fix: Fix a bug in isAutoCreationClass<T>. (#2277)

Author: tanglong3bf

lib/inc/drogon/DrObject.h

@@ -61,9 +61,9 @@ template <typename T>
 struct isAutoCreationClass
 {
     template <class C>
-    static constexpr auto check(C *)
-        -> std::enable_if_t<std::is_same_v<decltype(C::isAutoCreation), bool>,
-                            bool>
+    static constexpr auto check(C *) -> std::enable_if_t<
+        std::is_same_v<decltype(C::isAutoCreation), const bool>,
+        bool>
     {
         return C::isAutoCreation;
     }

lib/tests/unittests/DrObjectTest.cc

@@ -1,5 +1,6 @@
 #include <drogon/DrObject.h>
 #include <drogon/drogon_test.h>
+#include <drogon/HttpController.h>
 
 using namespace drogon;
 
@@ -41,3 +42,45 @@ DROGON_TEST(DrObjectNamespaceTest)
     CHECK(objPtr2.get() != nullptr);
     CHECK(objPtr == objPtr2);
 }
+
+class TestC : public DrObject<TestC>
+{
+  public:
+    static constexpr bool isAutoCreation = true;
+};
+
+class TestD : public DrObject<TestD>
+{
+  public:
+    static constexpr bool isAutoCreation = false;
+};
+
+class TestE : public DrObject<TestE>
+{
+  public:
+    static constexpr double isAutoCreation = 3.0;
+};
+
+class CtrlA : public HttpController<CtrlA>
+{
+  public:
+    METHOD_LIST_BEGIN
+    METHOD_LIST_END
+};
+
+class CtrlB : public HttpController<CtrlB, false>
+{
+  public:
+    METHOD_LIST_BEGIN
+    METHOD_LIST_END
+};
+
+DROGON_TEST(IsAutoCreationClassTest)
+{
+    STATIC_REQUIRE(isAutoCreationClass<TestA>::value == false);
+    STATIC_REQUIRE(isAutoCreationClass<TestC>::value == true);
+    STATIC_REQUIRE(isAutoCreationClass<TestD>::value == false);
+    STATIC_REQUIRE(isAutoCreationClass<TestE>::value == false);
+    STATIC_REQUIRE(isAutoCreationClass<CtrlA>::value == true);
+    STATIC_REQUIRE(isAutoCreationClass<CtrlB>::value == false);
+}