Declare mbgl::style::GeoJSONOptions as immutable

platform/darwin/src/MGLShapeSource.mm

@@ -27,7 +27,7 @@
 const MGLShapeSourceOption MGLShapeSourceOptionSimplificationTolerance = @"MGLShapeSourceOptionSimplificationTolerance";
 const MGLShapeSourceOption MGLShapeSourceOptionLineDistanceMetrics = @"MGLShapeSourceOptionLineDistanceMetrics";
 
-mbgl::style::GeoJSONOptions MGLGeoJSONOptionsFromDictionary(NSDictionary<MGLShapeSourceOption, id> *options) {
+mbgl::Immutable<mbgl::style::GeoJSONOptions> MGLGeoJSONOptionsFromDictionary(NSDictionary<MGLShapeSourceOption, id> *options) {
     auto geoJSONOptions = mbgl::style::GeoJSONOptions();
 
     if (NSNumber *value = options[MGLShapeSourceOptionMinimumZoomLevel]) {
@@ -145,7 +145,7 @@
         geoJSONOptions.lineMetrics = value.boolValue;
     }
 
-    return geoJSONOptions;
+    return mbgl::makeMutable<mbgl::style::GeoJSONOptions>(std::move(geoJSONOptions));
 }
 
 @interface MGLShapeSource ()

platform/darwin/src/MGLShapeSource_Private.h

@@ -1,5 +1,6 @@
 #import "MGLFoundation.h"
 #import "MGLShapeSource.h"
+#include <mbgl/util/immutable.hpp>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -10,7 +11,7 @@ namespace mbgl {
 }
 
 MGL_EXPORT
-mbgl::style::GeoJSONOptions MGLGeoJSONOptionsFromDictionary(NSDictionary<MGLShapeSourceOption, id> *options);
+mbgl::Immutable<mbgl::style::GeoJSONOptions> MGLGeoJSONOptionsFromDictionary(NSDictionary<MGLShapeSourceOption, id> *options);
 
 @interface MGLShapeSource (Private)