nixpkgs/pkgs/development/libraries/libical/respect-env-tzdir.patch

--- a/src/libical/icaltz-util.c	2015-06-11 15:40:58.843138630 +0200
+++ b/src/libical/icaltz-util.c	2015-06-11 15:43:12.722046252 +0200
@@ -107,7 +107,7 @@
 	char	charcnt[4];			
 } tzinfo; 
 
-static char *search_paths [] = {"/usr/share/zoneinfo","/usr/lib/zoneinfo","/etc/zoneinfo","/usr/share/lib/zoneinfo"};
+static char *search_paths [] = {"/etc/zoneinfo","/usr/share/zoneinfo","/usr/lib/zoneinfo","/usr/share/lib/zoneinfo"};
 static char *zdir = NULL;
 
 #define NUM_SEARCH_PATHS (sizeof (search_paths)/ sizeof (search_paths [0]))
@@ -194,6 +194,15 @@
 	const char *fname = ZONES_TAB_SYSTEM_FILENAME;
 	unsigned int i;
 
+	const char *env_tzdir = getenv ("TZDIR");
+	if (env_tzdir) {
+		sprintf (file_path, "%s/%s", env_tzdir, fname);
+		if (!access (file_path, F_OK|R_OK)) {
+			zdir = env_tzdir;
+			return;
+		}
+	}
+
 	for (i = 0; i < NUM_SEARCH_PATHS; i++) {
 		sprintf (file_path, "%s/%s", search_paths [i], fname);
 		if (!access (file_path, F_OK|R_OK)) {