Fix #13056 FN returnByReference with member of member (#6734)

Author: chrchr-github

lib/checkclass.cpp

@@ -3326,7 +3326,10 @@ static const Variable* getSingleReturnVar(const Scope* scope) {
         return nullptr;
     if (!start->astOperand1() || start->str() != "return")
         return nullptr;
-    return start->astOperand1()->variable();
+    const Token* tok = start->astOperand1();
+    if (tok->str() == ".")
+        tok = tok->astOperand2();
+    return tok->variable();
 }
 
 void CheckClass::checkReturnByReference()

lib/token.h

@@ -795,7 +795,7 @@ class CPPCHECKLIB Token {
         setFlag(fIsTemplateArg, value);
     }
 
-    std::string getMacroName() const {
+    const std::string& getMacroName() const {
         return mImpl->mMacroName;
     }
     void setMacroName(std::string name) {

test/testclass.cpp

@@ -9066,6 +9066,23 @@ class TestClass : public TestFixture {
                                "    std::string foo() && { return s; }\n" // <- used for temporary objects
                                "};\n");
         ASSERT_EQUALS("", errout_str());
+
+        checkReturnByReference("struct S1 {\n" // #13056
+                               "    std::string str;\n"
+                               "    struct T { std::string strT; } mT;\n"
+                               "};\n"
+                               "struct S2 {\n"
+                               "    std::string get1() const {\n"
+                               "        return mS1->str;\n"
+                               "    }\n"
+                               "    std::string get2() const {\n"
+                               "        return mS1->mT.strT;\n"
+                               "    }\n"
+                               "    S1* mS1;\n"
+                               "};\n");
+        ASSERT_EQUALS("[test.cpp:6]: (performance) Function 'get1()' should return member 'str' by const reference.\n"
+                      "[test.cpp:9]: (performance) Function 'get2()' should return member 'strT' by const reference.\n",
+                      errout_str());
     }
 };