Add configure probe for rl_variable_bind().

Some exceedingly ancient readline libraries lack this function, causing
commit 3d858af07 to fail.  Per buildfarm (via Michael Paquier).

Discussion: https://postgr.es/m/E1msTLm-0007Cm-Ri@gemulon.postgresql.org

configure

@@ -17164,19 +17164,7 @@ $as_echo "#define HAVE_RL_FILENAME_QUOTING_FUNCTION 1" >>confdefs.h
 
 fi
 
-  for ac_func in rl_completion_matches rl_filename_completion_function rl_reset_screen_size
-do :
-  as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
-ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
-if eval test \"x\$"$as_ac_var"\" = x"yes"; then :
-  cat >>confdefs.h <<_ACEOF
-#define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
-_ACEOF
-
-fi
-done
-
-  for ac_func in append_history history_truncate_file
+  for ac_func in append_history history_truncate_file rl_completion_matches rl_filename_completion_function rl_reset_screen_size rl_variable_bind
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

configure.ac

@@ -2001,8 +2001,14 @@ LIBS="$LIBS_including_readline"
 
 if test "$with_readline" = yes; then
   PGAC_READLINE_VARIABLES
-  AC_CHECK_FUNCS([rl_completion_matches rl_filename_completion_function rl_reset_screen_size])
-  AC_CHECK_FUNCS([append_history history_truncate_file])
+  AC_CHECK_FUNCS(m4_normalize([
+	append_history
+	history_truncate_file
+	rl_completion_matches
+	rl_filename_completion_function
+	rl_reset_screen_size
+	rl_variable_bind
+  ]))
 fi
 
 

src/bin/psql/input.c

@@ -356,8 +356,10 @@ initializeInput(int flags)
 		/* set appropriate values for Readline's global variables */
 		initialize_readline();
 
+#ifdef HAVE_RL_VARIABLE_BIND
 		/* set comment-begin to a useful value for SQL */
 		(void) rl_variable_bind("comment-begin", "-- ");
+#endif
 
 		/* this reads ~/.inputrc, so do it after rl_variable_bind */
 		rl_initialize();

src/include/pg_config.h.in

@@ -485,6 +485,9 @@
 /* Define to 1 if you have the `rl_reset_screen_size' function. */
 #undef HAVE_RL_RESET_SCREEN_SIZE
 
+/* Define to 1 if you have the `rl_variable_bind' function. */
+#undef HAVE_RL_VARIABLE_BIND
+
 /* Define to 1 if you have the <security/pam_appl.h> header file. */
 #undef HAVE_SECURITY_PAM_APPL_H
 

src/tools/msvc/Solution.pm

@@ -354,6 +354,7 @@ sub GenerateFiles
 		HAVE_RL_FILENAME_QUOTE_CHARACTERS        => undef,
 		HAVE_RL_FILENAME_QUOTING_FUNCTION        => undef,
 		HAVE_RL_RESET_SCREEN_SIZE                => undef,
+		HAVE_RL_VARIABLE_BIND                    => undef,
 		HAVE_SECURITY_PAM_APPL_H                 => undef,
 		HAVE_SETENV                              => undef,
 		HAVE_SETPROCTITLE                        => undef,