[core] Add style::Source::setVolatile()/isVolatile() API

include/mbgl/style/source.hpp

@@ -66,12 +66,14 @@ public:
     std::string getID() const;
     optional<std::string> getAttribution() const;
 
+    // The data from the volatile sources are not stored in a persistent storage.
+    bool isVolatile() const noexcept;
+    void setVolatile(bool) noexcept;
+
     // Private implementation
     class Impl;
     Immutable<Impl> baseImpl;
 
-    Source(Immutable<Impl>);
-
     void setObserver(SourceObserver*);
     SourceObserver* observer = nullptr;
 
@@ -114,6 +116,7 @@ public:
     virtual mapbox::base::WeakPtr<Source> makeWeakPtr() = 0;
 
 protected:
+    explicit Source(Immutable<Impl>);
     virtual Mutable<Impl> createMutable() const noexcept = 0;
 };
 

src/mbgl/style/source.cpp

@@ -27,6 +27,18 @@ optional<std::string> Source::getAttribution() const {
     return baseImpl->getAttribution();
 }
 
+bool Source::isVolatile() const noexcept {
+    return baseImpl->isVolatile();
+}
+
+void Source::setVolatile(bool set) noexcept {
+    if (isVolatile() == set) return;
+    auto newImpl = createMutable();
+    newImpl->setVolatile(set);
+    baseImpl = std::move(newImpl);
+    observer->onSourceChanged(*this);
+}
+
 void Source::setObserver(SourceObserver* observer_) {
     observer = observer_ ? observer_ : &nullObserver;
 }

src/mbgl/style/source_impl.hpp

@@ -1,7 +1,6 @@
 #pragma once
 
 #include <mbgl/style/source.hpp>
-#include <mbgl/util/noncopyable.hpp>
 
 #include <string>
 
@@ -27,6 +26,8 @@ public:
     void setMaxOverscaleFactorForParentTiles(optional<uint8_t> overscaleFactor) noexcept;
     optional<uint8_t> getMaxOverscaleFactorForParentTiles() const noexcept;
 
+    bool isVolatile() const { return volatileFlag; }
+    void setVolatile(bool set) { volatileFlag = set; }
     const SourceType type;
     const std::string id;
 
@@ -34,6 +35,7 @@ protected:
     optional<uint8_t> prefetchZoomDelta;
     optional<uint8_t> maxOverscaleFactor;
     Duration minimumTileUpdateInterval{Duration::zero()};
+    bool volatileFlag = false;
 
     Impl(SourceType, std::string);
     Impl(const Impl&) = default;