[core] Enable source volatile flag initalization in style

The source `volatile` flag value can be defined in the style as following:

```
"example_source": {
   "volatile": true
}
```

2 files changed, 16 insertions, 1 deletions

diff --git a/src/mbgl/style/conversion/source.cpp b/src/mbgl/style/conversion/source.cpp
index 14e020594a..80c8b893f7 100644
--- a/src/mbgl/style/conversion/source.cpp
+++ b/src/mbgl/style/conversion/source.cpp
@@ -9,6 +9,18 @@ namespace mbgl {
 namespace style {
 namespace conversion {
 
+namespace {
+bool setObjectMember(std::unique_ptr<Source>& source, const Convertible& value, const char* member, Error& error) {
+    if (auto memberValue = objectMember(value, member)) {
+        if (auto error_ = source->setProperty(member, *memberValue)) {
+            error = *error_;
+            return false;
+        }
+    }
+    return true;
+}
+} // namespace
+
 optional<std::unique_ptr<Source>> Converter<std::unique_ptr<Source>>::operator()(const Convertible& value,
                                                                                  Error& error,
                                                                                  const std::string& id) const {
@@ -32,6 +44,7 @@ optional<std::unique_ptr<Source>> Converter<std::unique_ptr<Source>>::operator()
 
     auto source = SourceManager::get()->createSource(tname, id, value, error);
     if (!source) return nullopt;
+    if (!setObjectMember(source, value, "volatile", error)) return nullopt;
     return source;
 }
 
diff --git a/test/map/map.test.cpp b/test/map/map.test.cpp
index 0370f51707..1d266b72e2 100644
--- a/test/map/map.test.cpp
+++ b/test/map/map.test.cpp
@@ -1059,7 +1059,8 @@ TEST(Map, UniversalStyleGetter) {
             },
             "mapbox-streets": {
                 "type": "vector",
-                "url": "http://api.example.com/tilejson.json"
+                "url": "http://api.example.com/tilejson.json",
+                "volatile": true
             },
             "image": {
                 "type": "image",
@@ -1120,6 +1121,7 @@ TEST(Map, UniversalStyleGetter) {
     ASSERT_TRUE(streetsSource);
     checkConstProperty(streetsSource, "url", "http://api.example.com/tilejson.json");
     checkConstProperty(streetsSource, "tiles", NullValue());
+    checkConstProperty(streetsSource, "volatile", true);
     // Image source properties
     Source* imageSource = test.map.getStyle().getSource("image");
     ASSERT_TRUE(imageSource);