__feature__: heavily rework the context switching

The example of the issue shows the qasync.py module which
fails miserably when using snake_case.

The reason:
-----------
Reason is the way how feature switching is implemented.
Modules like qasync get a default switching of "ignore".
This ignores that the qasync module itself imports QtCore,
and feature switching is of course relevant, suggesting
a default setting of "normal" (explicitly no features).

The real problem:
-----------------

Testing the simple approach showed a serious problem with
feature switching: The functions get switched when a certain
function (getattr etc.) is called.
But the switching is sometimes not done due to a caching problem.

This fix removes caching that was wrong. Optimization will
be done in a different step with a different approach.
This Change was not qasync specific, but happens with PySide imports.

Actions done:
- adjust the inline structure
- implement a feature_imported callback
- identify Python functions that use PySide during import

[ChangeLog][PySide6] __feature__ switching now works even with
                     recursive imports like in the qasync module.

Fixes: PYSIDE-2029
Change-Id: I3340f54f293083a09fb509383688f73bbd9b60ae
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
(cherry picked from commit 7377d2b8130ce7290775cd8a343e75c0561fc854)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

9 files changed, 132 insertions, 40 deletions

diff --git a/sources/pyside6/libpyside/feature_select.cpp b/sources/pyside6/libpyside/feature_select.cpp
index b3117d40d..17c6169af 100644
--- a/sources/pyside6/libpyside/feature_select.cpp
+++ b/sources/pyside6/libpyside/feature_select.cpp
@@ -163,15 +163,6 @@ static inline void setCurrentSelectId(PyTypeObject *type, int id)
     SbkObjectType_SetReserved(type, id);
 }
 
-static inline PyObject *getCurrentSelectId(PyTypeObject *type)
-{
-    int id = SbkObjectType_GetReserved(type);
-    // This can be too early.
-    if (id < 0)
-        id = 0;
-    return fast_id_array[id];
-}
-
 static bool replaceClassDict(PyTypeObject *type)
 {
     /*
@@ -218,7 +209,7 @@ static bool addNewDict(PyTypeObject *type, PyObject *select_id)
     return true;
 }
 
-static bool moveToFeatureSet(PyTypeObject *type, PyObject *select_id)
+static inline bool moveToFeatureSet(PyTypeObject *type, PyObject *select_id)
 {
     /*
      * Rotate the ring to the given `select_id` and return `true`.
@@ -227,7 +218,6 @@ static bool moveToFeatureSet(PyTypeObject *type, PyObject *select_id)
     auto initial_dict = type->tp_dict;
     auto dict = initial_dict;
     do {
-        dict = nextInCircle(dict);
         AutoDecRef current_id(getSelectId(dict));
         // This works because small numbers are singleton objects.
         if (current_id == select_id) {
@@ -235,6 +225,7 @@ static bool moveToFeatureSet(PyTypeObject *type, PyObject *select_id)
             setCurrentSelectId(type, select_id);
             return true;
         }
+        dict = nextInCircle(dict);
     } while (dict != initial_dict);
     type->tp_dict = initial_dict;
     setCurrentSelectId(type, getSelectId(initial_dict));
@@ -290,7 +281,7 @@ static bool createNewFeatureSet(PyTypeObject *type, PyObject *select_id)
     return true;
 }
 
-static bool SelectFeatureSetSubtype(PyTypeObject *type, PyObject *select_id)
+static inline bool SelectFeatureSetSubtype(PyTypeObject *type, PyObject *select_id)
 {
     /*
      * This is the selector for one sublass. We need to call this for
@@ -330,28 +321,21 @@ static inline void SelectFeatureSet(PyTypeObject *type)
             return;
         }
     }
+
     PyObject *select_id = getFeatureSelectId();         // borrowed
-    PyObject *current_id = getCurrentSelectId(type);    // borrowed
-    static PyObject *undef = fast_id_array[-1];
-
-    // PYSIDE-1019: During import PepType_SOTP is still zero.
-    if (current_id == undef)
-        current_id = select_id = fast_id_array[0];
-
-    if (select_id != current_id) {
-        PyObject *mro = type->tp_mro;
-        Py_ssize_t idx, n = PyTuple_GET_SIZE(mro);
-        // We leave 'Shiboken.Object' and 'object' alone, therefore "n - 2".
-        for (idx = 0; idx < n - 2; idx++) {
-            auto *sub_type = reinterpret_cast<PyTypeObject *>(PyTuple_GET_ITEM(mro, idx));
-            // When any subtype is already resolved (false), we can stop.
-            if (!SelectFeatureSetSubtype(sub_type, select_id))
-                break;
-        }
-        // PYSIDE-1436: Clear all caches for the type and subtypes.
-        PyType_Modified(type);
+
+    // PYSIDE-2029: We are no longer caching extremely, but switching safe.
+    PyObject *mro = type->tp_mro;
+    Py_ssize_t idx, n = PyTuple_GET_SIZE(mro);
+    // We leave 'Shiboken.Object' and 'object' alone, therefore "n - 2".
+    for (idx = 0; idx < n - 2; idx++) {
+        auto *sub_type = reinterpret_cast<PyTypeObject *>(PyTuple_GET_ITEM(mro, idx));
+        // When any subtype is already resolved (false), we can stop.
+        if (!SelectFeatureSetSubtype(sub_type, select_id))
+            break;
     }
-    return;
+    // PYSIDE-1436: Clear all caches for the type and subtypes.
+    PyType_Modified(type);
 }
 
 // For cppgenerator:
diff --git a/sources/pyside6/tests/pysidetest/CMakeLists.txt b/sources/pyside6/tests/pysidetest/CMakeLists.txt
index 3965455c9..eaf748517 100644
--- a/sources/pyside6/tests/pysidetest/CMakeLists.txt
+++ b/sources/pyside6/tests/pysidetest/CMakeLists.txt
@@ -144,6 +144,7 @@ PYSIDE_TEST(new_inherited_functions_test.py)
 PYSIDE_TEST(notify_id.py)
 PYSIDE_TEST(properties_test.py)
 PYSIDE_TEST(property_python_test.py)
+PYSIDE_TEST(snake_case_test.py)
 PYSIDE_TEST(true_property_test.py)
 PYSIDE_TEST(qapp_like_a_macro_test.py)
 PYSIDE_TEST(qvariant_test.py)
diff --git a/sources/pyside6/tests/pysidetest/snake_case_sub.py b/sources/pyside6/tests/pysidetest/snake_case_sub.py
new file mode 100644
index 000000000..5056d50bb
--- /dev/null
+++ b/sources/pyside6/tests/pysidetest/snake_case_sub.py
@@ -0,0 +1,22 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+import os
+import sys
+import unittest
+
+from pathlib import Path
+sys.path.append(os.fspath(Path(__file__).resolve().parents[1]))
+from init_paths import init_test_paths
+init_test_paths(False)
+
+"""
+PYSIDE-2029: Tests that snake_case is isolated from imported modules
+"""
+
+from PySide6.QtWidgets import QWidget
+
+def test_no_snake_case():
+    print(__name__)
+    widget = QWidget()
+    check = widget.sizeHint
diff --git a/sources/pyside6/tests/pysidetest/snake_case_test.py b/sources/pyside6/tests/pysidetest/snake_case_test.py
new file mode 100644
index 000000000..aaa3d3f2a
--- /dev/null
+++ b/sources/pyside6/tests/pysidetest/snake_case_test.py
@@ -0,0 +1,34 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+import os
+import sys
+import unittest
+
+from pathlib import Path
+sys.path.append(os.fspath(Path(__file__).resolve().parents[1]))
+from init_paths import init_test_paths
+init_test_paths(False)
+
+"""
+PYSIDE-2029: Tests that snake_case is isolated from imported modules
+"""
+
+from PySide6.QtCore import QSize
+from PySide6.QtWidgets import QWidget, QSpinBox
+from __feature__ import snake_case
+from helper.usesqapplication import UsesQApplication
+
+import snake_case_sub
+
+class SnakeCaseNoPropagateTest(UsesQApplication):
+
+    def testSnakeCase(self):
+        # this worked
+        widget = QWidget()
+        check = widget.size_hint
+
+        snake_case_sub.test_no_snake_case()
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/sources/shiboken6/libshiboken/signature/signature.cpp b/sources/shiboken6/libshiboken/signature/signature.cpp
index 6c28c758b..808edc5cf 100644
--- a/sources/shiboken6/libshiboken/signature/signature.cpp
+++ b/sources/shiboken6/libshiboken/signature/signature.cpp
@@ -284,7 +284,18 @@ static PyObject *feature_import(PyObject * /* self */, PyObject *args, PyObject
     if (import_func == nullptr) {
         Py_FatalError("builtins has no \"__orig_import__\" function");
     }
-    return PyObject_Call(import_func, args, kwds);
+    ret = PyObject_Call(import_func, args, kwds);
+    if (ret) {
+        // PYSIDE-2029: Intercept after the import to search for PySide usage.
+        PyObject *post = PyObject_CallFunctionObjArgs(pyside_globals->feature_imported_func,
+                                                      ret, nullptr);
+        Py_XDECREF(post);
+        if (post == nullptr) {
+            Py_DECREF(ret);
+            return nullptr;
+        }
+    }
+    return ret;
 }
 
 PyMethodDef signature_methods[] = {
diff --git a/sources/shiboken6/libshiboken/signature/signature_globals.cpp b/sources/shiboken6/libshiboken/signature/signature_globals.cpp
index b861e791a..d0ea86fc6 100644
--- a/sources/shiboken6/libshiboken/signature/signature_globals.cpp
+++ b/sources/shiboken6/libshiboken/signature/signature_globals.cpp
@@ -186,6 +186,9 @@ static int init_phase_2(safe_globals_struc *p, PyMethodDef *methods)
         p->feature_import_func = PyObject_GetAttrString(loader, "feature_import");
         if (p->feature_import_func == nullptr)
             break;
+        p->feature_imported_func = PyObject_GetAttrString(loader, "feature_imported");
+        if (p->feature_imported_func == nullptr)
+            break;
         return 0;
 
     } while (0);
diff --git a/sources/shiboken6/libshiboken/signature_p.h b/sources/shiboken6/libshiboken/signature_p.h
index faa98f93c..7ea03877a 100644
--- a/sources/shiboken6/libshiboken/signature_p.h
+++ b/sources/shiboken6/libshiboken/signature_p.h
@@ -24,6 +24,7 @@ typedef struct safe_globals_struc {
     PyObject *make_helptext_func;
     PyObject *finish_import_func;
     PyObject *feature_import_func;
+    PyObject *feature_imported_func;
 } safe_globals_struc, *safe_globals;
 
 extern safe_globals pyside_globals;
diff --git a/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/feature.py b/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/feature.py
index 92bc30d2b..5171d59e9 100644
--- a/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/feature.py
+++ b/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/feature.py
@@ -18,6 +18,7 @@ and takes an optional `mod_name` parameter.
 The select id `-1` has the spectial meaning "ignore this module".
 """
 
+import inspect
 import sys
 from contextlib import contextmanager
 
@@ -84,6 +85,7 @@ def feature_import(name, *args, **kwargs):
     # PYSIDE-1398: sys._getframe(1) may not exist when embedding.
     # PYSIDE-1338: The "1" below is the redirection in loader.py .
     # PYSIDE-1548: Ensure that features are not affected by other imports.
+    # PYSIDE-2029: Need to always switch. The cache was wrong interpreted.
     calling_frame = _cf = sys._getframe(1).f_back
     importing_module = _cf.f_globals.get("__name__", "__main__") if _cf else "__main__"
     existing = pyside_feature_dict.get(importing_module, 0)
@@ -105,11 +107,6 @@ def feature_import(name, *args, **kwargs):
         # Initialize feature (multiple times allowed) and clear cache.
         sys.modules["PySide6.QtCore"].__init_feature__()
         return sys.modules["__feature__"]
-
-    if importing_module not in pyside_feature_dict:
-        # Ignore new modules if not from PySide.
-        default = 0 if name.split(".")[0] == "PySide6" else -1
-        pyside_feature_dict[importing_module] = default
     # Redirect to the original import
     return None
 
@@ -121,11 +118,43 @@ def __init__():
         # use _one_ recursive import...
         import PySide6.QtCore
         # Initialize all prior imported modules
-        for name in sys.modules:
-            pyside_feature_dict.setdefault(name, -1)
+        for name, module in sys.modules.items():
+            if name not in pyside_feature_dict:
+                pyside_feature_dict[name] = 0 if _mod_uses_pyside(module) else -1
         _is_initialized = True
 
 
+def feature_imported(module):
+    # PYSIDE-2029: Need to inspect imported modules for PySide usage.
+    """
+    Set the module feature default after import.
+
+    A module that uses PySide has a switching default of 0 = "no feature".
+    Otherwise the default is -1 = "ignore this module".
+    """
+    name = module.__name__
+    if name not in pyside_feature_dict:
+        pyside_feature_dict[name] = 0 if _mod_uses_pyside(module) else -1
+
+
+def _mod_uses_pyside(module):
+    """
+    Find out if this module uses PySide.
+
+    Simple approach: Search the source code for the string "PySide6".
+    Maybe we later support source-less modules by inspecting all code objects.
+    """
+    try:
+        source = inspect.getsource(module)
+    except TypeError:
+        # this is a builtin module like sys
+        return False
+    except OSError:
+        # this is a module withot source file
+        return False
+    return "PySide6" in source
+
+
 def set_selection(select_id, mod_name=None):
     """
     Internal use: Set the feature directly by Id.
diff --git a/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/loader.py b/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/loader.py
index 34977f3bd..b6a432ba9 100644
--- a/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/loader.py
+++ b/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/loader.py
@@ -53,6 +53,13 @@ def feature_import(*args, **kwds):
     feature_import = feature.feature_import
     return feature_import(*args, **kwds)
 
+# name used in signature.cpp
+def feature_imported(*args, **kwds):
+    # don't spend a stack level here for speed and compatibility
+    global feature_imported
+    feature_imported = feature.feature_imported
+    return feature_imported(*args, **kwds)
+
 
 import builtins
 import signature_bootstrap