Fix pure virtual function call v2 (#3996)

Author: adrian-cojocaru

src/mbgl/tile/vector_mlt_tile.cpp

@@ -16,6 +16,9 @@ VectorMLTTile::VectorMLTTile(const OverscaledTileID& id_,
     : VectorTile(id_, std::move(sourceID_), parameters_, tileset_, observer_) {}
 
 VectorMLTTile::~VectorMLTTile() {
+    // this needs to be explicitly deleted in the most-derived destructor
+    loader.reset();
+
     // Don't rely on `~TileLoader` to close, it's not safe to call there.
     // We're still calling a virtual method from a destructor, so any overrides will not be called.
     GeometryTile::cancel();

src/mbgl/tile/vector_mlt_tile.hpp

@@ -9,7 +9,7 @@ namespace mbgl {
 class Tileset;
 class TileParameters;
 
-class VectorMLTTile : public VectorTile {
+class VectorMLTTile final : public VectorTile {
 public:
     VectorMLTTile(const OverscaledTileID&,
                   std::string sourceID,

src/mbgl/tile/vector_mvt_tile.cpp

@@ -16,6 +16,9 @@ VectorMVTTile::VectorMVTTile(const OverscaledTileID& id_,
     : VectorTile(id_, std::move(sourceID_), parameters_, tileset_, observer_) {}
 
 VectorMVTTile::~VectorMVTTile() {
+    // this needs to be explicitly deleted in the most-derived destructor
+    loader.reset();
+
     // Don't rely on `~TileLoader` to close, it's not safe to call there.
     // We're still calling a virtual method from a destructor, so any overrides will not be called.
     GeometryTile::cancel();

src/mbgl/tile/vector_mvt_tile.hpp

@@ -9,7 +9,7 @@ namespace mbgl {
 class Tileset;
 class TileParameters;
 
-class VectorMVTTile : public VectorTile {
+class VectorMVTTile final : public VectorTile {
 public:
     VectorMVTTile(const OverscaledTileID&,
                   std::string sourceID,

src/mbgl/tile/vector_tile.cpp

@@ -13,20 +13,16 @@ VectorTile::VectorTile(const OverscaledTileID& id_,
                        const Tileset& tileset,
                        TileObserver* observer_)
     : GeometryTile(id_, std::move(sourceID_), parameters_, observer_),
-      loader(*this, id_, parameters_, tileset) {}
+      loader(std::make_unique<TileLoader<VectorTile>>(*this, id_, parameters_, tileset)) {}
 
-VectorTile::~VectorTile() {
-    // Don't rely on `~TileLoader` to close, it's not safe to call there.
-    // We're still calling a virtual method from a destructor, so any overrides will not be called.
-    GeometryTile::cancel();
-}
+VectorTile::~VectorTile() {}
 
 void VectorTile::setNecessity(TileNecessity necessity) {
-    loader.setNecessity(necessity);
+    loader->setNecessity(necessity);
 }
 
 void VectorTile::setUpdateParameters(const TileUpdateParameters& params) {
-    loader.setUpdateParameters(params);
+    loader->setUpdateParameters(params);
 }
 
 void VectorTile::setMetadata(std::optional<Timestamp> modified_, std::optional<Timestamp> expires_) {

src/mbgl/tile/vector_tile.hpp

@@ -23,8 +23,10 @@ class VectorTile : public GeometryTile {
 
     virtual void setData(const std::shared_ptr<const std::string>&) = 0;
 
-private:
-    TileLoader<VectorTile> loader;
+protected:
+    // this needs to be explicitly deleted in the most-derived destructor
+    // see `~VectorMVTTile`
+    std::unique_ptr<TileLoader<VectorTile>> loader;
 };
 
 } // namespace mbgl