Stop calling res_init

Emacs shouldn’t need to call res_init any more, now that nscd or
equivalent is everywhere.  On modern systems, calling res_init
simply slows Emacs down.  On ancient systems lacking nscd Emacs
will still work well enough with this change; it’s just that it
won’t respond to changes in /etc/resolv.conf.
* configure.ac (HAVE_RES_INIT): Remove.  Worry about -lresolv only
when configured --with-hesiod.  Hesiod is still used; see, e.g.:
https://soylentnews.org/meta/article.pl?sid=15/07/13/0255214
* src/Makefile.in (LIBRESOLV): Remove.  All uses removed.

admin/CPP-DEFINES

@@ -254,7 +254,6 @@ HAVE_RANDOM
 HAVE_READLINK
 HAVE_READLINKAT
 HAVE_RECVFROM
-HAVE_RES_INIT
 HAVE_RINT
 HAVE_RSVG
 HAVE_SELECT

configure.ac

@@ -4000,44 +4000,13 @@ AC_CACHE_CHECK([whether signals can be handled on alternate stack],
      [emacs_cv_alternate_stack=yes],
      [emacs_cv_alternate_stack=no])])
 
-# Do we have res_init, for detecting changes in /etc/resolv.conf?
-# On Darwin, res_init appears not to be useful: see bug#562 and
-# http://lists.gnu.org/archive/html/emacs-devel/2007-11/msg01467.html
-resolv=no
-
-if test $opsys != darwin; then
-
-  AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <netinet/in.h>
-#include <arpa/nameser.h>
-#include <resolv.h>]],
-    [[return res_init();]])],
-    have_res_init=yes, have_res_init=no)
-  if test "$have_res_init" = no; then
-    OLIBS="$LIBS"
-    LIBS="$LIBS -lresolv"
-    AC_MSG_CHECKING(for res_init with -lresolv)
-    AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <netinet/in.h>
-#include <arpa/nameser.h>
-#include <resolv.h>]],
-      [[return res_init();]])],
-      have_res_init=yes, have_res_init=no)
-    AC_MSG_RESULT($have_res_init)
-    if test "$have_res_init" = yes ; then
-      resolv=yes
-    fi
-    LIBS="$OLIBS"
-  fi
-
-  if test "$have_res_init" = yes; then
-    AC_DEFINE(HAVE_RES_INIT, 1, [Define to 1 if res_init is available.])
-  fi
-fi                              dnl !darwin
-
 # Do we need the Hesiod library to provide the support routines?
 dnl FIXME?  Should we be skipping this on Darwin too?
 LIBHESIOD=
+LIBRESOLV=
 if test "$with_hesiod" != no ; then
   # Don't set $LIBS here -- see comments above.  FIXME which comments?
+  resolv=no
   AC_CHECK_FUNC(res_send, , [AC_CHECK_FUNC(__res_send, ,
      [AC_CHECK_LIB(resolv, res_send, resolv=yes,
 		  [AC_CHECK_LIB(resolv, __res_send, resolv=yes)])])])
@@ -4046,21 +4015,16 @@ if test "$with_hesiod" != no ; then
   else
     RESOLVLIB=
   fi
+  hesiod=no
   AC_CHECK_FUNC(hes_getmailhost, , [AC_CHECK_LIB(hesiod, hes_getmailhost,
 	hesiod=yes, :, $RESOLVLIB)])
 
   if test x"$hesiod" = xyes; then
     LIBHESIOD=-lhesiod
+    LIBRESOLV=$RESOLVLIB
   fi
 fi
 AC_SUBST(LIBHESIOD)
-
-# Do we need libresolv (due to res_init or Hesiod)?
-if test "$resolv" = yes && test $opsys != darwin; then
-  LIBRESOLV=-lresolv
-else
-  LIBRESOLV=
-fi
 AC_SUBST(LIBRESOLV)
 
 # These tell us which Kerberos-related libraries to use.

src/Makefile.in

@@ -302,9 +302,6 @@ CM_OBJ=@CM_OBJ@
 
 LIBGPM = @LIBGPM@
 
-## -lresolv, or empty.
-LIBRESOLV = @LIBRESOLV@
-
 LIBSELINUX_LIBS = @LIBSELINUX_LIBS@
 
 LIBGNUTLS_LIBS = @LIBGNUTLS_LIBS@
@@ -485,7 +482,7 @@ LIBES = $(LIBS) $(W32_LIBS) $(LIBS_GNUSTEP) $(LIBX_BASE) $(LIBIMAGE) \
    $(WEBKIT_LIBS) \
    $(LIB_EACCESS) $(LIB_FDATASYNC) $(LIB_TIMER_TIME) $(DBUS_LIBS) \
    $(LIB_EXECINFO) $(XRANDR_LIBS) $(XINERAMA_LIBS) $(XFIXES_LIBS) \
-   $(LIBXML2_LIBS) $(LIBGPM) $(LIBRESOLV) $(LIBS_SYSTEM) $(CAIRO_LIBS) \
+   $(LIBXML2_LIBS) $(LIBGPM) $(LIBS_SYSTEM) $(CAIRO_LIBS) \
    $(LIBS_TERMCAP) $(GETLOADAVG_LIBS) $(SETTINGS_LIBS) $(LIBSELINUX_LIBS) \
    $(FREETYPE_LIBS) $(FONTCONFIG_LIBS) $(LIBOTF_LIBS) $(M17N_FLT_LIBS) \
    $(LIBGNUTLS_LIBS) $(LIB_PTHREAD) $(GETADDRINFO_A_LIBS) \

src/process.c

@@ -75,11 +75,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 # include <sys/stropts.h>
 #endif
 
-#ifdef HAVE_RES_INIT
-#include <arpa/nameser.h>
-#include <resolv.h>
-#endif
-
 #ifdef HAVE_UTIL_H
 #include <util.h>
 #endif
@@ -3827,10 +3822,6 @@ usage: (make-network-process &rest ARGS)  */)
       immediate_quit = 1;
       QUIT;
 
-#ifdef HAVE_RES_INIT
-      res_init ();
-#endif
-
       struct addrinfo hints;
       memset (&hints, 0, sizeof hints);
       hints.ai_family = family;
@@ -3910,10 +3901,6 @@ usage: (make-network-process &rest ARGS)  */)
       immediate_quit = 1;
       QUIT;
 
-#ifdef HAVE_RES_INIT
-      res_init ();
-#endif
-
       host_info_ptr = gethostbyname ((const char *) SDATA (host));
       immediate_quit = 0;