From 657a18c7faac28d7025350834dc7686e689ac358 Mon Sep 17 00:00:00 2001
From: Ulf Hermann <ulf.hermann@qt.io>
Date: Wed, 12 Jan 2022 17:26:11 +0100
Subject: QMetaType: Allow conversion of derived gadget types to their base
 types

A derived gadget has an is-a relationship with its base type. It
should be convertible. In fact, canConvert() already tells us it is.

Change-Id: I71a5ac9afd78e88adb23b4d0e757f34077f63207
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
---
 tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h    | 16 ++++++++++++++++
 tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp | 16 ++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

(limited to 'tests/auto/corelib/kernel')

diff --git a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h
index 65fe3859f0..b126b86475 100644
--- a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h
+++ b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h
@@ -217,6 +217,22 @@ struct CustomEqualsOnlyType
 static_assert(QTypeTraits::has_operator_equal_v<CustomEqualsOnlyType>);
 static_assert(!QTypeTraits::has_operator_less_than_v<CustomEqualsOnlyType>);
 
+struct BaseGadgetType
+{
+    Q_GADGET
+public:
+    explicit BaseGadgetType(QVariant foo = QVariant()) : m_foo(std::move(foo)) {}
+    QVariant m_foo;
+};
+
+struct DerivedGadgetType : public BaseGadgetType
+{
+    Q_GADGET
+public:
+    explicit DerivedGadgetType(QVariant foo = QVariant()) : BaseGadgetType(std::move(foo)) {}
+    int bar = 25;
+};
+
 Q_DECLARE_METATYPE(CustomConvertibleType);
 Q_DECLARE_METATYPE(CustomConvertibleType2);
 Q_DECLARE_METATYPE(CustomDebugStreamableType);
diff --git a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp
index 8567288c8b..025353d9c0 100644
--- a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp
+++ b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp
@@ -164,6 +164,7 @@ void tst_QMetaType::convertCustomType_data()
     QTest::addColumn<QLineF>("testQLineF");
     QTest::addColumn<QChar>("testQChar");
     QTest::addColumn<CustomConvertibleType>("testCustom");
+    QTest::addColumn<DerivedGadgetType>("testDerived");
 
     QTest::newRow("default") << true
                              << QString::fromLatin1("string") << true << 15
@@ -171,14 +172,16 @@ void tst_QMetaType::convertCustomType_data()
                              << QRectF(1.4, 1.9, 10.9, 40.2) << QPoint(12, 34)
                              << QPointF(9.2, 2.7) << QSize(4, 9) << QSizeF(3.3, 9.8)
                              << QLine(3, 9, 29, 4) << QLineF(38.9, 28.9, 102.3, 0.0)
-                             << QChar('Q') << CustomConvertibleType(QString::fromLatin1("test"));
+                             << QChar('Q') << CustomConvertibleType(QString::fromLatin1("test"))
+                             << DerivedGadgetType(QString::fromLatin1("test"));
     QTest::newRow("not ok") << false
                             << QString::fromLatin1("string") << true << 15
                             << double(3.14) << float(3.6) << QRect(1, 2, 3, 4)
                             << QRectF(1.4, 1.9, 10.9, 40.2) << QPoint(12, 34)
                             << QPointF(9.2, 2.7) << QSize(4, 9) << QSizeF(3.3, 9.8)
                             << QLine(3, 9, 29, 4) << QLineF()
-                            << QChar('Q') << CustomConvertibleType(42);
+                            << QChar('Q') << CustomConvertibleType(42)
+                            << DerivedGadgetType(42);
 }
 
 void tst_QMetaType::convertCustomType()
@@ -276,6 +279,15 @@ void tst_QMetaType::convertCustomType()
     v = QVariant::fromValue(testCustom);
     QVERIFY(v.canConvert(::qMetaTypeId<CustomConvertibleType2>()));
     QCOMPARE(v.value<CustomConvertibleType2>().m_foo, testCustom.m_foo);
+
+    QFETCH(DerivedGadgetType, testDerived);
+    v = QVariant::fromValue(testDerived);
+    QCOMPARE(v.metaType(), QMetaType::fromType<DerivedGadgetType>());
+    QCOMPARE(v.value<DerivedGadgetType>().m_foo, testDerived.m_foo);
+    QVERIFY(v.canConvert(QMetaType::fromType<BaseGadgetType>()));
+    QVERIFY(v.convert(QMetaType::fromType<BaseGadgetType>()));
+    QCOMPARE(v.metaType(), QMetaType::fromType<BaseGadgetType>());
+    QCOMPARE(v.value<BaseGadgetType>().m_foo, testDerived.m_foo);
 }
 
 void tst_QMetaType::convertConstNonConst()
-- 
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