feature_select: finish properties and postpone static properties

Static properties are not easy to support.
They need an extra property subtype and support in the meta-class.

A problem is that the implementation needs to go deeply into the
innards of things and need to use `_PyType_Lookup`.
That is hard to circumvent when the limited API is used.

Therefore, the current implementation will be it for 5.15 .
At most we might add a few missing properties through XML.

Task-number: PYSIDE-1019
Change-Id: I56a9eabe5f774c1ff04c149227e06318c8bf4f29
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

3 files changed, 80 insertions, 4 deletions

diff --git a/sources/pyside2/libpyside/feature_select.cpp b/sources/pyside2/libpyside/feature_select.cpp
index b26810add..6a21d168d 100644
--- a/sources/pyside2/libpyside/feature_select.cpp
+++ b/sources/pyside2/libpyside/feature_select.cpp
@@ -445,6 +445,8 @@ void finalize()
         Py_DECREF(fast_id_array[idx]);
 }
 
+static bool patch_property_impl();
+
 void init()
 {
     // This function can be called multiple times.
@@ -457,6 +459,7 @@ void init()
         featurePointer = featureProcArray;
         initSelectableFeature(SelectFeatureSet);
         registerCleanupFunction(finalize);
+        patch_property_impl();
         is_initialized = true;
     }
     // Reset the cache. This is called at any "from __feature__ import".
@@ -551,9 +554,8 @@ static PyObject *createProperty(PyObject *getter, PyObject *setter)
     assert(getter != nullptr);
     if (setter == nullptr)
         setter = Py_None;
-    PyObject *prop = PyObject_CallObject(reinterpret_cast<PyObject *>(&PyProperty_Type), nullptr);
-    AutoDecRef args(Py_BuildValue("OO", getter, setter));
-    PyProperty_Type.tp_init(prop, args, nullptr);
+    auto obtype = reinterpret_cast<PyObject *>(&PyProperty_Type);
+    PyObject *prop = PyObject_CallFunctionObjArgs(obtype, getter, setter, nullptr);
     return prop;
 }
 
@@ -635,6 +637,77 @@ static bool feature_02_true_property(PyTypeObject *type, PyObject *prev_dict, in
 
 //////////////////////////////////////////////////////////////////////////////
 //
+// These are a number of patches to make Python's property object better
+// suitable for us.
+// We turn `__doc__` into a lazy attribute saving signature initialization.
+//
+// Currently, there is no static extension planned, because _PyType_Lookup
+// and Limited_API are hard to use at the same time.
+//
+
+typedef struct {
+    PyObject_HEAD
+    PyObject *prop_get;
+    PyObject *prop_set;
+    PyObject *prop_del;
+    PyObject *prop_doc;
+    int getter_doc;
+} propertyobject;
+
+static PyObject *property_doc_get(PyObject *self, void *)
+{
+    auto po = reinterpret_cast<propertyobject *>(self);
+
+    if (po->prop_doc != nullptr && po->prop_doc != Py_None) {
+        Py_INCREF(po->prop_doc);
+        return po->prop_doc;
+    }
+    if (po->prop_get) {
+        // PYSIDE-1019: Fetch the default `__doc__` from fget. We do it late.
+        auto txt = PyObject_GetAttr(po->prop_get, PyMagicName::doc());
+        if (txt != nullptr) {
+            Py_INCREF(txt);
+            po->prop_doc = txt;
+            Py_INCREF(txt);
+            return txt;
+        }
+        PyErr_Clear();
+    }
+    Py_RETURN_NONE;
+}
+
+static int property_doc_set(PyObject *self, PyObject *value, void *)
+{
+    auto po = reinterpret_cast<propertyobject *>(self);
+
+    Py_INCREF(value);
+    po->prop_doc = value;
+    return 0;
+}
+
+static PyGetSetDef property_getset[] = {
+    // This gets added to the existing getsets
+    {const_cast<char *>("__doc__"), property_doc_get, property_doc_set, nullptr, nullptr},
+    {nullptr, nullptr, nullptr, nullptr, nullptr}
+};
+
+static bool patch_property_impl()
+{
+    // Turn `__doc__` into a computed attribute without changing writability.
+    auto gsp = property_getset;
+    auto type = &PyProperty_Type;
+    auto dict = type->tp_dict;
+    AutoDecRef descr(PyDescr_NewGetSet(type, gsp));
+    if (descr.isNull())
+        return false;
+    if (PyDict_SetItemString(dict, gsp->name, descr) < 0)
+        return false;
+    // Replace property_descr_get/set by slightly changed versions
+    return true;
+}
+
+//////////////////////////////////////////////////////////////////////////////
+//
 // PYSIDE-1019: Support switchable extensions
 //
 //     Feature 0x04..0x40: A fake switchable option for testing
diff --git a/sources/shiboken2/libshiboken/pep384impl.cpp b/sources/shiboken2/libshiboken/pep384impl.cpp
index 6e4926370..cb8042561 100644
--- a/sources/shiboken2/libshiboken/pep384impl.cpp
+++ b/sources/shiboken2/libshiboken/pep384impl.cpp
@@ -95,6 +95,7 @@ static PyMemberDef probe_members[] = {
 #define probe_tp_members    probe_members
 #define probe_tp_getset     probe_getseters
 #define probe_tp_descr_get  make_dummy(10)
+#define probe_tp_descr_set  make_dummy(18)
 #define probe_tp_init       make_dummy(11)
 #define probe_tp_alloc      make_dummy(12)
 #define probe_tp_new        make_dummy(13)
@@ -118,6 +119,7 @@ static PyType_Slot typeprobe_slots[] = {
     {Py_tp_members,     probe_tp_members},
     {Py_tp_getset,      probe_tp_getset},
     {Py_tp_descr_get,   probe_tp_descr_get},
+    {Py_tp_descr_set,   probe_tp_descr_set},
     {Py_tp_init,        probe_tp_init},
     {Py_tp_alloc,       probe_tp_alloc},
     {Py_tp_new,         probe_tp_new},
@@ -167,6 +169,7 @@ check_PyTypeObject_valid()
         || !PyDict_Check(check->tp_dict)
         || !PyDict_GetItemString(check->tp_dict, "dummy")
         || probe_tp_descr_get       != check->tp_descr_get
+        || probe_tp_descr_set       != check->tp_descr_set
         || probe_tp_dictoffset      != typetype->tp_dictoffset
         || probe_tp_init            != check->tp_init
         || probe_tp_alloc           != check->tp_alloc
diff --git a/sources/shiboken2/libshiboken/pep384impl.h b/sources/shiboken2/libshiboken/pep384impl.h
index 4b3e32ea2..7a6f57fcd 100644
--- a/sources/shiboken2/libshiboken/pep384impl.h
+++ b/sources/shiboken2/libshiboken/pep384impl.h
@@ -115,7 +115,7 @@ typedef struct _typeobject {
     struct _typeobject *tp_base;
     PyObject *tp_dict;
     descrgetfunc tp_descr_get;
-    void *X33; // descrsetfunc tp_descr_set;
+    descrsetfunc tp_descr_set;
     Py_ssize_t tp_dictoffset;
     initproc tp_init;
     allocfunc tp_alloc;