Accept nullptr in AbstractResourceLoader::set().

Also implement setNotFound() using set() and make the code more
flexible.

doc/changelog.dox

@@ -139,6 +139,9 @@ See also:
 
 -   The @ref ResourceManager class now accepts also
     @ref Corrade::Containers::Pointer instances in addition to raw pointers
+-   The @ref AbstractResourceLoader::set() function now accepts also
+    @cpp nullptr @ce for explicitly setting @ref ResourceDataState::Loading or
+    @ref ResourceDataState::NotFound resources
 
 @subsubsection changelog-latest-changes-animation Animation library
 

src/Magnum/AbstractResourceLoader.h

@@ -130,10 +130,17 @@ template<class T> class AbstractResourceLoader {
         /**
          * @brief Set loaded resource to resource manager
          *
-         * Also increments count of loaded resources. Parameter @p state must
-         * be either @ref ResourceDataState::Mutable or
-         * @ref ResourceDataState::Final. See @ref ResourceManager::set() for
+         * If @p data is @cpp nullptr @ce and @p state is
+         * @ref ResourceDataState::NotFound, increments count of not found
+         * resources. Otherwise, if @p data is not @cpp nullptr @ce, increments
+         * count of loaded resources. See @ref ResourceManager::set() for
          * more information.
+         *
+         * Note that resource's state is automatically set to
+         * @ref ResourceDataState::Loading when it is requested from
+         * @ref ResourceManager and it's not loaded yet, so it's not needed to
+         * call this function. For marking a resource as not found you can also
+         * use the convenience @ref setNotFound() variant.
          * @see @ref loadedCount()
          */
         void set(ResourceKey key, T* data, ResourceDataState state, ResourcePolicy policy);
@@ -144,7 +151,7 @@ template<class T> class AbstractResourceLoader {
         }
 
         /** @overload */
-        template<class U> void set(ResourceKey key, U&& data, ResourceDataState state, ResourcePolicy policy) {
+        template<class U, class = typename std::enable_if<!std::is_same<typename std::decay<U>::type, std::nullptr_t>::value>::type> void set(ResourceKey key, U&& data, ResourceDataState state, ResourcePolicy policy) {
             set(key, new typename std::decay<U>::type(std::forward<U>(data)), state, policy);
         }
 
@@ -164,18 +171,21 @@ template<class T> class AbstractResourceLoader {
         }
 
         /** @overload */
-        template<class U> void set(ResourceKey key, U&& data) {
+        template<class U, class = typename std::enable_if<!std::is_same<typename std::decay<U>::type, std::nullptr_t>::value>::type> void set(ResourceKey key, U&& data) {
             set(key, new typename std::decay<U>::type(std::forward<U>(data)));
         }
 
         /**
          * @brief Mark resource as not found
          *
-         * Also increments count of not found resources. See also
-         * @ref ResourceManager::set() for more information.
+         * A convenience function calling @ref set() with @cpp nullptr @ce
+         * and @ref ResourceDataState::NotFound.
          * @see @ref notFoundCount()
          */
-        void setNotFound(ResourceKey key);
+        void setNotFound(ResourceKey key) {
+            /** @todo What policy for notfound resources? */
+            set(key, nullptr, ResourceDataState::NotFound, ResourcePolicy::Resident);
+        }
 
     #ifndef DOXYGEN_GENERATING_OUTPUT
     private:
@@ -222,18 +232,11 @@ template<class T> void AbstractResourceLoader<T>::load(ResourceKey key) {
 }
 
 template<class T> void AbstractResourceLoader<T>::set(ResourceKey key, T* data, ResourceDataState state, ResourcePolicy policy) {
-    CORRADE_ASSERT(state == ResourceDataState::Mutable || state == ResourceDataState::Final,
-        "AbstractResourceLoader::set(): state must be either Mutable or Final", );
-    ++_loadedCount;
+    if(data) ++_loadedCount;
+    if(!data && state == ResourceDataState::NotFound) ++_notFoundCount;
     manager->set(key, data, state, policy);
 }
 
-template<class T> inline void AbstractResourceLoader<T>::setNotFound(ResourceKey key) {
-    ++_notFoundCount;
-    /** @todo What policy for notfound resources? */
-    manager->set(key, nullptr, ResourceDataState::NotFound, ResourcePolicy::Resident);
-}
-
 }
 
 #endif

src/Magnum/Test/ResourceManagerTest.cpp

@@ -44,7 +44,9 @@ struct ResourceManagerTest: TestSuite::Tester {
     void defaults();
     void clear();
     void clearWhileReferenced();
+
     void loader();
+    void loaderSetNullptr();
 
     void debugResourceState();
 };
@@ -71,7 +73,9 @@ ResourceManagerTest::ResourceManagerTest() {
               &ResourceManagerTest::defaults,
               &ResourceManagerTest::clear,
               &ResourceManagerTest::clearWhileReferenced,
+
               &ResourceManagerTest::loader,
+              &ResourceManagerTest::loaderSetNullptr,
 
               &ResourceManagerTest::debugResourceState});
 }
@@ -333,6 +337,52 @@ void ResourceManagerTest::loader() {
     CORRADE_COMPARE(Data::count, 0);
 }
 
+void ResourceManagerTest::loaderSetNullptr() {
+    class IntResourceLoader: public AbstractResourceLoader<Int> {
+        public:
+            void load() {
+                set("hello", 1337, ResourceDataState::Final, ResourcePolicy::Resident);
+                set("world", 42, ResourceDataState::Final, ResourcePolicy::Resident);
+            }
+
+        private:
+            void doLoad(ResourceKey key) override {
+                /* Verify that calling load() with nullptr + Loading works */
+                set(key, nullptr, ResourceDataState::Loading, ResourcePolicy::Resident);
+                set("world", nullptr, ResourceDataState::Loading, ResourcePolicy::Resident);
+            }
+    };
+
+    ResourceManager rm;
+    Containers::Pointer<IntResourceLoader> loaderPtr{Containers::InPlaceInit};
+    IntResourceLoader& loader = *loaderPtr;
+    rm.setLoader<Int>(std::move(loaderPtr));
+
+    CORRADE_COMPARE(rm.state<Int>("hello"), ResourceState::NotLoaded);
+    CORRADE_COMPARE(rm.state<Int>("world"), ResourceState::NotLoaded);
+
+    /* Loading "hello" triggers a load of "world" as well */
+    Resource<Int> hello = rm.get<Int>("hello");
+    CORRADE_COMPARE(hello.state(), ResourceState::Loading);
+    CORRADE_COMPARE(rm.state<Int>("world"), ResourceState::Loading);
+    CORRADE_COMPARE(loader.requestedCount(), 1);
+    CORRADE_COMPARE(loader.loadedCount(), 0);
+    CORRADE_COMPARE(loader.notFoundCount(), 0);
+
+    /* Load the things */
+    loader.load();
+    CORRADE_COMPARE(hello.state(), ResourceState::Final);
+    CORRADE_COMPARE(*hello, 1337);
+    CORRADE_COMPARE(loader.requestedCount(), 1);
+    CORRADE_COMPARE(loader.loadedCount(), 2);
+    CORRADE_COMPARE(loader.notFoundCount(), 0);
+
+    /* World is now loaded as well as a side-effect */
+    Resource<Int> world = rm.get<Int>("world");
+    CORRADE_COMPARE(world.state(), ResourceState::Final);
+    CORRADE_COMPARE(*world, 42);
+}
+
 void ResourceManagerTest::debugResourceState() {
     std::ostringstream out;
     Debug{&out} << ResourceState::Loading << ResourceState(0xbe);