Fix #12626 FP returnByReference with string_view or template (#6311)

Author: chrchr-github

lib/checkclass.cpp

@@ -3330,6 +3330,11 @@ void CheckClass::checkReturnByReference()
                 continue;
             if (func.isImplicitlyVirtual())
                 continue;
+            if (func.isOperator())
+                continue;
+            if (const Library::Container* container = mSettings->library.detectContainer(func.retDef))
+                if (container->view)
+                    continue;
             if (const Variable* var = getSingleReturnVar(func.functionScope)) {
                 if (!var->valueType())
                     continue;

test/testclass.cpp

@@ -8964,6 +8964,19 @@ class TestClass : public TestFixture {
         checkReturnByReference("struct S { S(); };\n" // #12620
                                "S::S() = delete;\n");
         ASSERT_EQUALS("", errout_str()); // don't crash
+
+        checkReturnByReference("struct S {\n" // #12626
+                               "    std::string s;\n"
+                               "    operator std::string_view() const { return s; }\n"
+                               "    std::string_view get() const { return s; }\n"
+                               "};\n"
+                               "template<typename T>\n"
+                               "struct U {\n"
+                               "    T t;\n"
+                               "    operator const T& () const { return t; }\n"
+                               "};\n"
+                               "U<std::string> u;\n");
+        ASSERT_EQUALS("", errout_str());
     }
 };