Use GP_SLEEP_IF_TTY

Only sleep after configure warning message if the output goes to
an interactive terminal (isatty()).

This has the potential to significantly accelerate the time
configure needs to run for non-default camlib sets in the cases
where nobody is watching anyway.

Author: ndim

libgphoto2_port/gphoto-m4/gp-camlibs.m4

@@ -1,5 +1,5 @@
 # gp-camlibs.m4 - define camlibs and camlib infrastructure     -*- Autoconf -*-
-# serial 13
+# serial 14
 dnl | Increment the above serial number every time you edit this file.
 dnl | When it finds multiple m4 files with the same name,
 dnl | aclocal will use the one with the highest serial.
@@ -163,7 +163,7 @@ AC_MSG_WARN([
   #   * or even better, just build the standard set of camlibs.         #
   #=====================================================================#
 ])
-GP_SLEEP([5])
+GP_SLEEP_IF_TTY([5])
 ])
 dnl
 dnl
@@ -248,7 +248,7 @@ AS_VAR_IF([gp_sh_with_camlibs], [canon], [dnl
     # driver to prevent unnecessary support requests.              #
     #==============================================================#
 ])
-	GP_SLEEP([5])
+	GP_SLEEP_IF_TTY([5])
 ])dnl
 
 dnl set -x
@@ -308,7 +308,7 @@ do
     # 'standard' instead.                                         #
     #=============================================================#
 ])
-	GP_SLEEP([5])
+	GP_SLEEP_IF_TTY([5])
 	gp_camlib="standard"
 	;;
     esac
@@ -438,7 +438,7 @@ AS_IF([test "x$gp_camlib_set_skipping" = "x"], [dnl
     # you insist on building these camlibs.                   #
     #=========================================================#
 ])
-    GP_SLEEP([5])
+    GP_SLEEP_IF_TTY([5])
 ])
 
 GP_SET_SPACE_VAR([camlib-set], [gp_camlib_set])

libgphoto2_port/gphoto-m4/gp-progs.m4

@@ -1,5 +1,5 @@
 # gp-progs.m4 - look for certain well-known tools              -*- Autoconf -*-
-# serial 13
+# serial 14
 dnl | Increment the above serial number every time you edit this file.
 dnl | When it finds multiple m4 files with the same name,
 dnl | aclocal will use the one with the highest serial.
@@ -71,7 +71,7 @@ dnl ####################################################################
 m4_pattern_forbid([GP_PROG_SLEEP])dnl
 AC_DEFUN_ONCE([GP_PROG_SLEEP],[dnl
 AC_ARG_VAR([SLEEP], [sleep delay command])dnl
-AC_MSG_CHECKING([whether to sleep])
+AC_MSG_CHECKING([for sleep])
 AS_VAR_IF([SLEEP], [no], [dnl
   AC_MSG_RESULT([no])
 ], [dnl

libgphoto2_port/gphoto-m4/gp-sleep.m4

@@ -1,29 +1,51 @@
 # gp-sleep.m4 - look for the sleep(1) tool                     -*- Autoconf -*-
-# serial 13
+# serial 14
 dnl | Increment the above serial number every time you edit this file.
 dnl | When it finds multiple m4 files with the same name,
 dnl | aclocal will use the one with the highest serial.
 dnl
 dnl ####################################################################
 dnl GP_SLEEP(delay_in_whole_seconds)
-dnl   If the SLEEP variable is set to "no" or empty or is unset,
-dnl   do not sleep.
-dnl   If the SLEEP variable is set to something else, run that something
-dnl   else with the given delay value.
+dnl   * If the SLEEP variable is set to "no" or empty or is unset,
+dnl     do not sleep.
+dnl   * If stdout (FD 1) is not a TTY (!isatty(1)), do not sleep.
+dnl   * Otherwise, run ${SLEEP} with the given delay value argument.
 dnl ####################################################################
+dnl
+dnl ####################################################################
+dnl GP_SLEEP_IF_TTY(delay_in_whole_seconds)
+dnl   * If the SLEEP variable is set to "no" or empty or is unset,
+dnl     do not sleep.
+dnl   * If stdout (FD 1) is not a TTY (!isatty(1)), do not sleep.
+dnl   * If tty -t is not present and therefore fails, we do not lose
+dnl     much: Just that interactive users do not benefit from seeing the
+dnl     warning a bit longer.
+dnl   * Otherwise, run ${SLEEP} with the given delay value argument.
+dnl ####################################################################
+dnl
 AC_DEFUN_ONCE([_GP_SLEEP_INIT], [dnl
 AC_REQUIRE([GP_PROG_SLEEP])dnl
-AS_IF([test "x$SLEEP" != "x" && test "x$SLEEP" != "xno"], [dnl
-gp_sleep=[$]SLEEP
+AC_MSG_CHECKING([whether configure script should sleep])
+AS_IF([test "x$SLEEP" != x && test "x$SLEEP" != xno], [dnl
+  AC_MSG_RESULT([yes])
+  gp_sleep=[$]SLEEP
 ], [dnl
-gp_sleep=:
+  AC_MSG_RESULT([no])
+  gp_sleep=:
 ])
 ])dnl
 dnl
 dnl
 AC_DEFUN([GP_SLEEP], [dnl
 AC_REQUIRE([_GP_SLEEP_INIT])dnl
-$gp_sleep $1
+[$]gp_sleep $1
+])dnl
+dnl
+AC_DEFUN([GP_SLEEP_IF_TTY], [dnl
+AC_REQUIRE([_GP_SLEEP_INIT])dnl
+AS_IF([test -t 1], [dnl
+[$]gp_sleep $1
+])
 ])dnl
 dnl
 dnl