Add reserve()/capacity() to contiguous opaque containers

Generate bindings for reserve()/capacity() if the container
supports it.

[ChangeLog][shiboken6] Bindings for reserve()/capacity() were
added to contiguous opaque containers.

Task-number: PYSIDE-1605
Change-Id: I82dd2efc4a1831600aa2fae9427e5d13a67cdd11
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
(cherry picked from commit 683314b3491dea17f0205baa2976e71595ccb05d)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

4 files changed, 64 insertions, 0 deletions

diff --git a/examples/widgets/painting/plot/plot.py b/examples/widgets/painting/plot/plot.py
index 156a6408d..a125c3253 100644
--- a/examples/widgets/painting/plot/plot.py
+++ b/examples/widgets/painting/plot/plot.py
@@ -63,6 +63,7 @@ class PlotWidget(QWidget):
         self._timer.timeout.connect(self.shift)
 
         self._points = QPointList()
+        self._points.reserve(WIDTH)
         self._x = 0
         self._delta_x = 0.05
         self._half_height = HEIGHT / 2
diff --git a/sources/shiboken6/doc/typesystem_containers.rst b/sources/shiboken6/doc/typesystem_containers.rst
index ac22df558..c3a60a707 100644
--- a/sources/shiboken6/doc/typesystem_containers.rst
+++ b/sources/shiboken6/doc/typesystem_containers.rst
@@ -47,3 +47,15 @@ the STL and the Qt naming convention (which resembles Python's) are supported:
     +-------------------------------------------+-----------------------------------+
     | ``pop_front()``, ``removeFirst()``        | Removes the first element.        |
     +-------------------------------------------+-----------------------------------+
+    | ``reserve(size)``                         | For containers that support it    |
+    |                                           | (``std::vector``, ``QList``),     |
+    |                                           | allocate memory for at least      |
+    |                                           | ``size`` elements, preventing     |
+    |                                           | reallocations.                    |
+    +-------------------------------------------+-----------------------------------+
+    | ``capacity()``                            | For containers that support it    |
+    |                                           | (``std::vector``, ``QList``),     |
+    |                                           | return the number of elements     |
+    |                                           | that can be stored without        |
+    |                                           | reallocation.                     |
+    +-------------------------------------------+-----------------------------------+
diff --git a/sources/shiboken6/generator/shiboken/cppgenerator_container.cpp b/sources/shiboken6/generator/shiboken/cppgenerator_container.cpp
index 1fa7fc463..7d20d2f16 100644
--- a/sources/shiboken6/generator/shiboken/cppgenerator_container.cpp
+++ b/sources/shiboken6/generator/shiboken/cppgenerator_container.cpp
@@ -175,6 +175,8 @@ CppGenerator::OpaqueContainerData
         writeNoArgsMethod(s, privateObjType, "pop_front");
         writeMethod(s, privateObjType, "pop_front", "removeFirst"); // Qt convention
     }
+    writeMethod(s, privateObjType, "reserve");
+    writeNoArgsMethod(s, privateObjType, "capacity");
     s << "{nullptr, nullptr, 0, nullptr} // Sentinel\n"
         << outdent << "};\n\n";
 
diff --git a/sources/shiboken6/libshiboken/sbkcontainer.h b/sources/shiboken6/libshiboken/sbkcontainer.h
index 97062a198..65bb8646e 100644
--- a/sources/shiboken6/libshiboken/sbkcontainer.h
+++ b/sources/shiboken6/libshiboken/sbkcontainer.h
@@ -67,6 +67,21 @@ struct ShibokenContainerValueConverter
     static std::optional<Value> convertValueToCpp(PyObject pyArg);
 };
 
+// SFINAE test for the presence of reserve() in a sequence container (std::vector/QList)
+template <typename T>
+class ShibokenContainerHasReserve
+{
+private:
+    using YesType = char[1];
+    using NoType = char[2];
+
+    template <typename C> static YesType& test( decltype(&C::reserve) ) ;
+    template <typename C> static NoType& test(...);
+
+public:
+    enum { value = sizeof(test<T>(nullptr)) == sizeof(YesType) };
+};
+
 template <class SequenceContainer>
 class ShibokenSequenceContainerPrivate // Helper for sequence type containers
 {
@@ -212,6 +227,40 @@ public:
         Py_RETURN_NONE;
     }
 
+    // Support for containers with reserve/capacity
+    static PyObject *reserve(PyObject *self, PyObject *pyArg)
+    {
+        auto *d = get(self);
+        if (PyLong_Check(pyArg) == 0) {
+            PyErr_SetString(PyExc_TypeError, "wrong type passed to reserve().");
+            return nullptr;
+        }
+        if (d->m_const) {
+            PyErr_SetString(PyExc_TypeError, msgModifyConstContainer);
+            return nullptr;
+        }
+
+        if constexpr (ShibokenContainerHasReserve<SequenceContainer>::value) {
+            const Py_ssize_t size = PyLong_AsSsize_t(pyArg);
+            d->m_list->reserve(size);
+        } else {
+            PyErr_SetString(PyExc_TypeError, "Container does not support reserve().");
+            return nullptr;
+        }
+
+        Py_RETURN_NONE;
+    }
+
+    static PyObject *capacity(PyObject *self)
+    {
+        Py_ssize_t result = -1;
+        if constexpr (ShibokenContainerHasReserve<SequenceContainer>::value) {
+            const auto *d = get(self);
+            result = d->m_list->capacity();
+        }
+        return PyLong_FromSsize_t(result);
+    }
+
     static ShibokenSequenceContainerPrivate *get(PyObject *self)
     {
         auto *data = reinterpret_cast<ShibokenContainer *>(self);