Fix #14425 FP functionStatic: function call on this with unknown base class (danmar#8151)

Co-authored-by: chrchr-github <noreply@github.com>

Author: chrchr-github

lib/checkclass.cpp

@@ -2353,6 +2353,8 @@ bool CheckClass::isMemberVar(const Scope *scope, const Token *tok) const
 bool CheckClass::isMemberFunc(const Scope *scope, const Token *tok)
 {
     if (!tok->function()) {
+        if (Token::simpleMatch(tok->astParent(), ".") && Token::simpleMatch(tok->astParent()->astOperand1(), "this"))
+            return true;
         for (const Function &func : scope->functionList) {
             if (func.name() == tok->str()) {
                 const Token* tok2 = tok->tokAt(2);

test/testclass.cpp

@@ -6827,6 +6827,11 @@ class TestClass : public TestFixture {
         ASSERT_EQUALS("[test.cpp:5:10]: (style) Either there is a missing 'override', or the member function 'S::g' can be static. [functionStatic]\n"
                       "[test.cpp:6:10]: (style) Either there is a missing 'override', or the member function 'S::h' can be static. [functionStatic]\n",
                       errout_str());
+
+        checkConst("struct S : U {\n" // #14425
+                   "    void f() { this->g(); }\n"
+                   "};\n");
+        ASSERT_EQUALS("", errout_str());
     }
 
     void const97() { // #13301