shiboken6: Add a check for null to the smart pointer access

If a null check method exists, generate a check into getattro() with
a better error message than the attribute access error.
This will be vital for std::optional to suppress a C++ exception
being thrown.

Pick-to: 6.2
Task-number: PYSIDE-454
Change-Id: I6d8e16e31c094aa695e150990c471007bcd34eb9
Reviewed-by: Christian Tismer <tismer@stackless.com>

2 files changed, 21 insertions, 4 deletions

diff --git a/sources/shiboken6/generator/shiboken/cppgenerator.cpp b/sources/shiboken6/generator/shiboken/cppgenerator.cpp
index 1734237ba..64c748ca5 100644
--- a/sources/shiboken6/generator/shiboken/cppgenerator.cpp
+++ b/sources/shiboken6/generator/shiboken/cppgenerator.cpp
@@ -872,7 +872,7 @@ void CppGenerator::generateSmartPointerClass(TextStream &s, const GeneratorConte
 
     // Write tp_s/getattro function
     const auto boolCastOpt = boolCast(metaClass);
-    writeSmartPointerGetattroFunction(s, classContext);
+    writeSmartPointerGetattroFunction(s, classContext, boolCastOpt);
     writeSmartPointerSetattroFunction(s, classContext);
 
     if (boolCastOpt.has_value())
@@ -6305,7 +6305,9 @@ void CppGenerator::writeGetattroFunction(TextStream &s, AttroCheck attroCheck,
     s << "return " << getattrFunc << ";\n" << outdent << "}\n\n";
 }
 
-void CppGenerator::writeSmartPointerGetattroFunction(TextStream &s, const GeneratorContext &context)
+void CppGenerator::writeSmartPointerGetattroFunction(TextStream &s,
+                                                     const GeneratorContext &context,
+                                                     const BoolCastFunctionOptional &boolCast)
 {
     Q_ASSERT(context.forSmartPointer());
     const AbstractMetaClass *metaClass = context.metaClass();
@@ -6316,6 +6318,18 @@ void CppGenerator::writeSmartPointerGetattroFunction(TextStream &s, const Genera
         << indent << "return nullptr;\n" << outdent
         << "PyErr_Clear();\n";
 
+    if (boolCast.has_value()) {
+        writeSmartPointerCppSelfDefinition(s, context);
+        s << "if (";
+        writeNbBoolExpression(s, boolCast.value(), true /* invert */);
+        s << ") {\n" << indent
+          << R"(PyTypeObject *tp = Py_TYPE(self);
+PyErr_Format(PyExc_AttributeError, "Attempt to retrieve '%s' from null object '%s'.",
+             Shiboken::String::toCString(name), tp->tp_name);
+return nullptr;
+)" << outdent << "}\n";
+    }
+
     // This generates the code which dispatches access to member functions
     // and fields from the smart pointer to its pointee.
     s << smartPtrComment
diff --git a/sources/shiboken6/generator/shiboken/cppgenerator.h b/sources/shiboken6/generator/shiboken/cppgenerator.h
index 9f0dc6732..9bed05432 100644
--- a/sources/shiboken6/generator/shiboken/cppgenerator.h
+++ b/sources/shiboken6/generator/shiboken/cppgenerator.h
@@ -189,11 +189,14 @@ private:
 
     void writeSetattroDefinition(TextStream &s, const AbstractMetaClass *metaClass) const;
     static void writeSetattroDefaultReturn(TextStream &s);
-    void writeSmartPointerSetattroFunction(TextStream &s, const GeneratorContext &context) const;
+    void writeSmartPointerSetattroFunction(TextStream &s,
+                                           const GeneratorContext &context) const;
     void writeSetattroFunction(TextStream &s, AttroCheck attroCheck,
                                const GeneratorContext &context) const;
     static void writeGetattroDefinition(TextStream &s, const AbstractMetaClass *metaClass);
-    static void writeSmartPointerGetattroFunction(TextStream &s, const GeneratorContext &context);
+    static void writeSmartPointerGetattroFunction(TextStream &s,
+                                                  const GeneratorContext &context,
+                                                  const BoolCastFunctionOptional &boolCast);
     void writeGetattroFunction(TextStream &s, AttroCheck attroCheck,
                                const GeneratorContext &context) const;
     QString qObjectGetAttroFunction() const;