QFileSystemModel: cache the name filters regexps

In order to filter out file names based on the user's settings,
QFileSystemModel used to have a loop that tested if a given file
name matched one of the filters. The problem is that each filter
(a wildcard) was converted to a QRegularExpression _inside_ the loop.
This causes a quadratic behavior (number of files * number of filters).

Instead, build the regexps once when the filters are set (or the case
sensitivity is changed, as that affects the filtering), and simply
_use_ them in the loop.

Simplify and correct some related code as a drive by.

Done-with: Jean-Michaël Celerier
Fixes: QTBUG-95383
Change-Id: I6bc336364c145bb05793a8f867545d7715d35832
Reviewed-by: Samuel Gaist <samuel.gaist@idiap.ch>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
(cherry picked from commit 07057188e3e42246cf006b43963d0bdcdaa159f5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/itemmodels/qfilesystemmodel.cpp

@@ -1594,9 +1594,11 @@ void QFileSystemModel::setFilter(QDir::Filters filters)
     Q_D(QFileSystemModel);
     if (d->filters == filters)
         return;
+    const bool changingCaseSensitivity =
+        filters.testFlag(QDir::CaseSensitive) != d->filters.testFlag(QDir::CaseSensitive);
     d->filters = filters;
-    // CaseSensitivity might have changed
+    if (changingCaseSensitivity)
-    setNameFilters(nameFilters());
+        d->rebuildNameFilterRegexps();
     d->forceSort = true;
     d->delayedSort();
 }
@@ -1693,7 +1695,6 @@ bool QFileSystemModel::nameFilterDisables() const
 */
 void QFileSystemModel::setNameFilters(const QStringList &filters)
 {
-    // Prep the regexp's ahead of time
 #if QT_CONFIG(regularexpression)
     Q_D(QFileSystemModel);
 
@@ -1716,6 +1717,7 @@ void QFileSystemModel::setNameFilters(const QStringList &filters)
     }
 
     d->nameFilters = filters;
+    d->rebuildNameFilterRegexps();
     d->forceSort = true;
     d->delayedSort();
 #else
@@ -2152,15 +2154,13 @@ bool QFileSystemModelPrivate::passNameFilters(const QFileSystemNode *node) const
 
     // Check the name regularexpression filters
     if (!(node->isDir() && (filters & QDir::AllDirs))) {
-        auto cs = (filters & QDir::CaseSensitive) ? Qt::CaseSensitive : Qt::CaseInsensitive;
+        const auto matchesNodeFileName = [node](const QRegularExpression &re)
-
+        {
-        for (const auto &nameFilter : nameFilters) {
+            return node->fileName.contains(re);
-            auto rx = QRegularExpression::fromWildcard(nameFilter, cs);
+        };
-            QRegularExpressionMatch match = rx.match(node->fileName);
+        return std::any_of(nameFiltersRegexps.begin(),
-            if (match.hasMatch())
+                           nameFiltersRegexps.end(),
-                return true;
+                           matchesNodeFileName);
-        }
-        return false;
     }
 #else
     Q_UNUSED(node);
@@ -2168,6 +2168,23 @@ bool QFileSystemModelPrivate::passNameFilters(const QFileSystemNode *node) const
     return true;
 }
 
+#if QT_CONFIG(regularexpression)
+void QFileSystemModelPrivate::rebuildNameFilterRegexps()
+{
+    nameFiltersRegexps.clear();
+    nameFiltersRegexps.reserve(nameFilters.size());
+    const auto cs = (filters & QDir::CaseSensitive) ? Qt::CaseSensitive : Qt::CaseInsensitive;
+    const auto convertWildcardToRegexp = [cs](const QString &nameFilter)
+    {
+        return QRegularExpression::fromWildcard(nameFilter, cs);
+    };
+    std::transform(nameFilters.constBegin(),
+                   nameFilters.constEnd(),
+                   std::back_inserter(nameFiltersRegexps),
+                   convertWildcardToRegexp);
+}
+#endif
+
 QT_END_NAMESPACE
 
 #include "moc_qfilesystemmodel.cpp"

src/gui/itemmodels/qfilesystemmodel_p.h

@@ -64,6 +64,8 @@
 #include <qtimer.h>
 #include <qhash.h>
 
+#include <vector>
+
 QT_REQUIRE_CONFIG(filesystemmodel);
 
 QT_BEGIN_NAMESPACE
@@ -291,6 +293,8 @@ public:
     QHash<const QFileSystemNode*, bool> bypassFilters;
 #if QT_CONFIG(regularexpression)
     QStringList nameFilters;
+    std::vector<QRegularExpression> nameFiltersRegexps;
+    void rebuildNameFilterRegexps();
 #endif
     QHash<QString, QString> resolvedSymLinks;