map-widget: don't crash if the map QML failed to load

If the QML modules for QtLocation and QtPositioning are
missing the QML in mapwidget.cpp will fail to load,
which can lead to crashes.

To solve the issue check if the QML has loaded and set
a flag 'isReady' to true. If the loading has failed
load another QML which is for showing a red error text
in the lines of `MapWidget.qml failed to load!`.

If the map QML has failed, use a macro in all relevant
MapWidget members to turn them into a NOP. This approach
leaves the rest of the codebase intact - e.g. no checks
in classes which connect to the MapWidget class.

Fixes #596

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>

3 files changed, 38 insertions, 5 deletions

diff --git a/desktop-widgets/mapwidget.cpp b/desktop-widgets/mapwidget.cpp
index 34f7ed217..806b82c2d 100644
--- a/desktop-widgets/mapwidget.cpp
+++ b/desktop-widgets/mapwidget.cpp
@@ -12,8 +12,14 @@
 #include "mainwindow.h"
 #include "divelistview.h"
 
+static const QUrl urlMapWidget = QUrl(QStringLiteral("qrc:/MapWidget.qml"));
+static const QUrl urlMapWidgetError = QUrl(QStringLiteral("qrc:/MapWidgetError.qml"));
+static bool isReady = false;
 static bool skipReload = false;
 
+#define CHECK_IS_READY_RETURN_VOID() \
+	if (!isReady) return
+
 MapWidget *MapWidget::m_instance = NULL;
 
 MapWidget::MapWidget(QWidget *parent) : QQuickWidget(parent)
@@ -22,19 +28,23 @@ MapWidget::MapWidget(QWidget *parent) : QQuickWidget(parent)
 	qmlRegisterType<MapLocationModel>("org.subsurfacedivelog.mobile", 1, 0, "MapLocationModel");
 	qmlRegisterType<MapLocation>("org.subsurfacedivelog.mobile", 1, 0, "MapLocation");
 
+	setResizeMode(QQuickWidget::SizeRootObjectToView);
 	connect(this, &QQuickWidget::statusChanged, this, &MapWidget::doneLoading);
-	setSource(QUrl(QStringLiteral("qrc:/MapWidget.qml")));
+	setSource(urlMapWidget);
 }
 
 void MapWidget::doneLoading(QQuickWidget::Status status)
 {
-	if (status != QQuickWidget::Ready) {
-		qDebug() << "MapWidget status" << status;
+	// the default map widget QML failed; load the error QML.
+	if (source() == urlMapWidget && status != QQuickWidget::Ready) {
+		qDebug() << urlMapWidget << "failed to load with status:" << status;
+		setSource(urlMapWidgetError);
+		return;
+	} else if (source() == urlMapWidgetError) { // the error QML finished loading.
 		return;
 	}
-	qDebug() << "MapWidget ready";
-	setResizeMode(QQuickWidget::SizeRootObjectToView);
 
+	isReady = true;
 	m_rootItem = qobject_cast<QQuickItem *>(rootObject());
 	m_mapHelper = rootObject()->findChild<MapWidgetHelper *>();
 	connect(m_mapHelper, SIGNAL(selectedDivesChanged(QList<int>)),
@@ -45,12 +55,14 @@ void MapWidget::doneLoading(QQuickWidget::Status status)
 
 void MapWidget::centerOnDiveSite(struct dive_site *ds)
 {
+	CHECK_IS_READY_RETURN_VOID();
 	if (!skipReload)
 		m_mapHelper->centerOnDiveSite(ds);
 }
 
 void MapWidget::centerOnIndex(const QModelIndex& idx)
 {
+	CHECK_IS_READY_RETURN_VOID();
 	struct dive_site *ds = get_dive_site_by_uuid(idx.model()->index(idx.row(), 0).data().toInt());
 	if (!ds || !dive_site_has_gps_location(ds))
 		centerOnDiveSite(&displayed_dive_site);
@@ -60,11 +72,13 @@ void MapWidget::centerOnIndex(const QModelIndex& idx)
 
 void MapWidget::repopulateLabels()
 {
+	CHECK_IS_READY_RETURN_VOID();
 	m_mapHelper->reloadMapLocations();
 }
 
 void MapWidget::reload()
 {
+	CHECK_IS_READY_RETURN_VOID();
 	setEditMode(false);
 	if (!skipReload)
 		m_mapHelper->reloadMapLocations();
@@ -72,21 +86,25 @@ void MapWidget::reload()
 
 void MapWidget::setEditMode(bool editMode)
 {
+	CHECK_IS_READY_RETURN_VOID();
 	m_mapHelper->setEditMode(editMode);
 }
 
 void MapWidget::endGetDiveCoordinates()
 {
+	CHECK_IS_READY_RETURN_VOID();
 	setEditMode(false);
 }
 
 void MapWidget::prepareForGetDiveCoordinates()
 {
+	CHECK_IS_READY_RETURN_VOID();
 	setEditMode(true);
 }
 
 void MapWidget::selectedDivesChanged(QList<int> list)
 {
+	CHECK_IS_READY_RETURN_VOID();
 	skipReload = true;
 	MainWindow::instance()->dive_list()->unselectDives();
 	if (!list.empty())
@@ -96,6 +114,7 @@ void MapWidget::selectedDivesChanged(QList<int> list)
 
 void MapWidget::coordinatesChangedLocal()
 {
+	CHECK_IS_READY_RETURN_VOID();
 	emit coordinatesChanged();
 }
 
diff --git a/mobile-widgets/qml/MapWidgetError.qml b/mobile-widgets/qml/MapWidgetError.qml
new file mode 100644
index 000000000..346e95f07
--- /dev/null
+++ b/mobile-widgets/qml/MapWidgetError.qml
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+import QtQuick 2.0
+
+Item {
+	Text {
+		anchors.fill: parent
+		horizontalAlignment: Text.AlignHCenter
+		verticalAlignment: Text.AlignVCenter
+		color: "red"
+		text: qsTr("MapWidget.qml failed to load!
+The QML modules QtPositioning and QtLocation could be missing!")
+	}
+}
diff --git a/subsurface.qrc b/subsurface.qrc
index e5f75d1e3..fc4e2ce6c 100644
--- a/subsurface.qrc
+++ b/subsurface.qrc
@@ -1,6 +1,7 @@
 <RCC>
     <qresource prefix="/">
         <file alias="MapWidget.qml">mobile-widgets/qml/MapWidget.qml</file>
+        <file alias="MapWidgetError.qml">mobile-widgets/qml/MapWidgetError.qml</file>
         <file alias="MapWidgetContextMenu.qml">mobile-widgets/qml/MapWidgetContextMenu.qml</file>
         <file alias="mapwidget-marker">mobile-widgets/qml/icons/mapwidget-marker.png</file>
         <file alias="mapwidget-marker-selected">mobile-widgets/qml/icons/mapwidget-marker-selected.png</file>