Use debug stream in QTest::toString's default fallback if possible

For built-in types, this is a compile-time assert - we should not have
any types in Qt for which we have neither debug streaming nor a
QTest::toString specialization implemented. A build of most of Qt
submodules passes with this change, after minor modifications to some
tests. We cannot declare QSizeHint::Policy as a metatype after the
QMetaType has already been instantiated for it, and the QDebug stream
operator for QElaspedTimer needs to be correctly declared within the
namespace.

Add a self-test function for a custom type, and update reference files
of the self-test.

Task-number: QTBUG-104867
Change-Id: I2936db5933f4589fce45f47cf2f3224ed614d8c9
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 92e696b4bad52c40c6cdc1c5bf7c0c0ea8a2b283)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/testlib/qtestcase.h b/src/testlib/qtestcase.h
index 0412f872f7..d8ad48d2c0 100644
--- a/src/testlib/qtestcase.h
+++ b/src/testlib/qtestcase.h
@@ -307,9 +307,18 @@ namespace QTest
         return qstrdup(QByteArray::number(static_cast<std::underlying_type_t<T>>(e)).constData());
     }
 
-    template <typename T> // Fallback
-    inline typename std::enable_if<!QtPrivate::IsQEnumHelper<T>::Value && !std::is_enum_v<T>, char*>::type toString(const T &)
+    template <typename T> // Fallback; for built-in types debug streaming must be possible
+    inline typename std::enable_if<!QtPrivate::IsQEnumHelper<T>::Value && !std::is_enum_v<T>, char *>::type toString(const T &t)
     {
+#ifndef QT_NO_DEBUG_STREAM
+        if constexpr (QTypeTraits::has_ostream_operator_v<QDebug, T>) {
+            return qstrdup(QDebug::toString(t).toUtf8().constData());
+        } else {
+            static_assert(!QMetaTypeId2<T>::IsBuiltIn,
+                        "Built-in type must implement debug streaming operator "
+                        "or provide QTest::toString specialization");
+        }
+#endif
         return nullptr;
     }