QFileSystemModel: add lastModified() overload that takes a QTimeZone

This is useful when sorting by time and using QTimeZone::UTC, since
native filesystem API uses UTC, that means less conversions, which is
potentially faster.

Use UTC internally except for strings that are going to be shown in a
GUI to the user, these should be in QTimeZone::LocalTime.

[ChangeLog][QtGui][QFileSystemModel] Added lastModified() overload that
takes a QTimeZone, this is useful when e.g. comparing file timestamps
and all that's needed is time in UTC (this is faster as no time zone
conversions is required). QTimeZone::UTC is used internally when sorting
by time (using the sort() function), which should ideally make it
faster too.

Task-number: QTBUG-100349
Change-Id: I0e58f8eb7856b8da7d55db86ddd2c009ff83d970
Reviewed-by: Kai Köhne <kai.koehne@qt.io>

src/gui/itemmodels/qfileinfogatherer_p.h

@@ -51,7 +51,7 @@ public:
        return mFileInfo == fileInfo.mFileInfo
        && displayType == fileInfo.displayType
        && permissions() == fileInfo.permissions()
-       && lastModified() == fileInfo.lastModified();
+       && lastModified(QTimeZone::UTC) == fileInfo.lastModified(QTimeZone::UTC);
     }
 
 #ifndef QT_NO_FSFILEENGINE
@@ -95,8 +95,8 @@ public:
         return mFileInfo;
     }
 
-    QDateTime lastModified() const {
+    QDateTime lastModified(const QTimeZone &tz) const {
-        return mFileInfo.lastModified();
+        return mFileInfo.lastModified(tz);
     }
 
     qint64 size() const {

src/gui/itemmodels/qfilesystemmodel.cpp

@@ -529,14 +529,38 @@ QString QFileSystemModel::type(const QModelIndex &index) const
 }
 
 /*!
-    Returns the date and time when \a index was last modified.
+    Returns the date and time (in local time) when \a index was last modified.
+
+    This is an overloaded function, equivalent to calling:
+    \code
+    lastModified(index, QTimeZone::LocalTime);
+    \endcode
+
+    If \a index is invalid, a default constructed QDateTime is returned.
  */
 QDateTime QFileSystemModel::lastModified(const QModelIndex &index) const
+{
+    return lastModified(index, QTimeZone::LocalTime);
+}
+
+/*!
+    \since 6.6
+    Returns the date and time, in the time zone \a tz, when
+    \a index was last modified.
+
+    Typical arguments for \a tz are \c QTimeZone::UTC or \c QTimeZone::LocalTime.
+    UTC does not require any conversion from the time returned by the native file
+    system API, therefore getting the time in UTC is potentially faster. LocalTime
+    is typically chosen if the time is shown to the user.
+
+    If \a index is invalid, a default constructed QDateTime is returned.
+ */
+QDateTime QFileSystemModel::lastModified(const QModelIndex &index, const QTimeZone &tz) const
 {
     Q_D(const QFileSystemModel);
     if (!index.isValid())
         return QDateTime();
-    return d->node(index)->lastModified();
+    return d->node(index)->lastModified(tz);
 }
 
 /*!
@@ -765,7 +789,7 @@ QString QFileSystemModelPrivate::time(const QModelIndex &index) const
     if (!index.isValid())
         return QString();
 #if QT_CONFIG(datestring)
-    return QLocale::system().toString(node(index)->lastModified(), QLocale::ShortFormat);
+    return QLocale::system().toString(node(index)->lastModified(QTimeZone::LocalTime), QLocale::ShortFormat);
 #else
     Q_UNUSED(index);
     return QString();
@@ -1027,10 +1051,12 @@ public:
         }
         case 3:
         {
-            if (l->lastModified() == r->lastModified())
+            const QDateTime left = l->lastModified(QTimeZone::UTC);
+            const QDateTime right = r->lastModified(QTimeZone::UTC);
+            if (left == right)
                 return naturalCompare.compare(l->fileName, r->fileName) < 0;
 
-            return l->lastModified() < r->lastModified();
+            return left < right;
         }
         }
         Q_ASSERT(false);

src/gui/itemmodels/qfilesystemmodel.h

@@ -113,7 +113,10 @@ public:
     bool isDir(const QModelIndex &index) const;
     qint64 size(const QModelIndex &index) const;
     QString type(const QModelIndex &index) const;
+
+    // ### Qt7 merge the two overloads, with tz QTimeZone::LocalTime
     QDateTime lastModified(const QModelIndex &index) const;
+    QDateTime lastModified(const QModelIndex &index, const QTimeZone &tz) const;
 
     QModelIndex mkdir(const QModelIndex &parent, const QString &name);
     bool rmdir(const QModelIndex &index);

src/gui/itemmodels/qfilesystemmodel_p.h

@@ -84,7 +84,7 @@ public:
 
         inline qint64 size() const { if (info && !info->isDir()) return info->size(); return 0; }
         inline QString type() const { if (info) return info->displayType; return QLatin1StringView(""); }
-        inline QDateTime lastModified() const { if (info) return info->lastModified(); return QDateTime(); }
+        inline QDateTime lastModified(const QTimeZone &tz) const { return info ? info->lastModified(tz) : QDateTime(); }
         inline QFile::Permissions permissions() const { if (info) return info->permissions(); return { }; }
         inline bool isReadable() const { return ((permissions() & QFile::ReadUser) != 0); }
         inline bool isWritable() const { return ((permissions() & QFile::WriteUser) != 0); }