Fixed #14127 (false positive: unusedPrivateFunction with [[maybe_unused]] attribute) (cppcheck-opensource#7917)

Author: danmar

lib/checkclass.cpp

@@ -1346,6 +1346,10 @@ void CheckClass::privateFunctions()
                 privateFuncs.pop_front();
                 continue;
             }
+            if (pf->tokenDef && pf->tokenDef->isAttributeMaybeUnused()) {
+                privateFuncs.pop_front();
+                continue;
+            }
             // Check that all private functions are used
             bool used = checkFunctionUsage(pf, scope); // Usage in this class
             // Check in friend classes

test/testunusedprivfunc.cpp

@@ -882,6 +882,12 @@ class TestUnusedPrivateFunction : public TestFixture {
               "    [[maybe_unused]] int f() { return 42; }\n"
               "};");
         ASSERT_EQUALS("", errout_str());
+
+        check("class C {\n"
+              "    [[maybe_unused]] static int f();\n"
+              "};\n"
+              "int C::f() { return 42; }\n");
+        ASSERT_EQUALS("", errout_str());
     }
 
     void trailingReturn() {