commit 078aab706d8a41c587519e7a2b362ac00b774c26
Author: Damien Regad <dregad@mantisbt.org>
Date:   2014-10-14 16:38:34 +0200

    ALT FIX: timezone initialization in core.php
    
    This is my original proposed fix, vs the one that was implemented in
    master which is based on grangeway's proposal.
    
    Prior to this, core.php would trigger a PHP warning on PHP >= 5.3 when
    date_default_timezone_get() is not able to determine the timezone and
    defaults to UTC (e.g. when php.ini date.timezone is not set).
    
    The timezone is determined in the following order
      1. user preferences
      2. MantisBT configuration ($g_default_timezone)
      3. php.ini setting (date.timezone)
      4. UTC (set by date_default_timezone_get())
    
    Fixes #17747

diff --git a/core.php b/core.php
index 8c31462..fc53e95 100644
--- a/core.php
+++ b/core.php
@@ -238,22 +238,31 @@ if( !isset( $g_login_anonymous ) ) {
 
 # Set the current timezone
 if( !defined( 'MANTIS_MAINTENANCE_MODE' ) ) {
-	require_api( 'authentication_api.php' );
-
-	# To reduce overhead, we assume that the timezone configuration is valid,
-	# i.e. it exists in timezone_identifiers_list(). If not, a PHP NOTICE will
-	# be raised. Use admin checks to validate configuration.
-	@date_default_timezone_set( config_get_global( 'default_timezone' ) );
-	$t_tz = @date_default_timezone_get();
-	config_set_global( 'default_timezone', $t_tz, true );
+	# Get MantisBT default timezone
+	$t_default_timezone = config_get_global( 'default_timezone' );
+	if( !in_array( $t_default_timezone, timezone_identifiers_list() ) ) {
+		# If not valid, fallback to system timezone, or UTC if not set
+		$t_default_timezone = @date_default_timezone_get();
+		config_set_global( 'default_timezone', $t_default_timezone, true );
+	}
 
+	# Now determine current timezone according to user's preferences
+	require_api( 'authentication_api.php' );
 	if( auth_is_user_authenticated() ) {
 		# Determine the current timezone according to user's preferences
 		require_api( 'user_pref_api.php' );
-		$t_tz = user_pref_get_pref( auth_get_current_user_id(), 'timezone' );
-		@date_default_timezone_set( $t_tz );
+		$t_user_timezone = user_pref_get_pref( auth_get_current_user_id(), 'timezone' );
+
+		# fallback to default timezone if not valid
+		if( in_array( $t_user_timezone, timezone_identifiers_list() ) ) {
+			$t_user_timezone = $t_default_timezone;
+		}
+	} else {
+		$t_user_timezone = $t_default_timezone;
 	}
-	unset( $t_tz );
+
+	date_default_timezone_set( $t_user_timezone );
+	unset( $t_user_timezone, $t_default_timezone );
 }
 
 # Cache current user's collapse API data