QMetaType & moc: remove the pair type from qTryMetaTypeInterfaceForType()

We can detect whether the intent is to require completeness by having
Unique = void. This simplifies QtMocHelpers as well, removing one more
class that needed to be instantiated for each metatype.

Change-Id: I3a256568bb6ce1754399fffd6f61144d0a3e8deb
Reviewed-by: Fabian Kosmale <[email protected]>

4 files changed, 25 insertions, 44 deletions

diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index f379803e4a4..97fdf8b4ef3 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -2617,13 +2617,6 @@ struct QRemovePointerLike<Pointer<T>> \
 QT_FOR_EACH_AUTOMATIC_TEMPLATE_SMART_POINTER(Q_REMOVE_POINTER_LIKE_IMPL)
 #undef Q_REMOVE_POINTER_LIKE_IMPL
 
-template<typename T, typename ForceComplete_>
-struct TypeAndForceComplete
-{
-    using type = T;
-    using ForceComplete = ForceComplete_;
-};
-
 template<typename T>
 constexpr const QMetaTypeInterface *qMetaTypeInterfaceForType()
 {
@@ -2632,18 +2625,21 @@ constexpr const QMetaTypeInterface *qMetaTypeInterfaceForType()
     return &QMetaTypeInterfaceWrapper<Ty>::metaType;
 }
 
-template<typename Unique, typename TypeCompletePair>
+// Relaxed vesion of the above, used by moc-generated code to create the
+// metatype array without requiring types to be complete and allowing
+// references. Unique is passed to is_complete and must be a different unique
+// type; if it is void, this function is equal to qMetaTypeInterfaceForType()
+// above.
+template<typename Unique, typename T>
 constexpr const QMetaTypeInterface *qTryMetaTypeInterfaceForType()
 {
-    using T = typename TypeCompletePair::type;
-    using ForceComplete = typename TypeCompletePair::ForceComplete;
     using Ty = typename MetatypeDecay<T>::type;
     using Tz = typename QRemovePointerLike<Ty>::type;
 
     if constexpr (std::is_void_v<Tz>) {
         // early out to avoid expanding the rest of the templates
         return &QMetaTypeInterfaceWrapper<Ty>::metaType;
-    } else if constexpr (ForceComplete::value) {
+    } else if constexpr (std::is_void_v<Unique>) {
         checkTypeIsSuitableForMetaType<Ty>();
         return &QMetaTypeInterfaceWrapper<Ty>::metaType;
     } else if constexpr (std::is_reference_v<Tz>) {
diff --git a/src/corelib/kernel/qtmochelpers.h b/src/corelib/kernel/qtmochelpers.h
index 588ae86d663..3099389b872 100644
--- a/src/corelib/kernel/qtmochelpers.h
+++ b/src/corelib/kernel/qtmochelpers.h
@@ -127,7 +127,6 @@ template <typename Prop, typename Value> inline bool setProperty(Prop &property,
 }
 
 struct NoType {};
-template <typename T> struct ForceCompleteMetaTypes {};
 
 namespace detail {
 template<typename Enum> constexpr int payloadSizeForEnum()
@@ -150,30 +149,15 @@ template <uint H, uint P> struct UintDataBlock
 
 // By default, we allow metatypes for incomplete types to be stored in the
 // metatype array, but we provide a way to require them to be complete by using
-// ForceCompleteMetaTypes in either the Unique type (used by moc if
-// --require-complete-types is passed or some internal heuristic for QML
-// matches) or in the type itself, used below for properties and enums.
-template <typename T> struct TypeMustBeComplete : std::false_type {};
-template <typename T> struct TypeMustBeComplete<ForceCompleteMetaTypes<T>> : std::true_type {};
-// template <> struct TypeMustBeComplete<void> : std::true_type {};
-
-template <typename Unique, typename T, typename RequireComplete = TypeMustBeComplete<Unique>>
-struct TryMetaTypeInterfaceForType
-{
-    static constexpr const QtPrivate::QMetaTypeInterface *type() noexcept
-    {
-        using namespace QtPrivate;
-        using Query = TypeAndForceComplete<T, RequireComplete>;
-        return qTryMetaTypeInterfaceForType<Unique, Query>();
-    }
+// void as the Unique type (used by moc if --require-complete-types is passed
+// or some internal heuristic for QML matches) or by using the enum below, for
+// properties and enums.
+enum TypeCompletenessForMetaType : bool {
+    TypeMayBeIncomplete = false,
+    TypeMustBeComplete = true,
 };
 
-template <typename Unique, typename T, typename RequireComplete>
-struct TryMetaTypeInterfaceForType<Unique, ForceCompleteMetaTypes<T>, RequireComplete> :
-        TryMetaTypeInterfaceForType<void, T, std::true_type>
-{};
-
-template <typename... T> struct MetaTypeList
+template <bool TypeMustBeComplete, typename... T> struct MetaTypeList
 {
     static constexpr int count() { return sizeof...(T); }
     template <typename Unique, typename Result> static constexpr void
@@ -181,8 +165,9 @@ template <typename... T> struct MetaTypeList
     {
         if constexpr (count()) {
             using namespace QtPrivate;
+            using U = std::conditional_t<TypeMustBeComplete, void, Unique>;
             const QMetaTypeInterface *metaTypes[] = {
-                TryMetaTypeInterfaceForType<Unique, T>::type()...
+                qTryMetaTypeInterfaceForType<U, T>()...
             };
             for (const QMetaTypeInterface *mt : metaTypes)
                 result.relocatingData.metaTypes[metatypeoffset++] = mt;
@@ -315,7 +300,7 @@ template <typename PropertyType> struct PropertyData : detail::UintDataBlock<5,
     }
 
     static constexpr auto metaTypes()
-    { return detail::MetaTypeList<ForceCompleteMetaTypes<PropertyType>>{}; }
+    { return detail::MetaTypeList<detail::TypeMustBeComplete, PropertyType>{}; }
 
     static constexpr void adjustOffsets(uint *, uint, uint, uint) noexcept {}
 };
@@ -371,7 +356,7 @@ public:
     }
 
     static constexpr auto metaTypes()
-    { return detail::MetaTypeList<ForceCompleteMetaTypes<Enum>>{}; }
+    { return detail::MetaTypeList<detail::TypeMustBeComplete, Enum>{}; }
 
     static constexpr void
     adjustOffsets(uint *ptr, uint dataoffset, uint payloadoffset, uint metatypeoffset) noexcept
@@ -402,11 +387,11 @@ struct FunctionData<Ret (Args...), ExtraFlags>
                     "NoType return type used on a non-constructor");
             static_assert((ExtraFlags & MethodIsConst) == 0,
                     "Constructors cannot be const");
-            return detail::MetaTypeList<Args...>{};
+            return detail::MetaTypeList<detail::TypeMayBeIncomplete, Args...>{};
         } else {
             static_assert((ExtraFlags & MethodConstructor) != MethodConstructor,
                     "Constructors must use NoType as return type");
-            return detail::MetaTypeList<Ret, Args...>{};
+            return detail::MetaTypeList<detail::TypeMayBeIncomplete, Ret, Args...>{};
         }
     }
 
diff --git a/src/tools/moc/generator.cpp b/src/tools/moc/generator.cpp
index 43583b35528..cf4679b2156 100644
--- a/src/tools/moc/generator.cpp
+++ b/src/tools/moc/generator.cpp
@@ -329,9 +329,9 @@ void Generator::generateCode()
         metaObjectFlags = "QMC::PropertyAccessInStaticMetaCall";
     }
     {
-        QByteArray tagType = "qt_meta_tag_" + qualifiedClassNameIdentifier +  "_t";
-        if (requireCompleteness)
-            tagType = "QtMocHelpers::ForceCompleteMetaTypes<" + tagType + '>';
+        QByteArray tagType = QByteArrayLiteral("void");
+        if (!requireCompleteness)
+            tagType = "qt_meta_tag_" + qualifiedClassNameIdentifier +  "_t";
         fprintf(out, "    return QtMocHelpers::metaObjectData<%s, %s>(%s, qt_stringData,\n"
                      "            qt_methods, qt_properties, qt_enums%s);\n"
                      "}\n",
diff --git a/tests/auto/tools/mochelpers/tst_mochelpers.cpp b/tests/auto/tools/mochelpers/tst_mochelpers.cpp
index 022263e7d81..7e5d18d160e 100644
--- a/tests/auto/tools/mochelpers/tst_mochelpers.cpp
+++ b/tests/auto/tools/mochelpers/tst_mochelpers.cpp
@@ -699,7 +699,7 @@ void tst_MocHelpers::uintArray()
     using Dummy = QString;
     using QtMocHelpers::NoType;
     using namespace QtMocConstants;
-    constexpr auto mo = QtMocHelpers::metaObjectData<void, void>(PropertyAccessInStaticMetaCall,
+    constexpr auto mo = QtMocHelpers::metaObjectData<tst_MocHelpers, tst_MocHelpers>(PropertyAccessInStaticMetaCall,
             dummyStringData,
             QtMocHelpers::UintData{
                 QtMocHelpers::RevisionedSignalData<void()>(1, 2, QtMocConstants::AccessPublic, 0x509,
@@ -747,7 +747,7 @@ void tst_MocHelpers::uintArray()
     checkMethods(data, metaTypes);
     checkConstructors(data, metaTypes);
     QMetaType self(metaTypes[data[6] + data[8]]);
-    QCOMPARE(self, QMetaType::fromType<void>());
+    QCOMPARE(self, QMetaType::fromType<tst_MocHelpers>());
 }
 
 QTEST_MAIN(tst_MocHelpers)