From 9160cf6a070e8c18e2ecc764d1a957b3e37212b5 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Fri, 22 Jul 2022 09:11:16 -0700
Subject: [PATCH] QVariant: do allow non-default-constructible types

So long as you only ask us to copy it. Copying is mandatory, though.

I'll firm up the warning in a later commit, which may not get cherry-
picked as far back.

Fixes: QTBUG-105140
Change-Id: I3859764fed084846bcb0fffd170432abf65dc197
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit df0085d3a28005e84eb7688cc2575a121ba322aa)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/kernel/qvariant.cpp               |  2 +-
 .../corelib/kernel/qvariant/tst_qvariant.cpp  | 31 +++++++++++++++++--
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/corelib/kernel/qvariant.cpp b/src/corelib/kernel/qvariant.cpp
index a2711a48f85..94d062f6332 100644
--- a/src/corelib/kernel/qvariant.cpp
+++ b/src/corelib/kernel/qvariant.cpp
@@ -220,7 +220,7 @@ static void customConstruct(QVariant::Private *d, const void *copy)
         *d = QVariant::Private();
         return;
     }
-    if (!(iface->copyCtr && iface->defaultCtr)) {
+    if (!iface->copyCtr || (!copy && !iface->defaultCtr)) {
         // QVariant requires type to be copy and default constructible
         *d = QVariant::Private();
         qWarning("QVariant: Provided metatype does not support "
diff --git a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
index 240c25ae480..f20fd0cd878 100644
--- a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
+++ b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
@@ -289,6 +289,7 @@ private slots:
 
     void constructFromIncompatibleMetaType_data();
     void constructFromIncompatibleMetaType();
+    void copyNonDefaultConstructible();
 
 private:
     void dataStream_data(QDataStream::Version version);
@@ -5110,11 +5111,19 @@ void tst_QVariant::equalsWithoutMetaObject()
     QVERIFY(qobjectVariant != noMetaObjectVariant);
 }
 
-class NonDefaultConstructible
+struct NonDefaultConstructible
 {
-   NonDefaultConstructible(int ) {}
+   NonDefaultConstructible(int i) :i(i) {}
+   int i;
+   friend bool operator==(NonDefaultConstructible l, NonDefaultConstructible r)
+   { return l.i == r.i; }
 };
 
+template <> char *QTest::toString<NonDefaultConstructible>(const NonDefaultConstructible &ndc)
+{
+    return qstrdup('{' + QByteArray::number(ndc.i) + '}');
+}
+
 struct Indestructible
 {
     Indestructible() {}
@@ -5154,5 +5163,23 @@ void tst_QVariant::constructFromIncompatibleMetaType()
    QVERIFY(!QVariant(regular).convert(type));
 }
 
+void tst_QVariant::copyNonDefaultConstructible()
+{
+    NonDefaultConstructible ndc(42);
+    QVariant var(QMetaType::fromType<NonDefaultConstructible>(), &ndc);
+    QVERIFY(var.isDetached());
+    QCOMPARE(var.metaType(), QMetaType::fromType<NonDefaultConstructible>());
+    QVERIFY(var.constData() != &ndc);
+
+    // qvariant_cast<T> and QVariant::value<T> don't compile
+    QCOMPARE(*static_cast<const NonDefaultConstructible *>(var.constData()), ndc);
+
+    QVariant var2 = var;
+    var2.detach();      // force another copy
+    QVERIFY(var2.isDetached());
+    QVERIFY(var2.constData() != var.constData());
+    QCOMPARE(var2, var);
+}
+
 QTEST_MAIN(tst_QVariant)
 #include "tst_qvariant.moc"