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
Pick-to: 6.4
Change-Id: I2936db5933f4589fce45f47cf2f3224ed614d8c9
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 29 insertions, 2 deletions

diff --git a/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp b/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp
index 5842d7b3b1..94c04157f2 100644
--- a/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp
+++ b/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp
@@ -115,6 +115,7 @@ private slots:
     void compare_tostring();
     void compare_tostring_data();
     void compare_unknown();
+    void compare_textFromDebug();
     void compareQObjects();
     void compareQStringLists();
     void compareQStringLists_data();
@@ -324,10 +325,36 @@ void tst_Cmptest::compare_tostring()
     QCOMPARE(actual, expected);
 }
 
+struct UnknownType
+{
+    int value;
+    bool operator==(const UnknownType &rhs) const { return value == rhs.value; }
+};
+
 void tst_Cmptest::compare_unknown()
 {
-    std::string a("a");
-    std::string b("b");
+    UnknownType a{1};
+    UnknownType b{2};
+
+    QCOMPARE(a, b);
+}
+
+struct CustomType
+{
+    int value;
+    bool operator==(const CustomType &rhs) const { return value == rhs.value; }
+};
+
+QDebug operator<<(QDebug dbg, const CustomType &val)
+{
+    dbg << "QDebug stream: " << val.value;
+    return dbg;
+}
+
+void tst_Cmptest::compare_textFromDebug()
+{
+    CustomType a{0};
+    CustomType b{1};
 
     QCOMPARE(a, b);
 }