Fix #12920 FP functionConst for ref qualified member function (#6582)

Author: chrchr-github

lib/checkclass.cpp

@@ -2175,7 +2175,7 @@ void CheckClass::checkConst()
                 continue;
 
             const bool suggestStatic = memberAccessed != MemberAccess::MEMBER && !func.isOperator();
-            if ((returnsPtrOrRef || func.isConst()) && !suggestStatic)
+            if ((returnsPtrOrRef || func.isConst() || func.hasLvalRefQualifier()) && !suggestStatic)
                 continue;
 
             std::string classname = scope->className;

test/testclass.cpp

@@ -214,6 +214,7 @@ class TestClass : public TestFixture {
         TEST_CASE(const_shared_ptr);
         TEST_CASE(constPtrToConstPtr);
         TEST_CASE(constTrailingReturnType);
+        TEST_CASE(constRefQualified);
         TEST_CASE(staticArrayPtrOverload);
         TEST_CASE(qualifiedNameMember); // #10872
 
@@ -7496,6 +7497,16 @@ class TestClass : public TestFixture {
         ASSERT_EQUALS("", errout_str());
     }
 
+    void constRefQualified() { // #12920
+        checkConst("class Fred {\n"
+                   "public:\n"
+                   "    const Data& get() & { return data; }\n"
+                   "private:\n"
+                   "    Data data;\n"
+                   "};\n");
+        ASSERT_EQUALS("", errout_str());
+    }
+
     void staticArrayPtrOverload() {
         checkConst("struct S {\n"
                    "    template<size_t N>\n"