From ef0e13257ddd57c967000213e3c9812b3c08da91 Mon Sep 17 00:00:00 2001
From: Fabian Kosmale <fabian.kosmale@qt.io>
Date: Tue, 1 Mar 2022 11:25:11 +0100
Subject: [PATCH] QMetaObjectBuilder: Always set Data::metatypes

The array of metatypes should always contain at least one entry (for the
metatype of the current metaobject itself).
This prevents crashes in the case of a metaobject without meta-methods
and properties (as observed in Qt for Python).

Pick-to: 6.2 6.3
Change-Id: I7a6fb316eea48c4852b6f1c26e0a930aeba4c799
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
---
 src/corelib/kernel/qmetaobjectbuilder.cpp     | 56 +++++++++----------
 .../tst_qmetaobjectbuilder.cpp                | 12 ++++
 2 files changed, 39 insertions(+), 29 deletions(-)

diff --git a/src/corelib/kernel/qmetaobjectbuilder.cpp b/src/corelib/kernel/qmetaobjectbuilder.cpp
index 4f762b5e96..931dcfe2fd 100644
--- a/src/corelib/kernel/qmetaobjectbuilder.cpp
+++ b/src/corelib/kernel/qmetaobjectbuilder.cpp
@@ -1439,41 +1439,39 @@ static int buildMetaObject(QMetaObjectBuilderPrivate *d, char *buf,
         size += sizeof(SuperData) * (d->relatedMetaObjects.size() + 1);
     }
 
-    if (d->properties.size() > 0 || d->methods.size() > 0 || d->constructors.size() > 0) {
-        ALIGN(size, QtPrivate::QMetaTypeInterface *);
-        auto types = reinterpret_cast<QtPrivate::QMetaTypeInterface **>(buf + size);
-        if constexpr (mode == Construct) {
-            meta->d.metaTypes = types;
-            for (const auto &prop : d->properties) {
-                QMetaType mt = prop.metaType;
-                *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
-                types++;
-            }
-            // add metatype interface for this metaobject - must be null
-            // as we can't know our metatype
-            *types = nullptr;
+    ALIGN(size, QtPrivate::QMetaTypeInterface *);
+    auto types = reinterpret_cast<QtPrivate::QMetaTypeInterface **>(buf + size);
+    if constexpr (mode == Construct) {
+        meta->d.metaTypes = types;
+        for (const auto &prop : d->properties) {
+            QMetaType mt = prop.metaType;
+            *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
             types++;
-            for (const auto &method: d->methods) {
-                QMetaType mt(QMetaType::fromName(method.returnType).id());
+        }
+        // add metatype interface for this metaobject - must be null
+        // as we can't know our metatype
+        *types = nullptr;
+        types++;
+        for (const auto &method: d->methods) {
+            QMetaType mt(QMetaType::fromName(method.returnType).id());
+            *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
+            types++;
+            for (const auto &parameterType: method.parameterTypes()) {
+                QMetaType mt = QMetaType::fromName(parameterType);
+                *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
+                types++;
+            }
+        }
+        for (const auto &constructor : d->constructors) {
+            for (const auto &parameterType : constructor.parameterTypes()) {
+                QMetaType mt = QMetaType::fromName(parameterType);
                 *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
                 types++;
-                for (const auto &parameterType: method.parameterTypes()) {
-                    QMetaType mt = QMetaType::fromName(parameterType);
-                    *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
-                    types++;
-                }
-            }
-            for (const auto &constructor : d->constructors) {
-                for (const auto &parameterType : constructor.parameterTypes()) {
-                    QMetaType mt = QMetaType::fromName(parameterType);
-                    *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
-                    types++;
-                }
             }
         }
-        // parameterMetaTypesIndex is equal to the total number of metatypes
-        size += sizeof(QMetaType) * parameterMetaTypesIndex;
     }
+    // parameterMetaTypesIndex is equal to the total number of metatypes
+    size += sizeof(QMetaType) * parameterMetaTypesIndex;
 
     // Align the final size and return it.
     ALIGN(size, void *);
diff --git a/tests/auto/corelib/kernel/qmetaobjectbuilder/tst_qmetaobjectbuilder.cpp b/tests/auto/corelib/kernel/qmetaobjectbuilder/tst_qmetaobjectbuilder.cpp
index 188a5a6626..9e96d0e02c 100644
--- a/tests/auto/corelib/kernel/qmetaobjectbuilder/tst_qmetaobjectbuilder.cpp
+++ b/tests/auto/corelib/kernel/qmetaobjectbuilder/tst_qmetaobjectbuilder.cpp
@@ -67,6 +67,8 @@ private slots:
 
     void cleanupTestCase();
 
+    void ownMetaTypeNoProperties();
+
 private:
     static bool checkForSideEffects
         (const QMetaObjectBuilder& builder,
@@ -1657,6 +1659,16 @@ void tst_QMetaObjectBuilder::propertyMetaType()
     free(mo);
 }
 
+void tst_QMetaObjectBuilder::ownMetaTypeNoProperties()
+{
+    QMetaObjectBuilder builder;
+    builder.setClassName("NoProperties");
+    auto mo = builder.toMetaObject();
+    auto cleanup = qScopeGuard([&](){ free(mo); });
+    // own metatype should be invalid, as the dynamic metaobject has not been registered
+    QVERIFY(!mo->metaType().isValid());// should not crash
+}
+
 void tst_QMetaObjectBuilder::cleanupTestCase()
 {
     for (QMetaObject *obj: dynamicMetaObjectsPendingFree)