shiboken6: Add a placeholder for the base class to polymorphic-id-expression

Add %B for base class in addition to %1 for the class itself, which
is not useful and may lead to undefined behavior.

As a drive-by fix up the hitherto unused "polymorphic-base" which
is a boolean indicating the base class.

Task-number: PYSIDE-2675
Change-Id: I078191dc7b4c686b196fe58d6df9a249cdf2b151
Reviewed-by: Christian Tismer <tismer@stackless.com>
(cherry picked from commit 4a04afc95d348c8f26919a2f084ee80fa404e7d9)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

4 files changed, 46 insertions, 5 deletions

diff --git a/sources/shiboken6/ApiExtractor/typesystemparser.cpp b/sources/shiboken6/ApiExtractor/typesystemparser.cpp
index 1c1565ac2..71e80cfa8 100644
--- a/sources/shiboken6/ApiExtractor/typesystemparser.cpp
+++ b/sources/shiboken6/ApiExtractor/typesystemparser.cpp
@@ -88,6 +88,7 @@ constexpr auto pyiTypeAttribute = "pyi-type"_L1;
 constexpr auto overloadNumberAttribute = "overload-number"_L1;
 constexpr auto ownershipAttribute = "owner"_L1;
 constexpr auto packageAttribute = "package"_L1;
+constexpr auto polymorphicBaseAttribute = "polymorphic-base"_L1;
 constexpr auto positionAttribute = "position"_L1;
 constexpr auto preferredConversionAttribute = "preferred-conversion"_L1;
 constexpr auto preferredTargetLangTypeAttribute = "preferred-target-lang-type"_L1;
@@ -1810,8 +1811,10 @@ void TypeSystemParser::applyComplexTypeAttributes(const ConditionalStreamReader
             ctype->setGenericClass(v);
         } else if (name == targetLangNameAttribute) {
             ctype->setTargetLangName(attributes->takeAt(i).value().toString());
-        } else if (name == u"polymorphic-base") {
-            ctype->setPolymorphicIdValue(attributes->takeAt(i).value().toString());
+        } else if (name == polymorphicBaseAttribute) {
+            const bool v = convertBoolean(attributes->takeAt(i).value(),
+                                          polymorphicBaseAttribute, false);
+            ctype->setIsPolymorphicBase(v);
         } else if (name == u"polymorphic-name-function") {
             ctype->setPolymorphicNameFunction(attributes->takeAt(i).value().toString());
         } else if (name == u"polymorphic-id-expression") {
diff --git a/sources/shiboken6/doc/typesystem_specifying_types.rst b/sources/shiboken6/doc/typesystem_specifying_types.rst
index 7a1471b44..66e68ae2b 100644
--- a/sources/shiboken6/doc/typesystem_specifying_types.rst
+++ b/sources/shiboken6/doc/typesystem_specifying_types.rst
@@ -453,6 +453,7 @@ or other type nodes and may contain :ref:`add-function`, :ref:`add-pymethoddef`,
          parent-management="yes | no"
          polymorphic-id-expression="..."
          polymorphic-name-function="..."
+         polymorphic-base="yes | no"
          private="yes | no"
          qt-metaobject="yes | no"
          qt-register-metatype = "yes | no | base"
@@ -540,6 +541,21 @@ expression checking whether a base class pointer is of the matching
 type. For example, in a ``virtual eventHandler(BaseEvent *e)``
 function, this is used to construct a Python wrapper matching
 the derived class (for example, a ``MouseEvent`` or similar).
+The attribute value may contain placeholders:
+
+%1
+    Fully qualified class name
+
+%B
+    Fully qualified name of the base class (found by base class
+    search or as indicated by **polymorphic-base**).
+
+To check for a class inheriting ``BaseEvent``, specify:
+
+.. code-block:: xml
+
+        <object-type name="MouseEvent"
+                     polymorphic-id-expression="%B-&gt;type() == BaseEvent::MouseEvent"/>
 
 The *optional* **polymorphic-name-function** specifies the name of a
 function returning the type name of a derived class on the base class
@@ -548,6 +564,10 @@ However, this fails if the type hierarchy does not have virtual functions.
 In this case, a function is required which typically decides depending
 on some type enumeration.
 
+The *optional* **polymorphic-base** attribute indicates
+whether the class is the base class of a class hierarchy
+(used for the *%B* placeholder in **polymorphic-id-expression**).
+
 interface-type
 ^^^^^^^^^^^^^^
 
diff --git a/sources/shiboken6/generator/shiboken/cppgenerator.cpp b/sources/shiboken6/generator/shiboken/cppgenerator.cpp
index 05539eb55..329b48d1c 100644
--- a/sources/shiboken6/generator/shiboken/cppgenerator.cpp
+++ b/sources/shiboken6/generator/shiboken/cppgenerator.cpp
@@ -5718,6 +5718,24 @@ void CppGenerator::writeInitQtMetaTypeFunctionBody(TextStream &s, const Generato
     }
 }
 
+void CppGenerator::replacePolymorphicIdPlaceHolders(const AbstractMetaClassCPtr &metaClass,
+                                                    QString *id)
+{
+    if (id->contains("%1"_L1)) {
+        QString replacement = " reinterpret_cast< "_L1 + m_gsp + metaClass->qualifiedCppName()
+                              + " *>(cptr)"_L1;
+        id->replace("%1"_L1, replacement);
+    }
+    if (id->contains("%B"_L1)) {
+        auto baseClass = metaClass;
+        while (!baseClass->typeEntry()->isPolymorphicBase() && baseClass->baseClass())
+            baseClass = baseClass->baseClass();
+        QString replacement = " reinterpret_cast< "_L1 + m_gsp + baseClass->qualifiedCppName()
+                              + " *>(cptr)"_L1;
+        id->replace("%B"_L1, replacement);
+    }
+}
+
 void CppGenerator::writeTypeDiscoveryFunction(TextStream &s,
                                               const AbstractMetaClassCPtr &metaClass)
 {
@@ -5729,9 +5747,7 @@ void CppGenerator::writeTypeDiscoveryFunction(TextStream &s,
         << sbkUnusedVariableCast("instanceType");
 
     if (!polymorphicExpr.isEmpty()) {
-        polymorphicExpr.replace(u"%1"_s, " reinterpret_cast< "_L1
-                                + m_gsp + metaClass->qualifiedCppName()
-                                         + " *>(cptr)"_L1);
+        replacePolymorphicIdPlaceHolders(metaClass, &polymorphicExpr);
         s << " if (" << polymorphicExpr << ")\n" << indent
             << "return cptr;\n" << outdent;
     } else if (metaClass->isPolymorphic()) {
diff --git a/sources/shiboken6/generator/shiboken/cppgenerator.h b/sources/shiboken6/generator/shiboken/cppgenerator.h
index 94ad87bbe..7e87fd9f3 100644
--- a/sources/shiboken6/generator/shiboken/cppgenerator.h
+++ b/sources/shiboken6/generator/shiboken/cppgenerator.h
@@ -192,6 +192,8 @@ private:
     static void writeTypeCheck(TextStream& s, const std::shared_ptr<OverloadDataNode> &overloadData,
                         const QString &argumentName);
 
+    static void replacePolymorphicIdPlaceHolders(const AbstractMetaClassCPtr &metaClass,
+                                                 QString *id);
     static void writeTypeDiscoveryFunction(TextStream &s,
                                            const AbstractMetaClassCPtr &metaClass);