Fixed #6674 (false positive 'unusedPrivateFunction' - calling virtual function in subclass)

lib/symboldatabase.cpp

@@ -2789,7 +2789,9 @@ bool Function::isImplicitlyVirtual_rec(const ::Type* baseType, bool& safe) const
 
                     // check for matching return parameters
                     while (temp1->str() != "virtual") {
-                        if (temp1->str() != temp2->str()) {
+                        if (temp1->str() != temp2->str() &&
+                            !(temp1->str() == derivedFromType->name() &&
+                              temp2->str() == baseType->name())) {
                             returnMatch = false;
                             break;
                         }

test/testunusedprivfunc.cpp

@@ -481,6 +481,24 @@ private:
               "    void func() {}\n"
               "};");
         ASSERT_EQUALS("", errout.str());
+
+        check("class Base {\n"
+              "public:\n"
+              "    void dostuff() {\n"
+              "      f();\n"
+              "    }\n"
+              "\n"
+              "private:\n"
+              "    virtual Base* f() = 0;\n"
+              "};\n"
+              "\n"
+              "class Derived : public Base {\n"
+              "private:\n"
+              "    Derived* f() {\n"
+              "      return 0;\n"
+              "    }\n"
+              "};");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void friendClass() {