[Clang] fixed false positive redeclaration error for using enum in nested scopes (#147711)

Fixes #147495 

--- 

This patch addresses the issue of false-positive redeclaration errors
that occur for `using enum` declarations in nested class scopes

```cpp
struct S {
  enum class E { A };
  using enum E;

  struct S1 {
    using enum E; // no error
  };
};
```

Author: a-tarasyuk

clang/docs/ReleaseNotes.rst

@@ -776,8 +776,10 @@ Bug Fixes in This Version
 - In C23, something like ``[[/*possible attributes*/]];`` is an attribute
   declaration, not a statement. So it is not allowed by the syntax in places
   where a statement is required, specifically as the secondary block of a
-  selection or iteration statement. This differs from C++, since C++ allows 
+  selection or iteration statement. This differs from C++, since C++ allows
   declaration statements. Clang now emits a warning for these patterns. (#GH141659)
+- Fixed false positives for redeclaration errors of using enum in
+  nested scopes. (#GH147495)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaDeclCXX.cpp

@@ -13308,7 +13308,7 @@ NamedDecl *Sema::BuildUsingEnumDeclaration(Scope *S, AccessSpecifier AS,
     LookupResult Previous(*this, UsingEnumName, LookupUsingDeclName,
                           RedeclarationKind::ForVisibleRedeclaration);
 
-    LookupName(Previous, S);
+    LookupQualifiedName(Previous, CurContext);
 
     for (NamedDecl *D : Previous)
       if (UsingEnumDecl *UED = dyn_cast<UsingEnumDecl>(D))

clang/test/SemaCXX/cxx20-using-enum.cpp

@@ -274,4 +274,18 @@ void f(int a) {
 }
 }
 
+namespace GH147495 {
+struct S {
+  enum class E { A };
+  using enum E;
+
+  struct S1 {
+    using enum E;
+  };
+
+  struct S2 {
+    using E::A;
+  };
+};
+}
 #endif