QFactoryLoader: add setExtraSearchPath() (for QPA plugins' use)

This is added specifically for the QPA platform and theme plugins, to
honor the QT_QPA_PLATFORM_PLUGIN_PATH environment variable and the
(inadvisable) -platformpluginpath command-line argument.

This removes the last QFactoryLoader used with an empty path (also the
only two that could be reached), which were causing a scan of the
application's binary directory whenever the platform plugin path was
set. In case of applications installed to /usr/bin, the entire /usr/bin
was scanned, which can be qualified as "not good".

Fixes: QTBUG-97950
Pick-to: 6.3
Change-Id: Ice04365c72984d07a64dfffd16b47fe1d22f26d3
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

4 files changed, 40 insertions, 72 deletions

diff --git a/src/corelib/plugin/qfactoryloader.cpp b/src/corelib/plugin/qfactoryloader.cpp
index 19d858bf8d..0342f1924a 100644
--- a/src/corelib/plugin/qfactoryloader.cpp
+++ b/src/corelib/plugin/qfactoryloader.cpp
@@ -1,7 +1,7 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
-** Copyright (C) 2018 Intel Corporation.
+** Copyright (C) 2021 The Qt Company Ltd.
+** Copyright (C) 2022 Intel Corporation.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -140,6 +140,7 @@ public:
     QList<QLibraryPrivate*> libraryList;
     QMap<QString,QLibraryPrivate*> keyMap;
     QString suffix;
+    QString extraSearchPath;
     Qt::CaseSensitivity cs;
 
     void updateSinglePath(const QString &pluginDir);
@@ -276,6 +277,8 @@ void QFactoryLoader::update()
 
         d->updateSinglePath(path);
     }
+    if (!d->extraSearchPath.isEmpty())
+        d->updateSinglePath(d->extraSearchPath);
 #else
     Q_D(QFactoryLoader);
     qCDebug(lcFactoryLoader) << "ignoring" << d->iid
@@ -314,6 +317,9 @@ QFactoryLoader::QFactoryLoader(const char *iid,
                                Qt::CaseSensitivity cs)
     : QObject(*new QFactoryLoaderPrivate)
 {
+    Q_ASSERT_X(suffix.startsWith(u'/'), "QFactoryLoader",
+               "For historical reasons, the suffix must start with '/' (and it can't be empty)");
+
     moveToThread(QCoreApplicationPrivate::mainThread());
     Q_D(QFactoryLoader);
     d->iid = iid;
@@ -334,6 +340,30 @@ QFactoryLoader::QFactoryLoader(const char *iid,
 #endif
 }
 
+void QFactoryLoader::setExtraSearchPath(const QString &path)
+{
+#if QT_CONFIG(library)
+    Q_D(QFactoryLoader);
+    if (d->extraSearchPath == path)
+        return;             // nothing to do
+
+    QMutexLocker locker(qt_factoryloader_mutex());
+    QString oldPath = qExchange(d->extraSearchPath, path);
+    if (oldPath.isEmpty()) {
+        // easy case, just update this directory
+        d->updateSinglePath(d->extraSearchPath);
+    } else {
+        // must re-scan everything
+        d->loadedPaths.clear();
+        d->libraryList.clear();
+        d->keyMap.clear();
+        update();
+    }
+#else
+    Q_UNUSED(path);
+#endif
+}
+
 QFactoryLoader::MetaDataList QFactoryLoader::metaData() const
 {
     Q_D(const QFactoryLoader);
diff --git a/src/corelib/plugin/qfactoryloader_p.h b/src/corelib/plugin/qfactoryloader_p.h
index f7033d144f..633cf0a916 100644
--- a/src/corelib/plugin/qfactoryloader_p.h
+++ b/src/corelib/plugin/qfactoryloader_p.h
@@ -1,7 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2017 The Qt Company Ltd.
-** Copyright (C) 2021 Intel Corporation.
+** Copyright (C) 2022 Intel Corporation.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -115,6 +115,7 @@ public:
 #endif // Q_OS_UNIX && !Q_OS_MAC
 #endif // QT_CONFIG(library)
 
+    void setExtraSearchPath(const QString &path);
     QMultiMap<int, QString> keyMap() const;
     int indexOf(const QString &needle) const;
 
diff --git a/src/gui/kernel/qplatformintegrationfactory.cpp b/src/gui/kernel/qplatformintegrationfactory.cpp
index 3fcf9014a7..22cdf2ccf8 100644
--- a/src/gui/kernel/qplatformintegrationfactory.cpp
+++ b/src/gui/kernel/qplatformintegrationfactory.cpp
@@ -51,23 +51,9 @@ QT_BEGIN_NAMESPACE
 Q_GLOBAL_STATIC_WITH_ARGS(QFactoryLoader, loader,
     (QPlatformIntegrationFactoryInterface_iid, QLatin1String("/platforms"), Qt::CaseInsensitive))
 
-#if QT_CONFIG(library)
-Q_GLOBAL_STATIC_WITH_ARGS(QFactoryLoader, directLoader,
-                          (QPlatformIntegrationFactoryInterface_iid, QLatin1String(""), Qt::CaseInsensitive))
-#endif // QT_CONFIG(library)
-
 QPlatformIntegration *QPlatformIntegrationFactory::create(const QString &platform, const QStringList &paramList, int &argc, char **argv, const QString &platformPluginPath)
 {
-#if QT_CONFIG(library)
-    // Try loading the plugin from platformPluginPath first:
-    if (!platformPluginPath.isEmpty()) {
-        QCoreApplication::addLibraryPath(platformPluginPath);
-        if (QPlatformIntegration *ret = qLoadPlugin<QPlatformIntegration, QPlatformIntegrationPlugin>(directLoader(), platform, paramList, argc, argv))
-            return ret;
-    }
-#else
-    Q_UNUSED(platformPluginPath);
-#endif
+    loader->setExtraSearchPath(platformPluginPath);
     return qLoadPlugin<QPlatformIntegration, QPlatformIntegrationPlugin>(loader(), platform, paramList, argc, argv);
 }
 
@@ -80,25 +66,8 @@ QPlatformIntegration *QPlatformIntegrationFactory::create(const QString &platfor
 
 QStringList QPlatformIntegrationFactory::keys(const QString &platformPluginPath)
 {
-    QStringList list;
-#if QT_CONFIG(library)
-    if (!platformPluginPath.isEmpty()) {
-        QCoreApplication::addLibraryPath(platformPluginPath);
-        list = directLoader()->keyMap().values();
-        if (!list.isEmpty()) {
-            const QString postFix = QLatin1String(" (from ")
-                                    + QDir::toNativeSeparators(platformPluginPath)
-                                    + QLatin1Char(')');
-            const QStringList::iterator end = list.end();
-            for (QStringList::iterator it = list.begin(); it != end; ++it)
-                (*it).append(postFix);
-        }
-    }
-#else
-    Q_UNUSED(platformPluginPath);
-#endif
-    list.append(loader()->keyMap().values());
-    return list;
+    loader->setExtraSearchPath(platformPluginPath);
+    return loader->keyMap().values();
 }
 
 QT_END_NAMESPACE
diff --git a/src/gui/kernel/qplatformthemefactory.cpp b/src/gui/kernel/qplatformthemefactory.cpp
index 447d385abe..0d7163cdd4 100644
--- a/src/gui/kernel/qplatformthemefactory.cpp
+++ b/src/gui/kernel/qplatformthemefactory.cpp
@@ -51,25 +51,11 @@ QT_BEGIN_NAMESPACE
 Q_GLOBAL_STATIC_WITH_ARGS(QFactoryLoader, loader,
     (QPlatformThemeFactoryInterface_iid, QLatin1String("/platformthemes"), Qt::CaseInsensitive))
 
-#if QT_CONFIG(library)
-Q_GLOBAL_STATIC_WITH_ARGS(QFactoryLoader, directLoader,
-                          (QPlatformThemeFactoryInterface_iid, QLatin1String(""), Qt::CaseInsensitive))
-#endif
-
 QPlatformTheme *QPlatformThemeFactory::create(const QString& key, const QString &platformPluginPath)
 {
     QStringList paramList = key.split(QLatin1Char(':'));
     const QString platform = paramList.takeFirst().toLower();
-#if QT_CONFIG(library)
-    // Try loading the plugin from platformPluginPath first:
-    if (!platformPluginPath.isEmpty()) {
-        QCoreApplication::addLibraryPath(platformPluginPath);
-        if (QPlatformTheme *ret = qLoadPlugin<QPlatformTheme, QPlatformThemePlugin>(directLoader(), platform, paramList))
-            return ret;
-    }
-#else
-    Q_UNUSED(platformPluginPath);
-#endif
+    loader->setExtraSearchPath(platformPluginPath);
     return qLoadPlugin<QPlatformTheme, QPlatformThemePlugin>(loader(), platform, paramList);
 }
 
@@ -81,26 +67,8 @@ QPlatformTheme *QPlatformThemeFactory::create(const QString& key, const QString
 */
 QStringList QPlatformThemeFactory::keys(const QString &platformPluginPath)
 {
-    QStringList list;
-
-#if QT_CONFIG(library)
-    if (!platformPluginPath.isEmpty()) {
-        QCoreApplication::addLibraryPath(platformPluginPath);
-        list += directLoader()->keyMap().values();
-        if (!list.isEmpty()) {
-            const QString postFix = QLatin1String(" (from ")
-                    + QDir::toNativeSeparators(platformPluginPath)
-                    + QLatin1Char(')');
-            const QStringList::iterator end = list.end();
-            for (QStringList::iterator it = list.begin(); it != end; ++it)
-                (*it).append(postFix);
-        }
-    }
-#else
-    Q_UNUSED(platformPluginPath);
-#endif
-    list += loader()->keyMap().values();
-    return list;
+    loader->setExtraSearchPath(platformPluginPath);
+    return loader->keyMap().values();
 }
 
 QT_END_NAMESPACE