[core] add MapChangeDidFinishLoadingStyle signal (#6371)

src/mbgl/map/change.hpp

@@ -19,6 +19,7 @@ enum MapChange : uint8_t {
     MapChangeWillStartRenderingMap = 11,
     MapChangeDidFinishRenderingMap = 12,
     MapChangeDidFinishRenderingMapFullyRendered = 13,
+    MapChangeDidFinishLoadingStyle = 14
 };
 
 } // namespace mbgl

src/mbgl/map/map.cpp

@@ -39,6 +39,7 @@ public:
     Impl(View&, FileSource&, MapMode, GLContextMode, ConstrainMode, ViewportMode);
 
     void onUpdate(Update) override;
+    void onStyleLoaded() override;
     void onStyleError() override;
     void onResourceError(std::exception_ptr) override;
 
@@ -965,6 +966,10 @@ void Map::Impl::onUpdate(Update flags) {
     updateFlags |= flags;
     asyncUpdate.send();
 }
+    
+void Map::Impl::onStyleLoaded() {
+    view.notifyMapChange(MapChangeDidFinishLoadingStyle);
+}
 
 void Map::Impl::onStyleError() {
     view.notifyMapChange(MapChangeDidFailLoadingMap);

src/mbgl/style/observer.hpp

@@ -14,6 +14,7 @@ class Observer : public GlyphAtlasObserver,
 public:
     virtual void onUpdate(Update) {}
     virtual void onStyleError() {}
+    virtual void onStyleLoaded() {}
     virtual void onResourceError(std::exception_ptr) {}
 };
 

src/mbgl/style/style.cpp

@@ -105,6 +105,8 @@ void Style::setJSON(const std::string& json) {
         observer->onResourceError(error);
 
         return;
+    } else {
+        observer->onStyleLoaded();
     }
 
     for (auto& source : parser.sources) {

test/map/map.cpp

@@ -202,6 +202,26 @@ TEST(Map, StyleEarlyMutation) {
     EXPECT_NE(nullptr, map.getLayer("water"));
 }
 
+TEST(Map, StyleLoadedSignal) {
+    MapTest test;
+    Map map(test.view, test.fileSource, MapMode::Still);
+    
+    // The map should emit a signal on style loaded
+    bool emitted = false;
+    test.view.setMapChangeCallback([&](MapChange change) {
+        if (change == mbgl::MapChangeDidFinishLoadingStyle) {
+            emitted = true;
+        }
+    });
+    map.setStyleJSON(util::read_file("test/fixtures/api/empty.json"));
+    EXPECT_TRUE(emitted);
+    
+    // But not when the style couldn't be parsed
+    emitted = false;
+    map.setStyleJSON("invalid");
+    EXPECT_FALSE(emitted);
+}
+
 TEST(Map, AddLayer) {
     MapTest test;