Fix build for non-limited API

e55c87131a66e1cd11b13663b66582412cd38788 broke the build
for the non-limited API due to removing a C-style cast from
a code snippet:

%0 = PyBytes_GET_SIZE((PyObject *)%PYARG_0);

in the overridden method of a C++ wrapper class.
PyBytes_GET_SIZE(op) is defined to use PyVarObject*)(op)),
which does not work when passing an AutoDecRef instance
which is used for pyResult in that case.

To fix this, make the placeholder a smarter; append
.object() unless the code snippet invokes a member
function itself.

[ChangeLog][shiboken6] The replacement of %PYARG_0 in
C++ wrapper classes (native) has been improved and no
longer requires adding casts to PyObject *.

Change-Id: Ia31b28d568603f96c93e564e5ef7554cb2468b04
Reviewed-by: Christian Tismer <tismer@stackless.com>

2 files changed, 29 insertions, 2 deletions

diff --git a/sources/shiboken6/generator/shiboken/shibokengenerator.cpp b/sources/shiboken6/generator/shiboken/shibokengenerator.cpp
index 8a24e8327..60d7a5a2c 100644
--- a/sources/shiboken6/generator/shiboken/shibokengenerator.cpp
+++ b/sources/shiboken6/generator/shiboken/shibokengenerator.cpp
@@ -1615,6 +1615,33 @@ void ShibokenGenerator::writeCodeSnips(TextStream &s,
     s << "// Begin code injection\n" << code << "// End of code injection\n\n";
 }
 
+static void replacePyArg0(TypeSystem::Language language, QString *code)
+{
+    static const QString pyArg0 = u"%PYARG_0"_qs;
+    static const QString pyReturn = QLatin1String(PYTHON_RETURN_VAR);
+
+    if (!code->contains(pyArg0))
+        return;
+    if (language != TypeSystem::NativeCode) {
+        code->replace(pyArg0, pyReturn);
+        return;
+    }
+
+    // pyResult is an AutoDecRef in overridden methods of wrapper classes which
+    // has a cast operator for PyObject *. This may however not work in all
+    // situations (fex _PyVarObject_CAST(op) defined as ((PyVarObject*)(op))).
+    // Append ".object()" unless it is followed by a '.' indicating explicit
+    // AutoDecRef member invocation.
+    static const QString pyObject = pyReturn + u".object()"_qs;
+    qsizetype pos{};
+    while ( (pos = code->indexOf(pyArg0)) >= 0) {
+        const auto next = pos + pyArg0.size();
+        const bool memberInvocation = next < code->size() && code->at(next) == u'.';
+        code->replace(pos, pyArg0.size(),
+                      memberInvocation ? pyReturn : pyObject);
+    }
+}
+
 void ShibokenGenerator::writeCodeSnips(TextStream &s,
                                        const CodeSnipList &codeSnips,
                                        TypeSystem::CodeSnipPosition position,
@@ -1635,7 +1662,7 @@ void ShibokenGenerator::writeCodeSnips(TextStream &s,
     }
 
     // Replace %PYARG_# variables.
-    code.replace(QLatin1String("%PYARG_0"), QLatin1String(PYTHON_RETURN_VAR));
+    replacePyArg0(language, &code);
 
     static const QRegularExpression pyArgsRegex(QStringLiteral("%PYARG_(\\d+)"));
     Q_ASSERT(pyArgsRegex.isValid());
diff --git a/sources/shiboken6/tests/samplebinding/typesystem_sample.xml b/sources/shiboken6/tests/samplebinding/typesystem_sample.xml
index bc5052e49..95c51938e 100644
--- a/sources/shiboken6/tests/samplebinding/typesystem_sample.xml
+++ b/sources/shiboken6/tests/samplebinding/typesystem_sample.xml
@@ -1445,7 +1445,7 @@
         PyTuple_SET_ITEM(%PYARG_0, 3, %CONVERTTOPYTHON[int](a3));
         </template>
         <template name="fix_native_return_int*,int*,int*,int*">
-            PyObject* _obj = %PYARG_0.object();
+            PyObject* _obj = %PYARG_0;
             if (!PySequence_Check(_obj)
                 || PySequence_Fast_GET_SIZE(_obj) != 4
                 || !PyNumber_Check(PySequence_Fast_GET_ITEM(_obj, 0))