11 files changed, 207 insertions, 8 deletions
diff --git a/tests/auto/gui/image/qicon/CMakeLists.txt b/tests/auto/gui/image/qicon/CMakeLists.txt
index c900c60d5b..93f75741c0 100644
--- a/tests/auto/gui/image/qicon/CMakeLists.txt
+++ b/tests/auto/gui/image/qicon/CMakeLists.txt
@@ -5,6 +5,12 @@
 ## tst_qicon Test:
 #####################################################################
 
+if(NOT QT_BUILD_STANDALONE_TESTS AND NOT QT_BUILDING_QT)
+    cmake_minimum_required(VERSION 3.16)
+    project(tst_qicon LANGUAGES CXX)
+    find_package(Qt6BuildInternals REQUIRED COMPONENTS STANDALONE_TEST)
+endif()
+
 # Collect test data
 file(GLOB_RECURSE test_data_glob
     RELATIVE ${CMAKE_CURRENT_SOURCE_DIR}
@@ -31,11 +37,14 @@ file(GLOB_RECURSE test_data_glob
     *.svgz)
 list(APPEND test_data ${test_data_glob})
 
+add_subdirectory(plugin)
+
 qt_internal_add_test(tst_qicon
     SOURCES
         tst_qicon.cpp
     LIBRARIES
         Qt::Gui
+        TestIconPlugin
     TESTDATA ${test_data}
 )
 
@@ -56,6 +65,10 @@ set(tst_qicon_resource_files
     "./icons/themeparent/index.theme"
     "./icons/themeparent/scalable/actions/address-book-new.svg"
     "./icons/themeparent/scalable/actions/appointment-new.svg"
+    "./icons/fallbacktheme/index.theme"
+    "./icons/fallbacktheme/16x16/edit-cut.png"
+    "./icons/hicolor/index.theme"
+    "./icons/hicolor/16x16/hicolor-icon.png"
     "./second_icons/testtheme/32x32/actions/appointment-new.png"
     "./styles/commonstyle/images/standardbutton-open-128.png"
     "./styles/commonstyle/images/standardbutton-open-16.png"
@@ -95,3 +108,5 @@ qt_internal_extend_target(tst_qicon CONDITION TARGET Qt::Widgets
     LIBRARIES
         Qt::Widgets
 )
+
+add_dependencies(tst_qicon TestIconPlugin)
diff --git a/tests/auto/gui/image/qicon/icons/fallbacktheme/16x16/edit-cut.png b/tests/auto/gui/image/qicon/icons/fallbacktheme/16x16/edit-cut.png
new file mode 100644
index 0000000000..661ef1ad03
--- /dev/null
+++ b/tests/auto/gui/image/qicon/icons/fallbacktheme/16x16/edit-cut.png
diff --git a/tests/auto/gui/image/qicon/icons/fallbacktheme/index.theme b/tests/auto/gui/image/qicon/icons/fallbacktheme/index.theme
new file mode 100644
index 0000000000..809d296669
--- /dev/null
+++ b/tests/auto/gui/image/qicon/icons/fallbacktheme/index.theme
@@ -0,0 +1,8 @@
+[Icon Theme]
+Name=fallbacktheme
+
+Directories=16x16
+
+[16x16]
+Size=16
+Type=Fixed
diff --git a/tests/auto/gui/image/qicon/icons/hicolor/16x16/hicolor-icon.png b/tests/auto/gui/image/qicon/icons/hicolor/16x16/hicolor-icon.png
new file mode 100644
index 0000000000..661ef1ad03
--- /dev/null
+++ b/tests/auto/gui/image/qicon/icons/hicolor/16x16/hicolor-icon.png
diff --git a/tests/auto/gui/image/qicon/icons/hicolor/index.theme b/tests/auto/gui/image/qicon/icons/hicolor/index.theme
new file mode 100644
index 0000000000..e5e5cef9b1
--- /dev/null
+++ b/tests/auto/gui/image/qicon/icons/hicolor/index.theme
@@ -0,0 +1,11 @@
+[Icon Theme]
+Name=hicolor
+
+# Provide a minimal hicolor theme, so that our hicolor fallback
+# lookup during testing will find that theme on all systems.
+
+Directories=16x16
+
+[16x16]
+Size=16
+Type=Fixed
diff --git a/tests/auto/gui/image/qicon/icons/testtheme/index.theme b/tests/auto/gui/image/qicon/icons/testtheme/index.theme
index e18736ab43..53664b14b2 100644
--- a/tests/auto/gui/image/qicon/icons/testtheme/index.theme
+++ b/tests/auto/gui/image/qicon/icons/testtheme/index.theme
@@ -1,7 +1,7 @@
 [Icon Theme]
 _Name=Test
 _Comment=Test Theme
-Inherits=crystalsvg, themeparent
+Inherits=themeparent
 Example=x-directory-normal
 
 # KDE Specific Stuff
diff --git a/tests/auto/gui/image/qicon/icons/themeparent/index.theme b/tests/auto/gui/image/qicon/icons/themeparent/index.theme
index e536a0bf2f..96267addd6 100644
--- a/tests/auto/gui/image/qicon/icons/themeparent/index.theme
+++ b/tests/auto/gui/image/qicon/icons/themeparent/index.theme
@@ -1,7 +1,6 @@
 [Icon Theme]
 _Name=Test
 _Comment=Test Theme
-Inherits=gnome,crystalsvg
 Example=x-directory-normal
 
 # KDE Specific Stuff
diff --git a/tests/auto/gui/image/qicon/plugin/CMakeLists.txt b/tests/auto/gui/image/qicon/plugin/CMakeLists.txt
new file mode 100644
index 0000000000..cae49b2df1
--- /dev/null
+++ b/tests/auto/gui/image/qicon/plugin/CMakeLists.txt
@@ -0,0 +1,20 @@
+# Copyright (C) 2024 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+#####################################################################
+## TestIconEngine Plugin:
+#####################################################################
+
+qt_internal_add_plugin(TestIconPlugin
+    STATIC
+    OUTPUT_NAME qtesticonplugin
+    OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}"
+    SKIP_INSTALL
+    PLUGIN_TYPE iconengines
+    DEFAULT_IF TRUE
+    SOURCES
+        main.cpp
+    LIBRARIES
+        Qt::Core
+        Qt::Gui
+)
diff --git a/tests/auto/gui/image/qicon/plugin/main.cpp b/tests/auto/gui/image/qicon/plugin/main.cpp
new file mode 100644
index 0000000000..58d9807142
--- /dev/null
+++ b/tests/auto/gui/image/qicon/plugin/main.cpp
@@ -0,0 +1,73 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
+
+#include <qiconengineplugin.h>
+#include <qiconengine.h>
+
+QT_BEGIN_NAMESPACE
+
+class TestIconPlugin : public QIconEnginePlugin
+{
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QIconEngineFactoryInterface" FILE "plugin.json")
+
+public:
+    QIconEngine *create(const QString &icon) override;
+};
+
+class TestIconEngine : public QIconEngine
+{
+public:
+    TestIconEngine(const QString &icon)
+        : m_iconName(QIcon::themeName() + "/" + icon)
+    {
+    }
+
+    ~TestIconEngine()
+    {}
+
+    QIconEngine *clone() const override
+    {
+        return new TestIconEngine(m_iconName);
+    }
+
+    QString key() const override
+    {
+        return QStringLiteral("TestIconEngine");
+    }
+
+    QString iconName() override
+    {
+        return m_iconName;
+    }
+
+    bool isNull() override
+    {
+        return m_iconName.isNull();
+    }
+
+    QList<QSize> availableSizes(QIcon::Mode, QIcon::State) override
+    {
+        return {{16, 16}, {48, 48}, {64, 64}};
+    }
+
+    void paint(QPainter *painter, const QRect &rect, QIcon::Mode mode, QIcon::State state) override
+    {
+        Q_UNUSED(painter);
+        Q_UNUSED(rect);
+        Q_UNUSED(mode);
+        Q_UNUSED(state);
+    }
+
+private:
+    const QString m_iconName;
+};
+
+QIconEngine *TestIconPlugin::create(const QString &icon)
+{
+    return new TestIconEngine(icon);
+}
+
+QT_END_NAMESPACE
+
+#include "main.moc"
diff --git a/tests/auto/gui/image/qicon/plugin/plugin.json b/tests/auto/gui/image/qicon/plugin/plugin.json
new file mode 100644
index 0000000000..96b59aa79e
--- /dev/null
+++ b/tests/auto/gui/image/qicon/plugin/plugin.json
@@ -0,0 +1,3 @@
+{
+    "Keys": [ "plugintheme", "SpecialTheme" ]
+}
diff --git a/tests/auto/gui/image/qicon/tst_qicon.cpp b/tests/auto/gui/image/qicon/tst_qicon.cpp
index ebb0f1e9d2..d95ee66fb6 100644
--- a/tests/auto/gui/image/qicon/tst_qicon.cpp
+++ b/tests/auto/gui/image/qicon/tst_qicon.cpp
@@ -1,5 +1,5 @@
 // Copyright (C) 2016 The Qt Company Ltd.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
 
 #include <QTest>
 #include <QImageReader>
@@ -41,12 +41,16 @@ private slots:
     void streamAvailableSizes();
     void fromTheme();
     void fromThemeCache();
+    void fromThemeConstant();
 
 #ifndef QT_NO_WIDGETS
     void task184901_badCache();
 #endif
     void task223279_inconsistentAddFile();
 
+    void themeFromPlugin_data();
+    void themeFromPlugin();
+
 private:
     bool haveImageFormat(QByteArray const&);
 
@@ -191,21 +195,21 @@ void tst_QIcon::isNull() {
     // test string constructor with empty string
     QIcon iconEmptyString = QIcon(QString());
     QVERIFY(iconEmptyString.isNull());
-    QVERIFY(!iconEmptyString.actualSize(QSize(32, 32)).isValid());;
+    QVERIFY(!iconEmptyString.actualSize(QSize(32, 32)).isValid());
 
     // test string constructor with non-existing file
     QIcon iconNoFile = QIcon("imagedoesnotexist");
-    QVERIFY(!iconNoFile.isNull());
+    QVERIFY(iconNoFile.isNull());
     QVERIFY(!iconNoFile.actualSize(QSize(32, 32)).isValid());
 
     // test string constructor with non-existing file with suffix
     QIcon iconNoFileSuffix = QIcon("imagedoesnotexist.png");
-    QVERIFY(!iconNoFileSuffix.isNull());
+    QVERIFY(iconNoFileSuffix.isNull());
     QVERIFY(!iconNoFileSuffix.actualSize(QSize(32, 32)).isValid());
 
     // test string constructor with existing file but unsupported format
     QIcon iconUnsupportedFormat = QIcon(m_sourceFileName);
-    QVERIFY(!iconUnsupportedFormat.isNull());
+    QVERIFY(iconUnsupportedFormat.isNull());
     QVERIFY(!iconUnsupportedFormat.actualSize(QSize(32, 32)).isValid());
 
     // test string constructor with existing file and supported format
@@ -552,6 +556,10 @@ void tst_QIcon::availableSizes()
 
 void tst_QIcon::name()
 {
+    const auto reset = qScopeGuard([]{
+        QIcon::setThemeName({});
+        QIcon::setThemeSearchPaths({});
+    });
     {
         // No name if icon does not come from a theme
         QIcon icon(":/image.png");
@@ -629,6 +637,7 @@ void tst_QIcon::task184901_badCache()
 
 void tst_QIcon::fromTheme()
 {
+    const bool abIconFromPlatform = !QIcon::fromTheme("address-book-new").isNull();
     QString firstSearchPath = QLatin1String(":/icons");
     QString secondSearchPath = QLatin1String(":/second_icons");
     QIcon::setThemeSearchPaths(QStringList() << firstSearchPath << secondSearchPath);
@@ -717,14 +726,44 @@ void tst_QIcon::fromTheme()
         QCOMPARE(i.availableSizes(), abIcon.availableSizes());
     }
 
+    // Setting or changing the fallback theme should invalidate earlier lookups.
+    // We can only test this if the system doesn't provide an icon, because once
+    // we got a valid icon, it will be cached, and even if we proxy to a different
+    // engine when a fallback theme is set, the cacheKey of the icon will be the
+    // same.
+    const QIcon editCut = QIcon::fromTheme("edit-cut");
+    if (editCut.isNull()) {
+        QIcon::setFallbackThemeName("fallbacktheme");
+        QVERIFY(!QIcon::fromTheme("edit-cut").isNull());
+    }
+
     // Make sure setting the theme name clears the state
     QIcon::setThemeName("");
     abIcon = QIcon::fromTheme("address-book-new");
-    QVERIFY(abIcon.isNull());
+    QCOMPARE_NE(abIcon.isNull(), abIconFromPlatform);
+
+    // Test fallback icon behavior for empty theme names.
+    // Can only reliably test this on systems that don't have a
+    // named system icon theme.
+    QIcon::setThemeName(""); // Reset user-theme
+    if (QIcon::themeName().isEmpty()) {
+        // Test icon from fallback theme even when theme name is empty
+        QIcon::setFallbackThemeName("fallbacktheme");
+        QVERIFY(!QIcon::fromTheme("edit-cut").isNull());
+
+        // Test icon from fallback path even when theme name is empty
+        fallbackIcon = QIcon::fromTheme("red");
+        QVERIFY(!fallbackIcon.isNull());
+        QVERIFY(QIcon::hasThemeIcon("red"));
+        QCOMPARE(fallbackIcon.availableSizes().size(), 1);
+    }
 
     // Passing a full path to fromTheme is not very useful, but should work anyway
     QIcon fullPathIcon = QIcon::fromTheme(m_pngImageFileName);
     QVERIFY(!fullPathIcon.isNull());
+
+    // Restore to system fallback theme
+    QIcon::setFallbackThemeName("");
 }
 
 static inline QString findGtkUpdateIconCache()
@@ -813,6 +852,11 @@ void tst_QIcon::fromThemeCache()
     QVERIFY(QIcon::fromTheme("notexist-fallback").isNull());
 }
 
+void tst_QIcon::fromThemeConstant()
+{
+    const QIcon icon = QIcon::fromTheme(QIcon::ThemeIcon::EditCut);
+}
+
 void tst_QIcon::task223279_inconsistentAddFile()
 {
     QIcon icon1;
@@ -831,6 +875,32 @@ void tst_QIcon::task223279_inconsistentAddFile()
     QCOMPARE(pm1.size(), pm2.size());
 }
 
+Q_IMPORT_PLUGIN(TestIconPlugin)
+
+void tst_QIcon::themeFromPlugin_data()
+{
+    QTest::addColumn<QString>("themeName");
+
+    QTest::addRow("plugintheme") << "plugintheme";
+    QTest::addRow("specialtheme") << "specialTheme"; // deliberately not matching case
+}
+
+void tst_QIcon::themeFromPlugin()
+{
+    QFETCH(const QString, themeName);
+    auto restoreTheme = qScopeGuard([oldTheme = QIcon::themeName()]{
+        QIcon::setThemeName(oldTheme);
+    });
+
+    QIcon icon = QIcon::fromTheme("icon1");
+    QVERIFY(icon.isNull());
+
+    QIcon::setThemeName(themeName);
+
+    icon = QIcon::fromTheme("icon1");
+    QVERIFY(!icon.isNull());
+    QCOMPARE(icon.name(), themeName + "/icon1");
+}
 
 QTEST_MAIN(tst_QIcon)
 #include "tst_qicon.moc"