GStreamer: introduce GList range adaptor

Remove boilerplate code when iterating GLists.

Pick-to: 6.5
Change-Id: I66603585e51b27f2302d83a08e03ba104871232a
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit 40bb9be18b0e249dee430eb72539309331fb35f0)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 1ef7349ccefa27e68b5e18322872e38c9c4b0eb6)

4 files changed, 111 insertions, 40 deletions

diff --git a/src/plugins/multimedia/gstreamer/common/qglist_helper_p.h b/src/plugins/multimedia/gstreamer/common/qglist_helper_p.h
new file mode 100644
index 000000000..54108e1c3
--- /dev/null
+++ b/src/plugins/multimedia/gstreamer/common/qglist_helper_p.h
@@ -0,0 +1,82 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QGLIST_HELPER_P_H
+#define QGLIST_HELPER_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists purely as an
+// implementation detail. This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qtconfigmacros.h>
+
+#include <glib.h>
+#include <iterator>
+
+QT_BEGIN_NAMESPACE
+
+namespace QGstUtils {
+
+template <typename ListType>
+struct GListIterator
+{
+    explicit GListIterator(const GList *element = nullptr) : element(element) { }
+
+    const ListType &operator*() const noexcept { return *operator->(); }
+    const ListType *operator->() const noexcept
+    {
+        return reinterpret_cast<const ListType *>(&element->data);
+    }
+
+    GListIterator &operator++() noexcept
+    {
+        if (element)
+            element = element->next;
+
+        return *this;
+    }
+    GListIterator operator++(int n) noexcept
+    {
+        for (int i = 0; i != n; ++i)
+            operator++();
+
+        return *this;
+    }
+
+    bool operator==(const GListIterator &r) const noexcept { return element == r.element; }
+    bool operator!=(const GListIterator &r) const noexcept { return element != r.element; }
+
+    using difference_type = std::ptrdiff_t;
+    using value_type = ListType;
+    using pointer = value_type *;
+    using reference = value_type &;
+    using iterator_category = std::input_iterator_tag;
+
+    const GList *element = nullptr;
+};
+
+template <typename ListType>
+struct GListRangeAdaptor
+{
+    static_assert(std::is_pointer_v<ListType>);
+
+    explicit GListRangeAdaptor(const GList *list) : head(list) { }
+
+    auto begin() { return GListIterator<ListType>(head); }
+    auto end() { return GListIterator<ListType>(nullptr); }
+
+    const GList *head;
+};
+
+} // namespace QGstUtils
+
+QT_END_NAMESPACE
+
+#endif
diff --git a/src/plugins/multimedia/gstreamer/common/qgstreamervideooverlay.cpp b/src/plugins/multimedia/gstreamer/common/qgstreamervideooverlay.cpp
index b6d0de876..3def5f515 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstreamervideooverlay.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgstreamervideooverlay.cpp
@@ -4,10 +4,11 @@
 #include "qgstreamervideooverlay_p.h"
 
 #include <QtGui/qguiapplication.h>
-#include "qgstutils_p.h"
+#include "qglist_helper_p.h"
 #include "qgst_p.h"
 #include "qgstreamermessage_p.h"
 #include "qgstreamervideosink_p.h"
+#include "qgstutils_p.h"
 
 #include <gst/video/videooverlay.h>
 
@@ -67,9 +68,7 @@ static QGstElement findBestVideoSink()
     // If none of the known video sinks are available, try to find one that implements the
     // GstVideoOverlay interface and has autoplugging rank.
     GList *list = qt_gst_video_sinks();
-    for (GList *item = list; item != nullptr; item = item->next) {
-        GstElementFactory *f = GST_ELEMENT_FACTORY(item->data);
-
+    for (GstElementFactory *f : QGstUtils::GListRangeAdaptor<GstElementFactory *>(list)) {
         if (!gst_element_factory_has_interface(f, "GstVideoOverlay"))
             continue;
 
diff --git a/src/plugins/multimedia/gstreamer/qgstreamerformatinfo.cpp b/src/plugins/multimedia/gstreamer/qgstreamerformatinfo.cpp
index 70a824c8b..45291b7a6 100644
--- a/src/plugins/multimedia/gstreamer/qgstreamerformatinfo.cpp
+++ b/src/plugins/multimedia/gstreamer/qgstreamerformatinfo.cpp
@@ -1,6 +1,7 @@
 // Copyright (C) 2021 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
+#include "qglist_helper_p.h"
 #include "qgstreamerformatinfo_p.h"
 
 QT_BEGIN_NAMESPACE
@@ -143,16 +144,11 @@ static QPair<QList<QMediaFormat::AudioCodec>, QList<QMediaFormat::VideoCodec>> g
     GList *elementList = gst_element_factory_list_get_elements(decode ? GST_ELEMENT_FACTORY_TYPE_DECODER : GST_ELEMENT_FACTORY_TYPE_ENCODER,
                                                                GST_RANK_MARGINAL);
 
-    GList *element = elementList;
-    while (element) {
-        GstElementFactory *factory = (GstElementFactory *)element->data;
-        element = element->next;
-
-        const GList *padTemplates = gst_element_factory_get_static_pad_templates(factory);
-        while (padTemplates) {
-            GstStaticPadTemplate *padTemplate = (GstStaticPadTemplate *)padTemplates->data;
-            padTemplates = padTemplates->next;
-
+    for (GstElementFactory *factory :
+         QGstUtils::GListRangeAdaptor<GstElementFactory *>(elementList)) {
+        for (GstStaticPadTemplate *padTemplate :
+             QGstUtils::GListRangeAdaptor<GstStaticPadTemplate *>(
+                     gst_element_factory_get_static_pad_templates(factory))) {
             if (padTemplate->direction == padDirection) {
                 auto caps = QGstCaps(gst_static_caps_get(&padTemplate->static_caps), QGstCaps::HasRef);
 
@@ -181,19 +177,17 @@ QList<QGstreamerFormatInfo::CodecMap> QGstreamerFormatInfo::getMuxerList(bool de
 
     GstPadDirection padDirection = demuxer ? GST_PAD_SINK : GST_PAD_SRC;
 
-    GList *elementList = gst_element_factory_list_get_elements(demuxer ? GST_ELEMENT_FACTORY_TYPE_DEMUXER : GST_ELEMENT_FACTORY_TYPE_MUXER,
-                                                               GST_RANK_MARGINAL);
-    GList *element = elementList;
-    while (element) {
-        GstElementFactory *factory = (GstElementFactory *)element->data;
-        element = element->next;
+    GList *elementList = gst_element_factory_list_get_elements(
+            demuxer ? GST_ELEMENT_FACTORY_TYPE_DEMUXER : GST_ELEMENT_FACTORY_TYPE_MUXER,
+            GST_RANK_MARGINAL);
 
+    for (GstElementFactory *factory :
+         QGstUtils::GListRangeAdaptor<GstElementFactory *>(elementList)) {
         QList<QMediaFormat::FileFormat> fileFormats;
 
-        const GList *padTemplates = gst_element_factory_get_static_pad_templates(factory);
-        while (padTemplates) {
-            GstStaticPadTemplate *padTemplate = (GstStaticPadTemplate *)padTemplates->data;
-            padTemplates = padTemplates->next;
+        for (GstStaticPadTemplate *padTemplate :
+             QGstUtils::GListRangeAdaptor<GstStaticPadTemplate *>(
+                     gst_element_factory_get_static_pad_templates(factory))) {
 
             if (padTemplate->direction == padDirection) {
                 auto caps = QGstCaps(gst_static_caps_get(&padTemplate->static_caps), QGstCaps::HasRef);
@@ -212,10 +206,9 @@ QList<QGstreamerFormatInfo::CodecMap> QGstreamerFormatInfo::getMuxerList(bool de
         QList<QMediaFormat::AudioCodec> audioCodecs;
         QList<QMediaFormat::VideoCodec> videoCodecs;
 
-        padTemplates = gst_element_factory_get_static_pad_templates(factory);
-        while (padTemplates) {
-            GstStaticPadTemplate *padTemplate = (GstStaticPadTemplate *)padTemplates->data;
-            padTemplates = padTemplates->next;
+        for (GstStaticPadTemplate *padTemplate :
+             QGstUtils::GListRangeAdaptor<GstStaticPadTemplate *>(
+                     gst_element_factory_get_static_pad_templates(factory))) {
 
             // check the other side for supported inputs/outputs
             if (padTemplate->direction != padDirection) {
@@ -275,16 +268,12 @@ static QList<QImageCapture::FileFormat> getImageFormatList()
     GList *elementList = gst_element_factory_list_get_elements(GST_ELEMENT_FACTORY_TYPE_ENCODER,
                                                                GST_RANK_MARGINAL);
 
-    GList *element = elementList;
-    while (element) {
-        GstElementFactory *factory = (GstElementFactory *)element->data;
-        element = element->next;
-
-        const GList *padTemplates = gst_element_factory_get_static_pad_templates(factory);
-        while (padTemplates) {
-            GstStaticPadTemplate *padTemplate = (GstStaticPadTemplate *)padTemplates->data;
-            padTemplates = padTemplates->next;
+    for (GstElementFactory *factory :
+         QGstUtils::GListRangeAdaptor<GstElementFactory *>(elementList)) {
 
+        for (GstStaticPadTemplate *padTemplate :
+             QGstUtils::GListRangeAdaptor<GstStaticPadTemplate *>(
+                     gst_element_factory_get_static_pad_templates(factory))) {
             if (padTemplate->direction == GST_PAD_SRC) {
                 QGstCaps caps = QGstCaps(gst_static_caps_get(&padTemplate->static_caps), QGstCaps::HasRef);
 
diff --git a/src/plugins/multimedia/gstreamer/qgstreamervideodevices.cpp b/src/plugins/multimedia/gstreamer/qgstreamervideodevices.cpp
index 799fa8792..ddb5fe605 100644
--- a/src/plugins/multimedia/gstreamer/qgstreamervideodevices.cpp
+++ b/src/plugins/multimedia/gstreamer/qgstreamervideodevices.cpp
@@ -6,6 +6,7 @@
 #include "private/qcameradevice_p.h"
 
 #include "qgstutils_p.h"
+#include "qglist_helper_p.h"
 
 QT_BEGIN_NAMESPACE
 
@@ -46,14 +47,14 @@ QGstreamerVideoDevices::QGstreamerVideoDevices(QPlatformMediaIntegration *integr
 
     GList *devices = gst_device_monitor_get_devices(m_deviceMonitor.get());
 
-    while (devices) {
-        GstDevice *device = static_cast<GstDevice *>(devices->data);
+    for (GstDevice *device : QGstUtils::GListRangeAdaptor<GstDevice *>(devices)) {
         addDevice(QGstDeviceHandle{
                 device,
                 QGstDeviceHandle::HasRef,
         });
-        devices = g_list_delete_link(devices, devices);
     }
+
+    g_list_free(devices);
 }
 
 QGstreamerVideoDevices::~QGstreamerVideoDevices()