build: Detect appropriate strftime() year modifier at build time

Different libc implementations (or different platforms) have different
bugs. Even though %Y is documented as a 4-digit number, and %C as
year/100 in a [00-99] range, they both crap out with years under 1000,
using respectively 3 and 1 digits.

This would be typically task for a width modifier (e.g. %4Y, or %2C),
but that was conversely found to break NixOS on Darwin.

Since the existing libc bugs paint us to a corner, detect an
appropriate modifier at build time to get a 4-digit year to get true
ISO 8601 in our supported [0001-9999] year range.

Closes: https://gitlab.gnome.org/GNOME/tracker/-/issues/402

3 files changed, 40 insertions, 2 deletions

diff --git a/config.h.meson.in b/config.h.meson.in
index df4b880b0..2faa1a586 100644
--- a/config.h.meson.in
+++ b/config.h.meson.in
@@ -51,3 +51,6 @@
 
 /* Whether RTLD_NOLOAD is defined */
 #mesondefine HAVE_RTLD_NOLOAD
+
+/* Appropriate 4-digit year modifier for strftime() */
+#mesondefine STRFTIME_YEAR_MODIFIER
diff --git a/meson.build b/meson.build
index 3c147c8f3..6a7f8e133 100644
--- a/meson.build
+++ b/meson.build
@@ -199,6 +199,39 @@ else
 endif
 
 ##################################################################
+# Get an appropriate 4-digit year modifier for strftime
+##################################################################
+result = cc.run('''
+  #include <stdio.h>
+  #include <string.h>
+  #include <time.h>
+
+  int main (int argc, char *argv[]) {
+    char *modifiers[] = { "%Y", "%C%y", "%4Y", "%2C%y", NULL };
+    time_t timestamp = -58979923200; /* 0101-01-01T01:01:01Z */
+    char *buf[100];
+    struct tm tm;
+    int i;
+    gmtime_r (&timestamp, &tm);
+    for (i = 0; modifiers[i]; i++) {
+      strftime (&buf, sizeof buf, modifiers[i], &tm);
+      if (strcmp (&buf, "0101") == 0) {
+        printf ("%s", modifiers[i]);
+	return 0;
+      }
+    }
+    return -1;
+  }
+  ''',
+  name: 'strftime 4-digit year modifier')
+
+if not result.compiled() or result.returncode() != 0
+  error('Libc implementation has broken 4-digit years implementation.')
+else
+  year_modifier = result.stdout()
+endif
+
+##################################################################
 # Check for libtracker-data and libtracker-fts: Unicode support
 #
 # By default, AUTO with this order of preference:
@@ -306,6 +339,7 @@ conf.set('TRACKER_MINOR_VERSION', tracker_minor_version)
 conf.set('TRACKER_MICRO_VERSION', tracker_micro_version)
 conf.set('TRACKER_INTERFACE_AGE', 0)
 conf.set('TRACKER_BINARY_AGE', 100 * tracker_minor_version + tracker_micro_version)
+conf.set('STRFTIME_YEAR_MODIFIER', '"@0@"'.format(year_modifier))
 
 # Check for RTLD_NOLOAD
 have_rtld_noload = cc.has_header_symbol('dlfcn.h', 'RTLD_NOLOAD')
@@ -399,6 +433,7 @@ summary = [
   '    Debug:                                  ' + get_option('debug').to_string(),
   '    Optimization:                           ' + get_option('optimization'),
   '    Compiler:                               ' + cc.get_id(),
+  '    4-digit strftime() year modifier:       ' + year_modifier,
   '\nFeature Support:',
   '    Unicode support library:                ' + unicode_library_name,
   '    Build with Stemming support:            ' + have_libstemmer.to_string(),
diff --git a/src/libtracker-sparql/core/tracker-db-interface-sqlite.c b/src/libtracker-sparql/core/tracker-db-interface-sqlite.c
index 2aa493ca9..25e2c519f 100644
--- a/src/libtracker-sparql/core/tracker-db-interface-sqlite.c
+++ b/src/libtracker-sparql/core/tracker-db-interface-sqlite.c
@@ -1624,9 +1624,9 @@ function_sparql_print_value (sqlite3_context *context,
 				result_context_function_error (context, fn, "Invalid unix timestamp");
 
 			if (prop_type == TRACKER_PROPERTY_TYPE_DATETIME)
-				retval = strftime ((gchar *) &buf, sizeof (buf), "%2C%y-%m-%dT%TZ", &tm);
+				retval = strftime ((gchar *) &buf, sizeof (buf), STRFTIME_YEAR_MODIFIER "-%m-%dT%TZ", &tm);
 			else if (prop_type == TRACKER_PROPERTY_TYPE_DATE)
-				retval = strftime ((gchar *) &buf, sizeof (buf), "%2C%y-%m-%d", &tm);
+				retval = strftime ((gchar *) &buf, sizeof (buf), STRFTIME_YEAR_MODIFIER "-%m-%d", &tm);
 			else
 				g_assert_not_reached ();