[core] Check if style exists prior to accessing via Map functions

src/mbgl/map/map.cpp

@@ -761,26 +761,40 @@ AnnotationIDs Map::queryPointAnnotations(const ScreenBox& box) {
 #pragma mark - Style API
 
 style::Source* Map::getSource(const std::string& sourceID) {
-    impl->styleMutated = true;
-    return impl->style ? impl->style->getSource(sourceID) : nullptr;
+    if (impl->style) {
+        impl->styleMutated = true;
+        return impl->style->getSource(sourceID);
+    }
+    return nullptr;
 }
 
 void Map::addSource(std::unique_ptr<style::Source> source) {
-    impl->styleMutated = true;
-    impl->style->addSource(std::move(source));
+    if (impl->style) {
+        impl->styleMutated = true;
+        impl->style->addSource(std::move(source));
+    }
 }
 
 void Map::removeSource(const std::string& sourceID) {
-    impl->styleMutated = true;
-    impl->style->removeSource(sourceID);
+    if (impl->style) {
+        impl->styleMutated = true;
+        impl->style->removeSource(sourceID);
+    }
 }
 
 style::Layer* Map::getLayer(const std::string& layerID) {
-    impl->styleMutated = true;
-    return impl->style ? impl->style->getLayer(layerID) : nullptr;
+    if (impl->style) {
+        impl->styleMutated = true;
+        return impl->style->getLayer(layerID);
+    }
+    return nullptr;
 }
 
 void Map::addLayer(std::unique_ptr<Layer> layer, const optional<std::string>& before) {
+    if (!impl->style) {
+        return;
+    }
+
     impl->styleMutated = true;
     impl->view.activate();
 
@@ -792,6 +806,10 @@ void Map::addLayer(std::unique_ptr<Layer> layer, const optional<std::string>& be
 }
 
 void Map::removeLayer(const std::string& id) {
+    if (!impl->style) {
+        return;
+    }
+
     impl->styleMutated = true;
     impl->view.activate();
 
@@ -805,23 +823,38 @@ void Map::removeLayer(const std::string& id) {
 #pragma mark - Defaults
 
 std::string Map::getStyleName() const {
-    return impl->style->getName();
+    if (impl->style) {
+        return impl->style->getName();
+    }
+    return {};
 }
 
 LatLng Map::getDefaultLatLng() const {
-    return impl->style->getDefaultLatLng();
+    if (impl->style) {
+        return impl->style->getDefaultLatLng();
+    }
+    return {};
 }
 
 double Map::getDefaultZoom() const {
-    return impl->style->getDefaultZoom();
+    if (impl->style) {
+        return impl->style->getDefaultZoom();
+    }
+    return {};
 }
 
 double Map::getDefaultBearing() const {
-    return impl->style->getDefaultBearing();
+    if (impl->style) {
+        return impl->style->getDefaultBearing();
+    }
+    return {};
 }
 
 double Map::getDefaultPitch() const {
-    return impl->style->getDefaultPitch();
+    if (impl->style) {
+        return impl->style->getDefaultPitch();
+    }
+    return {};
 }
 
 #pragma mark - Toggles
@@ -860,32 +893,37 @@ MapDebugOptions Map::getDebug() const {
 }
 
 bool Map::isFullyLoaded() const {
-    return impl->style->isLoaded();
+    return impl->style ? impl->style->isLoaded() : false;
 }
 
 void Map::addClass(const std::string& className, const TransitionOptions& properties) {
-    if (impl->style->addClass(className, properties)) {
+    if (impl->style && impl->style->addClass(className, properties)) {
         update(Update::Classes);
     }
 }
 
 void Map::removeClass(const std::string& className, const TransitionOptions& properties) {
-    if (impl->style->removeClass(className, properties)) {
+    if (impl->style && impl->style->removeClass(className, properties)) {
         update(Update::Classes);
     }
 }
 
 void Map::setClasses(const std::vector<std::string>& classNames, const TransitionOptions& properties) {
-    impl->style->setClasses(classNames, properties);
-    update(Update::Classes);
+    if (impl->style) {
+        impl->style->setClasses(classNames, properties);
+        update(Update::Classes);
+    }
 }
 
 bool Map::hasClass(const std::string& className) const {
-    return impl->style->hasClass(className);
+    return impl->style ? impl->style->hasClass(className) : false;
 }
 
 std::vector<std::string> Map::getClasses() const {
-    return impl->style->getClasses();
+    if (impl->style) {
+        return impl->style->getClasses();
+    }
+    return {};
 }
 
 void Map::setSourceTileCacheSize(size_t size) {