Honour an external definition of SOURCE_DATE_EPOCH when updating the embedded
modification date in TTF/TTC files.

--- a/lib/tatime.c
+++ b/lib/tatime.c
@@ -15,6 +15,8 @@
 
 #include <time.h>
 #include <stdint.h>
+#include <errno.h>
+#include <limits.h>
 
 #include "ta.h"
 
@@ -27,12 +29,51 @@ TA_get_current_time(FT_ULong* high,
 {
   /* there have been 24107 days between January 1st, 1904 (the epoch of */
   /* OpenType), and January 1st, 1970 (the epoch of the `time' function) */
-  TA_ULongLong seconds_to_1970 = 24107 * 24 * 60 * 60;
-  TA_ULongLong seconds_to_today = seconds_to_1970 + (TA_ULongLong)time(NULL);
+  const TA_ULongLong seconds_to_1970 = 24107 * 24 * 60 * 60;
+  TA_ULongLong seconds_to_build;
 
+  time_t now;
+  char *source_date_epoch, *endptr;
+  TA_ULongLong epoch;
+  source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+  if (source_date_epoch) {
+    errno = 0;
+    epoch = strtoull(source_date_epoch, &endptr, 10);
+    if ((errno == ERANGE && (epoch == ULLONG_MAX || epoch == 0))
+	|| (errno != 0 && epoch == 0)) {
+      fprintf(stderr,
+	      "Environment variable $SOURCE_DATE_EPOCH: strtoull: %s\n",
+	      strerror(errno));
+      exit(EXIT_FAILURE);
+    }
+    if (endptr == source_date_epoch) {
+      fprintf(stderr,
+	      "Environment variable $SOURCE_DATE_EPOCH: No digits were found: %s\n",
+	      endptr);
+      exit(EXIT_FAILURE);
+    }
+    if (*endptr != '\0') {
+      fprintf(stderr,
+	      "Environment variable $SOURCE_DATE_EPOCH: Trailing garbage: %s\n",
+	      endptr);
+      exit(EXIT_FAILURE);
+    }
+    if (epoch > ULONG_MAX) {
+      fprintf(stderr,
+	      "Environment variable $SOURCE_DATE_EPOCH: value must be smaller "
+	      "than or equal to: %lu but was found to be: %llu \n",
+	      ULONG_MAX, epoch);
+      exit(EXIT_FAILURE);
+    }
+    now = epoch;
+  } else {
+    now = time(NULL);
+  }
 
-  *high = (FT_ULong)(seconds_to_today >> 32);
-  *low = (FT_ULong)seconds_to_today;
+  seconds_to_build = seconds_to_1970 + (TA_ULongLong)now;
+
+  *high = (FT_ULong)(seconds_to_build >> 32);
+  *low = (FT_ULong)seconds_to_build;
 }
 
 /* end of tatime.c */
27f4ed14b44'>root</a>/<a href='/guix/log/gnu?id=1bec03df9b60f156c657a64a323ef27f4ed14b44'>gnu</a>/<a href='/guix/log/gnu/installer?id=1bec03df9b60f156c657a64a323ef27f4ed14b44'>installer</a>/<a href='/guix/log/gnu/installer/newt?id=1bec03df9b60f156c657a64a323ef27f4ed14b44'>newt</a>/<a href='/guix/log/gnu/installer/newt/hostname.scm?id=1bec03df9b60f156c657a64a323ef27f4ed14b44'>hostname.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/installer/newt/hostname.scm?id=1bec03df9b60f156c657a64a323ef27f4ed14b44&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-01-17 14:04:25 +0100'>2019-01-17</span></td><td><a href='/guix/commit/gnu/installer/newt/hostname.scm?id=d700d131be31bd2838206bfc13ddd418affb185b'>installer: Make sure every sentence is dot terminated.</a><span class='msg-avail'>...<span class='msg-tooltip'>gnu/installer/newt/hostname.scm: Finish sentences by a dot.
gnu/installer/newt/network.scm: Ditto.
gnu/installer/newt/page.scm: Ditto.
gnu/installer/newt/partition.scm: Ditto.
gnu/installer/newt/user.scm: Ditto.
gnu/installer/newt/wifi.scm: Ditto.
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2019-01-17 14:04:22 +0100'>2019-01-17</span></td><td><a href='/guix/commit/gnu/installer/newt/hostname.scm?id=5cdb6bd2db0b465fa616a9fd36760b14844d5c48'>installer: Remove "selection" from all titles.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/installer/newt/hostname.scm (run-hostname-page): Remove selection from
page title,
(run-variant-page): ditto.
* gnu/installer/newt/keymap.scm (run-layout-page): Ditto.
* gnu/installer/newt/locale.scm (run-layout-page): Ditto,
(run-territory-page): ditto,
(run-codeset-page): ditto,
(run-modifier-page): ditto
* gnu/installer/newt/network.scm (run-territory-page): Ditto.
* gnu/installer/newt/timezone.scm (run-timezone-page): Ditto.
* gnu/installer/newt/wifi.scm (run-wifi-page): Ditto.
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2019-01-17 14:04:20 +0100'>2019-01-17</span></td><td><a href='/guix/commit/gnu/installer/newt/hostname.scm?id=d0f3a672dcbdfefd3556b6a21985ff0e35eed3be'>gnu: Add graphical installer support.</a><span class='msg-avail'>...<span class='msg-tooltip'>* configure.ac: Require that guile-newt is available.
* gnu/installer.scm: New file.
* gnu/installer/aux-files/logo.txt: New file.
* gnu/installer/build-installer.scm: New file.
* gnu/installer/connman.scm: New file.
* gnu/installer/keymap.scm: New file.
* gnu/installer/locale.scm: New file.
* gnu/installer/newt.scm: New file.
* gnu/installer/newt/ethernet.scm: New file.
* gnu/installer/newt/hostname.scm: New file.
* gnu/installer/newt/keymap.scm: New file.
* gnu/installer/newt/locale.scm: New file.
* gnu/installer/newt/menu.scm: New file.
* gnu/installer/newt/network.scm: New file.
* gnu/installer/newt/page.scm: New file.
* gnu/installer/newt/timezone.scm: New file.
* gnu/installer/newt/user.scm: New file.
* gnu/installer/newt/utils.scm: New file.
* gnu/installer/newt/welcome.scm: New file.
* gnu/installer/newt/wifi.scm: New file.
* gnu/installer/steps.scm: New file.
* gnu/installer/timezone.scm: New file.
* gnu/installer/utils.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add previous files.
* gnu/system.scm: Export %root-account.
* gnu/system/install.scm (%installation-services): Use kmscon instead of linux
VT for all tty.
(installation-os)[users]: Add the graphical installer as shell of the root
account.
[packages]: Add font related packages.
* po/guix/POTFILES.in: Add installer files.
</span></span></td><td>Mathieu Othacehe</td></tr>