Fix 3 strange cases in QSettings.value() round trips of a list

- The "default value" parameter had an int 0 default value, which lead
  to strange behavior ['0'] being returned for string lists with
  missing keys.
- QStringList was not converted when forcing the type to be list
  due to the QByteArray split mechanism.
- String values could not be coerced to a list

Fix the default value to have a default {}.
Add a helper function checking whether a custom type conversion
is actually needed or the default QVariant converter can handle it.

Task-number: PYSIDE-2381
Change-Id: I91b22c05f851c2dc8c3792bd9f1446cfc8ceba51
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
(cherry picked from commit 3dfc872e356dd944d9cd03bccd8df5da8b1de472)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 56 insertions, 1 deletions

diff --git a/sources/pyside6/PySide6/glue/qtcore.cpp b/sources/pyside6/PySide6/glue/qtcore.cpp
index b90a98a51..a706042b4 100644
--- a/sources/pyside6/PySide6/glue/qtcore.cpp
+++ b/sources/pyside6/PySide6/glue/qtcore.cpp
@@ -99,6 +99,13 @@ static PyObject *convertToPrimitiveType(const QVariant &out, int metaTypeId)
 static PyObject *settingsTypeCoercion(const QVariant &out, PyTypeObject *typeObj)
 {
     if (typeObj == &PyList_Type) {
+        // Convert any string, etc, to a list of 1 element
+        if (auto *primitiveValue = convertToPrimitiveType(out, out.typeId())) {
+            PyObject *list = PyList_New(1);
+            PyList_SET_ITEM(list, 0, primitiveValue);
+            return list;
+        }
+
         const QByteArray out_ba = out.toByteArray();
         if (out_ba.isEmpty())
             return PyList_New(0);
@@ -132,6 +139,36 @@ static PyObject *settingsTypeCoercion(const QVariant &out, PyTypeObject *typeObj
     return nullptr;
 }
 
+static bool isEquivalentSettingsType(PyTypeObject *typeObj, int metaTypeId)
+{
+    switch (metaTypeId) {
+    case QMetaType::QVariantList:
+    case QMetaType::QStringList:
+        return typeObj == &PyList_Type;
+    case QMetaType::QByteArray:
+        return typeObj == &PyBytes_Type;
+    case QMetaType::QString:
+        return typeObj == &PyUnicode_Type;
+    case QMetaType::Short:
+    case QMetaType::Long:
+    case QMetaType::LongLong:
+    case QMetaType::UShort:
+    case QMetaType::ULong:
+    case QMetaType::ULongLong:
+    case QMetaType::Int:
+    case QMetaType::UInt:
+        return typeObj == &PyLong_Type;
+    case QMetaType::Double:
+    case QMetaType::Float:
+    case QMetaType::Float16:
+        return typeObj == &PyFloat_Type;
+    case QMetaType::Bool:
+        return typeObj == &PyBool_Type;
+    default:
+        break;
+    }
+    return false;
+}
 // @snippet settings-value-helpers
 
 // @snippet qsettings-value
@@ -154,7 +191,8 @@ if ((kwds && PyDict_Size(kwds) > 0) || numArgs > 1) {
 
 PyTypeObject *typeObj = reinterpret_cast<PyTypeObject*>(%PYARG_3);
 
-if (typeObj && !Shiboken::ObjectType::checkType(typeObj)) {
+if (typeObj && !Shiboken::ObjectType::checkType(typeObj)
+    && !isEquivalentSettingsType(typeObj, out.typeId())) {
     %PYARG_0 = settingsTypeCoercion(out, typeObj);
 } else {
     if (out.isValid()) {
diff --git a/sources/pyside6/tests/QtCore/qsettings_test.py b/sources/pyside6/tests/QtCore/qsettings_test.py
index 5bae79355..64ceffd70 100644
--- a/sources/pyside6/tests/QtCore/qsettings_test.py
+++ b/sources/pyside6/tests/QtCore/qsettings_test.py
@@ -51,8 +51,12 @@ class TestQSettings(unittest.TestCase):
         self.assertTrue(dir.isValid())
         file_name = dir.filePath('foo.ini')
         settings = QSettings(file_name, QSettings.IniFormat)
+        sample_list = ["a", "b"]
+        string_list_of_empty = [""]
         settings.setValue('zero_value', 0)
         settings.setValue('empty_list', [])
+        settings.setValue('some_strings', sample_list)
+        settings.setValue('string_list_of_empty', string_list_of_empty)
         settings.setValue('bool1', False)
         settings.setValue('bool2', True)
         del settings
@@ -66,6 +70,10 @@ class TestQSettings(unittest.TestCase):
         r = settings.value("variable")
         self.assertEqual(type(r), type(None))
 
+        r = settings.value("variable", type=list)
+        self.assertEqual(type(r), list)
+        self.assertEqual(len(r), 0)
+
         # Handling zero value
         r = settings.value('zero_value')
         self.assertEqual(type(r), int)
@@ -82,6 +90,15 @@ class TestQSettings(unittest.TestCase):
         self.assertTrue(len(r) == 0)
         self.assertEqual(type(r), list)
 
+        r = settings.value('some_strings')
+        self.assertEqual(r, sample_list)
+
+        r = settings.value('some_strings', type=list)
+        self.assertEqual(r, sample_list)
+
+        r = settings.value('string_list_of_empty', type=list)
+        self.assertEqual(r, string_list_of_empty)
+
         # Booleans
         r = settings.value('bool1')
         self.assertEqual(type(r), bool)