QMetaType: fix typenameHelper() for types in the QtPrivate namespace

GCC at some point decided that it wouldn't include the full namespace
expansion in __PRETTY_FUNCTION__ for any type that is in the same
namespace as the template function being expanded (that is, the
QtPrivate) namespace. I don't know how long this behavior has been in
place, but it can be seen with GCC 13, where the expansion of that macro
inside QtPrivate::typenameHelper<QtPrivate::ModelIndex>() is:

 constexpr auto QtPrivate::typenameHelper() [with T = ModelIndex]

This can be easily worked around by using a different namespace.

Fixes: QTBUG-119650
Pick-to: 6.6 6.5 6.2
Change-Id: Ica7a43f6147b49c187ccfffd179df309e43a70cb
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 24 insertions, 5 deletions

diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index 02ecaf9831..5528c2f459 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -2235,6 +2235,7 @@ struct is_std_pair<std::pair<T1_, T2_>> : std::true_type {
     using T2 = T2_;
 };
 
+namespace TypeNameHelper {
 template<typename T>
 constexpr auto typenameHelper()
 {
@@ -2276,15 +2277,15 @@ constexpr auto typenameHelper()
             QT_STRINGIFY(QT_NAMESPACE) "::"
 #endif
 #if defined(Q_CC_MSVC) && defined(Q_CC_CLANG)
-            "auto __cdecl QtPrivate::typenameHelper(void) [T = "
+            "auto __cdecl QtPrivate::TypeNameHelper::typenameHelper(void) [T = "
 #elif defined(Q_CC_MSVC)
-            "auto __cdecl QtPrivate::typenameHelper<"
+            "auto __cdecl QtPrivate::TypeNameHelper::typenameHelper<"
 #elif defined(Q_CC_CLANG)
-            "auto QtPrivate::typenameHelper() [T = "
+            "auto QtPrivate::TypeNameHelper::typenameHelper() [T = "
 #elif defined(Q_CC_GHS)
-            "auto QtPrivate::typenameHelper<T>()[with T="
+            "auto QtPrivate::TypeNameHelper::typenameHelper<T>()[with T="
 #else
-            "constexpr auto QtPrivate::typenameHelper() [with T = "
+            "constexpr auto QtPrivate::TypeNameHelper::typenameHelper() [with T = "
 #endif
             ) - 1;
 #if defined(Q_CC_MSVC) && !defined(Q_CC_CLANG)
@@ -2310,6 +2311,8 @@ constexpr auto typenameHelper()
         return result;
     }
 }
+} // namespace TypeNameHelper
+using TypeNameHelper::typenameHelper;
 
 template<typename T, typename = void>
 struct BuiltinMetaType : std::integral_constant<int, 0>
diff --git a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h
index 3afb494368..fb001f6a3a 100644
--- a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h
+++ b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.h
@@ -120,6 +120,7 @@ private slots:
     void typesWithInaccessibleDTors();
     void voidIsNotUnknown();
     void typeNameNormalization();
+    void typeNameInQtPrivate();
 
     // Tests for deprecated APIs
 #if QT_DEPRECATED_SINCE(6, 0)
diff --git a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp
index c0650c7b1a..bde4e19907 100644
--- a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp
+++ b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype2.cpp
@@ -640,6 +640,21 @@ void tst_QMetaType::typeNameNormalization()
     }
 }
 
+QT_BEGIN_NAMESPACE
+namespace QtPrivate { struct tst_QMetaType_TestType {}; }
+QT_END_NAMESPACE
+
+void tst_QMetaType::typeNameInQtPrivate()
+{
+    using T = QT_PREPEND_NAMESPACE(QtPrivate::tst_QMetaType_TestType);
+
+    // some compilers (GCC) are known to suppress the namespace prefix if the
+    // type and the function where it is expanded on are on the same namespace
+    static constexpr char expectedName[] = "QtPrivate::tst_QMetaType_TestType";
+    QMetaType mt = QMetaType::fromType<T>();
+    QCOMPARE(mt.name(), expectedName);
+}
+
 #if QT_DEPRECATED_SINCE(6, 0)
 void tst_QMetaType::testDeprecatedGetters()
 {