[core] guard against duplicate source id’s

src/mbgl/style/style.cpp

@@ -136,6 +136,16 @@ void Style::setJSON(const std::string& json) {
 }
 
 void Style::addSource(std::unique_ptr<Source> source) {
+    //Guard against duplicate source ids
+    auto it = std::find_if(sources.begin(), sources.end(), [&](const auto& existing) {
+        return existing->getID() == source->getID();
+    });
+
+    if (it != sources.end()) {
+        std::string msg = "Source " + source->getID() + " already exists";
+        throw std::runtime_error(msg.c_str());
+    }
+
     source->baseImpl->setObserver(this);
     sources.emplace_back(std::move(source));
 }

test/style/style.test.cpp

@@ -3,10 +3,13 @@
 
 #include <mbgl/style/style.hpp>
 #include <mbgl/style/source_impl.hpp>
+#include <mbgl/style/sources/vector_source.hpp>
 #include <mbgl/style/layer.hpp>
 #include <mbgl/util/io.hpp>
 #include <mbgl/util/run_loop.hpp>
 
+#include <memory>
+
 using namespace mbgl;
 using namespace mbgl::style;
 
@@ -113,3 +116,21 @@ TEST(Style, Properties) {
     ASSERT_EQ(0, style.getDefaultZoom());
     ASSERT_EQ(0, style.getDefaultPitch());
 }
+
+TEST(Style, DuplicateSource) {
+    util::RunLoop loop;
+
+    StubFileSource fileSource;
+    Style style { fileSource, 1.0 };
+
+    style.setJSON(util::read_file("test/fixtures/resources/style-unused-sources.json"));
+
+    style.addSource(std::make_unique<VectorSource>("sourceId", "mapbox://mapbox.mapbox-terrain-v2"));
+
+    try {
+        style.addSource(std::make_unique<VectorSource>("sourceId", "mapbox://mapbox.mapbox-terrain-v2"));
+        FAIL() << "Should not have been allowed to add a duplicate source id";
+    } catch (std::runtime_error) {
+        //Expected
+    }
+}