[android] Fix implicit geometry conversions for NDK r13b

platform/android/src/geojson/multi_point.cpp

@@ -2,6 +2,8 @@
 
 #include "line_string.hpp"
 
+#include "util.hpp"
+
 namespace mbgl {
 namespace android {
 namespace geojson {
@@ -11,7 +13,7 @@ mapbox::geojson::multi_point MultiPoint::convert(jni::JNIEnv &env, jni::Object<M
 
     if (jMultiPoint) {
         auto jPositionListsList = MultiPoint::getCoordinates(env, jMultiPoint);
-        multiPoint = LineString::convert(env, jPositionListsList);
+        multiPoint = convertExplicit<mapbox::geojson::multi_point>(LineString::convert(env, jPositionListsList));
         jni::DeleteLocalRef(env, jPositionListsList);
     }
 

platform/android/src/geojson/polygon.cpp

@@ -2,6 +2,8 @@
 
 #include "multi_line_string.hpp"
 
+#include "util.hpp"
+
 namespace mbgl {
 namespace android {
 namespace geojson {
@@ -24,7 +26,9 @@ mapbox::geojson::polygon Polygon::convert(jni::JNIEnv &env, jni::Object<java::ut
     if (jPositionListsList) {
         auto multiLine = MultiLineString::convert(env, jPositionListsList);
         polygon.reserve(multiLine.size());
-        polygon.insert(std::end(polygon), std::begin(multiLine), std::end(multiLine));
+        for (auto&& line : multiLine) {
+            polygon.emplace_back(convertExplicit<mapbox::geojson::linear_ring>(std::move(line)));
+        }
     }
 
     return polygon;

platform/android/src/geojson/util.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <type_traits>
+
+namespace mbgl {
+namespace android {
+namespace geojson {
+
+// Clang 3.8 fails to implicitly convert matching types, so we'll have to do it explicitly.
+template <typename To, typename From>
+To convertExplicit(From&& src) {
+    static_assert(std::is_same<typename std::decay_t<From>::container_type,
+                               typename To::container_type>::value,
+                  "container types do not match");
+    static_assert(std::is_rvalue_reference<From&&>::value,
+                  "argument must be rvalue reference");
+    return *reinterpret_cast<std::add_pointer_t<To>>(&src);
+}
+
+} // namespace geojson
+} // namespace android
+} // namespace mbgl