tst_QSpan: check QList<int> -> QSpan<const int> doesn't detach the fo…

…rmer

It does.

While std::span, does, too, and so users should be using
std::as_const(), it's quite simple to avoid for QSpan, so we'll fix it
in QSpan. This patch adds the reproducer.

Task-number: QTBUG-132133
Pick-to: 6.9 6.8
Change-Id: I2e416fb7344830cd5e0d945cce61491cd6f4a7a5
Reviewed-by: Giuseppe D'Angelo <[email protected]>
Reviewed-by: Thiago Macieira <[email protected]>

tests/auto/corelib/tools/qspan/tst_qspan.cpp

@@ -129,6 +129,8 @@ private Q_SLOTS:
     void fromQList() const;
     void fromInitList() const;
 
+    void constQSpansDontDetachQtContainers() const;
+
 private:
     template <typename T, std::size_t N, typename S, std::size_t M>
     void check_identical(QSpan<T, N> lhs, QSpan<S, M> rhs) const;
@@ -468,6 +470,32 @@ void tst_QSpan::fromQList() const
     from_variable_size_container_impl(li);
 }
 
+void tst_QSpan::constQSpansDontDetachQtContainers() const
+{
+    QList<int> li = {42, 84, 168, 336};
+
+    {
+        [[maybe_unused]] const QList copy = li;
+        QVERIFY(!li.isDetached());
+        [[maybe_unused]] QSpan<const int> cvspan = li; // should not detach (QTBUG-132133)
+        QEXPECT_FAIL("", "QTBUG-132133", Continue);
+        QVERIFY(!li.isDetached());
+        [[maybe_unused]] QSpan<int> mvspan = li; // this _has_ to detach, though
+        QVERIFY(li.isDetached());
+    }
+
+    // same check for fixed-size spans
+    {
+        [[maybe_unused]] const QList copy = li;
+        QVERIFY(!li.isDetached());
+        [[maybe_unused]] QSpan<const int, 4> cfspan = li; // should not detach (QTBUG-132133)
+        QEXPECT_FAIL("", "QTBUG-132133", Continue);
+        QVERIFY(!li.isDetached());
+        [[maybe_unused]] QSpan<int, 4> mfspan = li; // this _has_ to detach, though
+        QVERIFY(li.isDetached());
+    }
+}
+
 void tst_QSpan::fromInitList() const
 {
     from_variable_size_container_impl(std::initializer_list<int>{42, 84, 168, 336});