Fix MapSnapshotter build failure on Windowsupstream/anderco-win-snapshot

MSVC implementation of std::promise is buggy and only works with types
that can be default-constructed. Wrap LatLngBounds in such a struct to
avoid a compilation failure in the instantiation of ask() inside
MapSnapshotter::getRegion() since that would create a
std::promise<LanLngBounds>.

5 files changed, 42 insertions, 4 deletions

diff --git a/next/platform/linux/linux.cmake b/next/platform/linux/linux.cmake
index 396b9a0ffd..912fbd596c 100644
--- a/next/platform/linux/linux.cmake
+++ b/next/platform/linux/linux.cmake
@@ -17,6 +17,7 @@ target_sources(
         ${MBGL_ROOT}/platform/default/src/mbgl/gl/headless_backend.cpp
         ${MBGL_ROOT}/platform/default/src/mbgl/i18n/collator.cpp
         ${MBGL_ROOT}/platform/default/src/mbgl/i18n/number_format.cpp
+        ${MBGL_ROOT}/platform/default/src/mbgl/map/map_snapshotter.cpp
         ${MBGL_ROOT}/platform/default/src/mbgl/layermanager/layer_manager.cpp
         ${MBGL_ROOT}/platform/default/src/mbgl/storage/asset_file_source.cpp
         ${MBGL_ROOT}/platform/default/src/mbgl/storage/default_file_source.cpp
diff --git a/next/test/CMakeLists.txt b/next/test/CMakeLists.txt
index 4995fa4e56..0da9debaee 100644
--- a/next/test/CMakeLists.txt
+++ b/next/test/CMakeLists.txt
@@ -18,6 +18,7 @@ add_library(
     ${MBGL_ROOT}/test/gl/object.test.cpp
     ${MBGL_ROOT}/test/map/map.test.cpp
     ${MBGL_ROOT}/test/map/prefetch.test.cpp
+    ${MBGL_ROOT}/test/map/snapshotter.test.cpp
     ${MBGL_ROOT}/test/map/transform.test.cpp
     ${MBGL_ROOT}/test/math/clamp.test.cpp
     ${MBGL_ROOT}/test/math/minmax.test.cpp
diff --git a/platform/default/src/mbgl/map/map_snapshotter.cpp b/platform/default/src/mbgl/map/map_snapshotter.cpp
index 705a791af9..0c94eadc33 100644
--- a/platform/default/src/mbgl/map/map_snapshotter.cpp
+++ b/platform/default/src/mbgl/map/map_snapshotter.cpp
@@ -12,6 +12,17 @@
 
 namespace mbgl {
 
+/*
+ * MSVC implementation of std::promise is buggy and only works with types that can be default-constructed.
+ * Wrap LatLngBounds in such a struct to avoid a compilation failure in the instantiation of ask() inside
+ * MapSnapshotter::getRegion() since that would create a std::promise<LanLngBounds>.
+ */
+struct RegionWrapper {
+    explicit RegionWrapper() : region(LatLngBounds::unbounded()) {}
+
+    LatLngBounds region;
+};
+
 class MapSnapshotter::Impl {
 public:
     Impl(const std::pair<bool, std::string> style,
@@ -35,7 +46,7 @@ public:
     CameraOptions getCameraOptions() const;
 
     void setRegion(LatLngBounds);
-    LatLngBounds getRegion() const;
+    RegionWrapper getRegion() const;
 
     void snapshot(ActorRef<MapSnapshotter::Callback>);
 
@@ -157,8 +168,10 @@ void MapSnapshotter::Impl::setRegion(LatLngBounds region) {
     map.jumpTo(map.cameraForLatLngs(latLngs, insets));
 }
 
-LatLngBounds MapSnapshotter::Impl::getRegion() const {
-    return map.latLngBoundsForCamera(getCameraOptions());
+RegionWrapper MapSnapshotter::Impl::getRegion() const {
+    RegionWrapper region;
+    region.region = map.latLngBoundsForCamera(getCameraOptions());
+    return region;
 }
 
 MapSnapshotter::MapSnapshotter(const std::pair<bool, std::string> style,
@@ -215,7 +228,7 @@ void MapSnapshotter::setRegion(const LatLngBounds& bounds) {
 }
 
 LatLngBounds MapSnapshotter::getRegion() const {
-    return impl->actor().ask(&Impl::getRegion).get();
+    return impl->actor().ask(&Impl::getRegion).get().region;
 }
 
 } // namespace mbgl
diff --git a/test/map/snapshotter.test.cpp b/test/map/snapshotter.test.cpp
new file mode 100644
index 0000000000..8e6c8a4904
--- /dev/null
+++ b/test/map/snapshotter.test.cpp
@@ -0,0 +1,22 @@
+#include <mbgl/test/util.hpp>
+
+#include <mbgl/map/camera.hpp>
+#include <mbgl/map/map_snapshotter.hpp>
+#include <mbgl/storage/resource_options.hpp>
+#include <mbgl/util/constants.hpp>
+
+using namespace mbgl;
+
+TEST(Snapshotter, Region) {
+    MapSnapshotter snapshotter({true, "{}"}, {256, 256}, 1.0, {}, {}, {}, {});
+
+    LatLngBounds region = LatLngBounds::hull({1.0, -1.0}, {-1.0, 1.0});
+    snapshotter.setRegion(region);
+
+    LatLngBounds region2 = snapshotter.getRegion();
+
+    EXPECT_NEAR(region.south(), region2.south(), 0.0001);
+    EXPECT_NEAR(region.north(), region2.north(), 0.0001);
+    EXPECT_NEAR(region.east(), region2.east(), 0.0001);
+    EXPECT_NEAR(region.west(), region2.west(), 0.0001);
+}
diff --git a/test/test-files.json b/test/test-files.json
index a98e896e7e..293a0804e2 100644
--- a/test/test-files.json
+++ b/test/test-files.json
@@ -19,6 +19,7 @@
         "test/gl/object.test.cpp",
         "test/map/map.test.cpp",
         "test/map/prefetch.test.cpp",
+        "test/map/snapshotter.test.cpp",
         "test/map/transform.test.cpp",
         "test/math/clamp.test.cpp",
         "test/math/minmax.test.cpp",