[core] Fix layer impl cast in render layer implementations

This PR puts `impl()` functions definitions into a nameless namespace
to provide internal linkage and to make sure that appropriate cast function
is invoked.

src/mbgl/renderer/layers/render_background_layer.cpp

@@ -16,10 +16,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const BackgroundLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == BackgroundLayer::Impl::staticTypeInfo());
     return static_cast<const style::BackgroundLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderBackgroundLayer::RenderBackgroundLayer(Immutable<style::BackgroundLayer::Impl> _impl)
     : RenderLayer(makeMutable<BackgroundLayerProperties>(std::move(_impl))),
       unevaluated(impl(baseImpl).paint.untransitioned()) {

src/mbgl/renderer/layers/render_circle_layer.cpp

@@ -15,10 +15,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const style::CircleLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == CircleLayer::Impl::staticTypeInfo());
     return static_cast<const style::CircleLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderCircleLayer::RenderCircleLayer(Immutable<style::CircleLayer::Impl> _impl)
     : RenderLayer(makeMutable<CircleLayerProperties>(std::move(_impl))),
       unevaluated(impl(baseImpl).paint.untransitioned()) {

src/mbgl/renderer/layers/render_custom_layer.cpp

@@ -14,10 +14,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const CustomLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == CustomLayer::Impl::staticTypeInfo());
     return static_cast<const CustomLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderCustomLayer::RenderCustomLayer(Immutable<style::CustomLayer::Impl> _impl)
     : RenderLayer(makeMutable<CustomLayerProperties>(std::move(_impl))),
       host(impl(baseImpl).host) {

src/mbgl/renderer/layers/render_fill_extrusion_layer.cpp

@@ -20,10 +20,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const FillExtrusionLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == FillExtrusionLayer::Impl::staticTypeInfo());
     return static_cast<const FillExtrusionLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderFillExtrusionLayer::RenderFillExtrusionLayer(Immutable<style::FillExtrusionLayer::Impl> _impl)
     : RenderLayer(makeMutable<FillExtrusionLayerProperties>(std::move(_impl))),
       unevaluated(impl(baseImpl).paint.untransitioned()) {

src/mbgl/renderer/layers/render_fill_layer.cpp

@@ -21,10 +21,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const FillLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == FillLayer::Impl::staticTypeInfo());
     return static_cast<const FillLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderFillLayer::RenderFillLayer(Immutable<style::FillLayer::Impl> _impl)
     : RenderLayer(makeMutable<FillLayerProperties>(std::move(_impl))),
       unevaluated(impl(baseImpl).paint.untransitioned()) {

src/mbgl/renderer/layers/render_heatmap_layer.cpp

@@ -19,10 +19,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const HeatmapLayer::Impl& impl(const Immutable<Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == HeatmapLayer::Impl::staticTypeInfo());
     return static_cast<const HeatmapLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderHeatmapLayer::RenderHeatmapLayer(Immutable<HeatmapLayer::Impl> _impl)
     : RenderLayer(makeMutable<HeatmapLayerProperties>(std::move(_impl))),
     unevaluated(impl(baseImpl).paint.untransitioned()), colorRamp({256, 1}) {

src/mbgl/renderer/layers/render_hillshade_layer.cpp

@@ -18,10 +18,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const HillshadeLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == HillshadeLayer::Impl::staticTypeInfo());
     return static_cast<const HillshadeLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderHillshadeLayer::RenderHillshadeLayer(Immutable<style::HillshadeLayer::Impl> _impl)
     : RenderLayer(makeMutable<HillshadeLayerProperties>(std::move(_impl))),
       unevaluated(impl(baseImpl).paint.untransitioned()) {

src/mbgl/renderer/layers/render_line_layer.cpp

@@ -20,10 +20,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const LineLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == LineLayer::Impl::staticTypeInfo());
     return static_cast<const LineLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderLineLayer::RenderLineLayer(Immutable<style::LineLayer::Impl> _impl)
     : RenderLayer(makeMutable<LineLayerProperties>(std::move(_impl))),
       unevaluated(impl(baseImpl).paint.untransitioned()),

src/mbgl/renderer/layers/render_raster_layer.cpp

@@ -14,10 +14,15 @@ namespace mbgl {
 
 using namespace style;
 
+namespace {
+
 inline const RasterLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == RasterLayer::Impl::staticTypeInfo());
     return static_cast<const RasterLayer::Impl&>(*impl);
 }
 
+} // namespace
+
 RenderRasterLayer::RenderRasterLayer(Immutable<style::RasterLayer::Impl> _impl)
     : RenderLayer(makeMutable<RasterLayerProperties>(std::move(_impl))),
       unevaluated(impl(baseImpl).paint.untransitioned()) {

src/mbgl/renderer/layers/render_symbol_layer.cpp

@@ -227,6 +227,7 @@ void drawText(const DrawFn& draw,
 }
 
 inline const SymbolLayer::Impl& impl(const Immutable<style::Layer::Impl>& impl) {
+    assert(impl->getTypeInfo() == SymbolLayer::Impl::staticTypeInfo());
     return static_cast<const SymbolLayer::Impl&>(*impl);
 }