Vk: variadic Is[Instance]Extension checks.

Because I'd like to static_assert on these.

src/Magnum/Vk/Test/ExtensionsTest.cpp

@@ -62,6 +62,25 @@ void ExtensionsTest::isInstanceExtension() {
     CORRADE_VERIFY(Implementation::IsInstanceExtension<Extensions::KHR::get_physical_device_properties2>::value);
     CORRADE_VERIFY(!Implementation::IsInstanceExtension<Extensions::KHR::external_memory>::value);
     CORRADE_VERIFY(!Implementation::IsInstanceExtension<int>::value);
+
+    /* Variadic check (used in variadic addEnabledExtensions()), check that it
+       properly fails for each occurence of a device extension */
+    CORRADE_VERIFY((Implementation::IsInstanceExtension<
+        Extensions::KHR::get_physical_device_properties2,
+        Extensions::KHR::external_memory_capabilities,
+        Extensions::KHR::external_fence_capabilities>::value));
+    CORRADE_VERIFY(!(Implementation::IsInstanceExtension<
+        Extensions::KHR::draw_indirect_count, /* not */
+        Extensions::KHR::external_memory_capabilities,
+        Extensions::KHR::external_fence_capabilities>::value));
+    CORRADE_VERIFY(!(Implementation::IsInstanceExtension<
+        Extensions::KHR::get_physical_device_properties2,
+        Extensions::KHR::external_memory, /* not */
+        Extensions::KHR::external_fence_capabilities>::value));
+    CORRADE_VERIFY(!(Implementation::IsInstanceExtension<
+        Extensions::KHR::get_physical_device_properties2,
+        Extensions::KHR::external_memory_capabilities,
+        Extensions::KHR::external_fence>::value)); /* not */
 }
 
 void ExtensionsTest::isExtension() {
@@ -79,6 +98,25 @@ void ExtensionsTest::isExtension() {
         CORRADE_EXPECT_FAIL("GL/AL extensions are not rejected right now.");
         CORRADE_VERIFY(!Implementation::IsExtension<GLExtension>::value);
     }
+
+    /* Variadic check (used in variadic addEnabledExtensions()), check that it
+       properly fails for each occurence of a device extension */
+    CORRADE_VERIFY((Implementation::IsExtension<
+        Extensions::KHR::external_memory,
+        Extensions::KHR::depth_stencil_resolve,
+        Extensions::KHR::external_fence>::value));
+    CORRADE_VERIFY(!(Implementation::IsExtension<
+        Extensions::KHR::external_memory_capabilities, /* not */
+        Extensions::KHR::depth_stencil_resolve,
+        Extensions::KHR::external_fence>::value));
+    CORRADE_VERIFY(!(Implementation::IsExtension<
+        Extensions::KHR::external_memory,
+        Extensions::EXT::debug_report, /* not */
+        Extensions::KHR::external_fence>::value));
+    CORRADE_VERIFY(!(Implementation::IsExtension<
+        Extensions::KHR::external_memory,
+        Extensions::KHR::depth_stencil_resolve,
+        Extensions::KHR::external_fence_capabilities>::value)); /* not */
 }
 
 void ExtensionsTest::constructInstanceExtensionFromCompileTimeExtension() {

src/Magnum/Vk/TypeTraits.h

@@ -38,8 +38,20 @@ namespace Implementation {
     /* Put into a separate header so APIs that need it don't need to pull in
        the whole Extensions.h. Tested in ExtensionsTest also. */
     /** @todo filter out GL/AL extensions also */
-    CORRADE_HAS_TYPE(IsInstanceExtension, decltype(T::InstanceIndex));
-    CORRADE_HAS_TYPE(IsExtension, decltype(T::Index));
+
+    template<class...> class IsInstanceExtension;
+    CORRADE_HAS_TYPE(IsInstanceExtension<U>, decltype(T::InstanceIndex));
+    template<class T, class U, class ...Args> class IsInstanceExtension<T, U, Args...> {
+        /** @todo C++17: use &&... instead of all this */
+        public: enum: bool { value = IsInstanceExtension<T>::value && IsInstanceExtension<U, Args...>::value };
+    };
+
+    template<class...> class IsExtension;
+    CORRADE_HAS_TYPE(IsExtension<U>, decltype(T::Index));
+    template<class T, class U, class ...Args> class IsExtension<T, U, Args...> {
+        /** @todo C++17: use &&... instead of all this */
+        public: enum: bool { value = IsExtension<T>::value && IsExtension<U, Args...>::value };
+    };
 }
 
 }}