From 569dc0de50a46b64763921199a2706ab34d151a9 Mon Sep 17 00:00:00 2001
From: Edward Welbourne <edward.welbourne@qt.io>
Date: Mon, 11 Sep 2023 11:41:39 +0200
Subject: [PATCH] Support the TZDIR environment variable

On Linux / glibc, this overrides the default system location for the
zone info. So check for files there first. Break out a function to
manage the trying of (now three) zoneinfo directories when opening a
file by name relative to there.

Pick-to: 6.6 6.5
Task-number: QTBUG-116017
Change-Id: I1f97107aabd9015c0a5543639870f1d70654ca67
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/time/qtimezoneprivate_tz.cpp | 71 ++++++++++++++++--------
 1 file changed, 48 insertions(+), 23 deletions(-)

diff --git a/src/corelib/time/qtimezoneprivate_tz.cpp b/src/corelib/time/qtimezoneprivate_tz.cpp
index e702a5d6b4..2b54cf7a5e 100644
--- a/src/corelib/time/qtimezoneprivate_tz.cpp
+++ b/src/corelib/time/qtimezoneprivate_tz.cpp
@@ -51,17 +51,41 @@ typedef QHash<QByteArray, QTzTimeZone> QTzTimeZoneHash;
 
 static bool isTzFile(const QString &name);
 
+// Open a named file under the zone info directory:
+static bool openZoneInfo(QString name, QFile *file)
+{
+    // At least on Linux / glibc (see man 3 tzset), $TZDIR overrides the system
+    // default location for zone info:
+    const QString tzdir = qEnvironmentVariable("TZDIR");
+    if (!tzdir.isEmpty()) {
+        file->setFileName(QDir(tzdir).filePath(name));
+        if (file->open(QIODevice::ReadOnly))
+            return true;
+    }
+    // Try modern system path first:
+    constexpr auto zoneShare = "/usr/share/zoneinfo/"_L1;
+    if (tzdir != zoneShare && tzdir != zoneShare.chopped(1)) {
+        file->setFileName(zoneShare + name);
+        if (file->open(QIODevice::ReadOnly))
+            return true;
+    }
+    // Fall back to legacy system path:
+    constexpr auto zoneLib = "/usr/lib/zoneinfo/"_L1;
+    if (tzdir != zoneLib && tzdir != zoneLib.chopped(1)) {
+        file->setFileName(zoneShare + name);
+        if (file->open(QIODevice::ReadOnly))
+            return true;
+    }
+    return false;
+}
+
 // Parse zone.tab table for territory information, read directories to ensure we
 // find all installed zones (many are omitted from zone.tab; even more from
 // zone1970.tab).
 static QTzTimeZoneHash loadTzTimeZones()
 {
-    QString path = QStringLiteral("/usr/share/zoneinfo/zone.tab");
-    if (!QFile::exists(path))
-        path = QStringLiteral("/usr/lib/zoneinfo/zone.tab");
-
-    QFile tzif(path);
-    if (!tzif.open(QIODevice::ReadOnly))
+    QFile tzif;
+    if (!openZoneInfo("zone.tab"_L1, &tzif))
         return QTzTimeZoneHash();
 
     QTzTimeZoneHash zonesHash;
@@ -91,6 +115,7 @@ static QTzTimeZoneHash loadTzTimeZones()
         }
     }
 
+    const QString path = tzif.fileName();
     const qsizetype cut = path.lastIndexOf(u'/');
     Q_ASSERT(cut > 0);
     const QDir zoneDir = QDir(path.first(cut));
@@ -772,20 +797,13 @@ QTzTimeZoneCacheEntry QTzTimeZoneCache::findEntry(const QByteArray &ianaId)
         tzif.setFileName(QStringLiteral("/etc/localtime"));
         if (!tzif.open(QIODevice::ReadOnly))
             return ret;
-    } else {
-        // Open named tz, try modern path first, if fails try legacy path
-        tzif.setFileName("/usr/share/zoneinfo/"_L1 + QString::fromLocal8Bit(ianaId));
-        if (!tzif.open(QIODevice::ReadOnly)) {
-            tzif.setFileName("/usr/lib/zoneinfo/"_L1 + QString::fromLocal8Bit(ianaId));
-            if (!tzif.open(QIODevice::ReadOnly)) {
-                // ianaId may be a POSIX rule, taken from $TZ or /etc/TZ
-                auto check = validatePosixRule(ianaId);
-                if (check.isValid) {
-                    ret.m_hasDst = check.hasDst;
-                    ret.m_posixRule = ianaId;
-                }
-                return ret;
-            }
+    } else if (!openZoneInfo(QString::fromLocal8Bit(ianaId), &tzif)) {
+        // ianaId may be a POSIX rule, taken from $TZ or /etc/TZ
+        auto check = validatePosixRule(ianaId);
+        if (check.isValid) {
+            ret.m_hasDst = check.hasDst;
+            ret.m_posixRule = ianaId;
+            return ret;
         }
     }
 
@@ -1332,7 +1350,8 @@ private:
     {
         // On most distros /etc/localtime is a symlink to a real file so extract
         // name from the path
-        const auto zoneinfo = "/zoneinfo/"_L1;
+        const QString tzdir = qEnvironmentVariable("TZDIR");
+        constexpr auto zoneinfo = "/zoneinfo/"_L1;
         QString path = QStringLiteral("/etc/localtime");
         long iteration = getSymloopMax();
         // Symlink may point to another symlink etc. before being under zoneinfo/
@@ -1340,8 +1359,14 @@ private:
         // symlink, like America/Montreal pointing to America/Toronto
         do {
             path = QFile::symLinkTarget(path);
-            int index = path.indexOf(zoneinfo);
-            if (index >= 0) // Found zoneinfo file; extract zone name from path:
+            // If it's a zoneinfo file, extract the zone name from its path:
+            int index = tzdir.isEmpty() ? -1 : path.indexOf(tzdir);
+            if (index >= 0) {
+                const auto tail = QStringView{ path }.sliced(index + tzdir.size()).toUtf8();
+                return tail.startsWith(u'/') ? tail.sliced(1) : tail;
+            }
+            index = path.indexOf(zoneinfo);
+            if (index >= 0)
                 return QStringView{ path }.sliced(index + zoneinfo.size()).toUtf8();
         } while (!path.isEmpty() && --iteration > 0);