fix access checking about function overloading (#107768)

fix #107629

After some more debugging, I find out that we will check access here at
https://github.com/llvm/llvm-project/blob/8e010ac5a173c9dee44b44324169a3e100a1a6fc/clang/lib/Sema/SemaInit.cpp#L7807

And for `f()` inside code below, `Found.getAccess()` is `AS_none` hence
`CheckAddressOfMemberAccess` return `AR_accessible` directly.

```cpp
struct Base {
public:
  int f(int);
private:
  int f();  // expect-note {{declared private here}}
};

struct Derived : public Base {};

void f() {
  int(Derived::* public_f)(int) = &Derived::f;
  int(Derived::* private_f)() = &Derived::f;  // expect-error {{'f' is a private member of 'Base'}}
}
```

I think the `Found.getAccess()` is intended to be `AS_none` so I just
add one more access check for the `UnresolvedLookupExpr` when
`Found.getAccess()` is `AS_none`. If add the check unconditionally clang
will report lots of duplicate errors and cause several unit tests to
fail.

I also test the UB mentioned in
#107629 and clang now display
4 `false` as expecetd.

Co-authored-by: Erich Keane <[email protected]>

Author: Backl1ght

clang/docs/ReleaseNotes.rst

@@ -840,6 +840,7 @@ Bug Fixes to C++ Support
 - Fixed a pack substitution bug in deducing class template partial specializations. (#GH53609)
 - Fixed a crash when constant evaluating some explicit object member assignment operators. (#GH142835)
 - Fixed an access checking bug when substituting into concepts (#GH115838)
+- Fix a bug where private access specifier of overloaded function not respected. (#GH107629)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaOverload.cpp

@@ -16981,6 +16981,9 @@ ExprResult Sema::FixOverloadedFunctionReference(Expr *E, DeclAccessPair Found,
   }
 
   if (UnresolvedLookupExpr *ULE = dyn_cast<UnresolvedLookupExpr>(E)) {
+    if (Found.getAccess() == AS_none) {
+      CheckUnresolvedLookupAccess(ULE, Found);
+    }
     // FIXME: avoid copy.
     TemplateArgumentListInfo TemplateArgsBuffer, *TemplateArgs = nullptr;
     if (ULE->hasExplicitTemplateArgs()) {

clang/test/CXX/class.access/p4.cpp

@@ -21,11 +21,13 @@ namespace test0 {
   public:
     void foo(Public&);
   protected:
-    void foo(Protected&); // expected-note 2 {{declared protected here}}
+    void foo(Protected&); // expected-note 4 {{declared protected here}}
   private:
-    void foo(Private&); // expected-note 2 {{declared private here}}
+    void foo(Private&); // expected-note 4 {{declared private here}}
   };
 
+  class B : public A {};
+
   void test(A *op) {
     op->foo(PublicInst);
     op->foo(ProtectedInst); // expected-error {{'foo' is a protected member}}
@@ -35,6 +37,16 @@ namespace test0 {
     void (A::*b)(Protected&) = &A::foo; // expected-error {{'foo' is a protected member}}
     void (A::*c)(Private&) = &A::foo; // expected-error {{'foo' is a private member}}
   }
+
+  void test(B *op) {
+    op->foo(PublicInst);
+    op->foo(ProtectedInst); // expected-error {{'foo' is a protected member}}
+    op->foo(PrivateInst); // expected-error {{'foo' is a private member}}
+
+    void (B::*a)(Public&) = &B::foo;
+    void (B::*b)(Protected&) = &B::foo; // expected-error {{'foo' is a protected member}}
+    void (B::*c)(Private&) = &B::foo; // expected-error {{'foo' is a private member}}
+  }
 }
 
 // Member operators.