154,7 @@ undefine([AC_TYPE_NAME])dnl
 undefine([AC_CV_NAME])dnl
 ])# PGAC_CHECK_ALIGNOF
 # Macros that test various C library quirks
-# $Header: /cvsroot/pgsql/aclocal.m4,v 1.5 2000/08/27 19:00:00 petere Exp $
+# $Header: /cvsroot/pgsql/aclocal.m4,v 1.6 2000/08/28 11:53:12 petere Exp $
 
 
 # PGAC_VAR_INT_TIMEZONE
@@ -233,7 +233,7 @@ fi
 HAVE_POSIX_SIGNALS=$pgac_cv_func_posix_signals
 AC_SUBST(HAVE_POSIX_SIGNALS)])# PGAC_FUNC_POSIX_SIGNALS
 # Macros to detect certain C++ features
-# $Header: /cvsroot/pgsql/aclocal.m4,v 1.5 2000/08/27 19:00:00 petere Exp $
+# $Header: /cvsroot/pgsql/aclocal.m4,v 1.6 2000/08/28 11:53:12 petere Exp $
 
 
 # PGAC_CLASS_STRING
@@ -299,10 +299,82 @@ AC_LANG_RESTORE])
 if test $pgac_cv_cxx_namespace_std = yes ; then
     AC_DEFINE(HAVE_NAMESPACE_STD, 1, [Define to 1 if the C++ compiler understands `using namespace std'])
 fi])# PGAC_CXX_NAMESPACE_STD
+# $Header: /cvsroot/pgsql/aclocal.m4,v 1.6 2000/08/28 11:53:12 petere Exp $
+
+
+# PGAC_PATH_FLEX
+# --------------
+# Look for Flex, set the output variable FLEX to its path if found.
+# Avoid the buggy version 2.5.3. Also find Flex if its installed
+# under `lex', but do not accept other Lex programs.
+
+AC_DEFUN([PGAC_PATH_FLEX],
+[AC_CACHE_CHECK([for flex], pgac_cv_path_flex,
+[# Let the user override the test
+if test -n "$FLEX"; then
+  pgac_cv_path_flex=$FLEX
+else
+  pgac_save_IFS=$IFS
+  IFS=:
+  for pgac_dir in $PATH; do
+    if test -z "$pgac_dir" || test x"$pgac_dir" = x"."; then
+      pgac_dir=`pwd`
+    fi
+    for pgac_prog in flex lex; do
+      pgac_candidate="$pgac_dir/$pgac_prog"
+      if test -f "$pgac_candidate" \
+        && $pgac_candidate --version >/dev/null 2>&1
+      then
+        echo '%%'  > conftest.l
+        if $pgac_candidate -t conftest.l 2>/dev/null | grep FLEX_SCANNER >/dev/null 2>&1; then
+          if $pgac_candidate --version | grep '2\.5\.3' >/dev/null 2>&1; then
+            pgac_broken_flex=$pgac_candidate
+            continue
+          fi
+
+          pgac_cv_path_flex=$pgac_candidate
+          break 2
+        fi
+      fi
+    done
+  done
+  IFS=$pgac_save_IFS
+  rm -f conftest.l
+  : ${pgac_cv_path_flex=no}
+fi
+])[]dnl AC_CACHE_CHECK
+
+if test x"$pgac_cv_path_flex" = x"no"; then
+  if test -n "$pgac_broken_flex"; then
+    AC_MSG_WARN([
+***
+The Flex version 2.5.3 you have at $pgac_broken_flex contains a bug. You
+should get version 2.5.4 or later.
+###])
+  fi
+
+  AC_MSG_WARN([
+***
+Without Flex you won't be able to build PostgreSQL from scratch, or change
+any of the scanner definition files. You can obtain Flex from a GNU mirror
+site. (If you are using the official distribution of PostgreSQL then you
+do not need to worry about this because the lexer files are pre-generated.)
+***])
+fi
+
+if test x"$pgac_cv_path_flex" = x"no"; then
+  FLEX=
+else
+  FLEX=$pgac_cv_path_flex
+fi
+
+AC_SUBST(FLEX)
+AC_SUBST(FLEXFLAGS)
+])# PGAC_PATH_FLEX
 #
 # Autoconf macros for configuring the build of Python extension modules
 #
-# $Header: /cvsroot/pgsql/aclocal.m4,v 1.5 2000/08/27 19:00:00 petere Exp $
+# $Header: /cvsroot/pgsql/aclocal.m4,v 1.6 2000/08/28 11:53:12 petere Exp $
 #
 
 # PGAC_PROG_PYTHON