[core] TileData objects now store whether an optional load attempt was performed

src/mbgl/tile/file_based_tile_source_impl.hpp

@@ -40,6 +40,8 @@ void FileBasedTileSource<T, I>::loadOptional() {
     request = fileSource.request(resource, [this](Response res) {
         request.reset();
 
+        T::tileData.setTriedOptional();
+
         if (res.error && res.error->reason == Response::Error::Reason::NotFound) {
             // When the optional request could not be satisfied, don't treat it as an error.
             // Instead, we make sure that the next request knows that there has been an optional

src/mbgl/tile/tile_data.cpp

@@ -24,6 +24,11 @@ void TileData::setTileSource(std::unique_ptr<TileSource> tileSource_) {
     tileSource = std::move(tileSource_);
 }
 
+void TileData::setTriedOptional() {
+    triedOptional = true;
+    observer->onNeedsRepaint();
+}
+
 void TileData::dumpDebugLogs() const {
     Log::Info(Event::General, "TileData::id: %s", util::toString(id).c_str());
     Log::Info(Event::General, "TileData::renderable: %s", isRenderable() ? "yes" : "no");

src/mbgl/tile/tile_data.hpp

@@ -50,6 +50,14 @@ public:
             const TransformState&,
             const optional<std::vector<std::string>>& layerIDs);
 
+    void setTriedOptional();
+
+    // Returns true when the tile source has received a first response, regardless of whether a load
+    // error occurred or actual data was loaded.
+    bool hasTriedOptional() const {
+        return triedOptional;
+    }
+
     // Tile data considered "Renderable" can be used for rendering. Data in
     // partial state is still waiting for network resources but can also
     // be rendered, although layers will be missing.
@@ -74,6 +82,8 @@ public:
     std::unique_ptr<DebugBucket> debugBucket;
 
 protected:
+    bool triedOptional = false;
+
     enum class DataAvailability : uint8_t {
         // Still waiting for data to load or parse.
         None,

test/algorithm/mock.hpp

@@ -29,11 +29,17 @@ struct MockBucket {};
 
 struct MockTileData {
     MockTileData(const mbgl::OverscaledTileID& tileID_) : tileID(tileID_) {}
-    bool isRenderable() {
+
+    bool hasTriedOptional() const {
+        return triedOptional;
+    }
+
+    bool isRenderable() const {
         return renderable;
     }
 
     bool renderable = false;
+    bool triedOptional = false;
     const mbgl::OverscaledTileID tileID;
 };