[Clang] Correctly diagnose a static function overloading a non-static function (#93460)

Regression in clang 18 introduced by af47517

Fixes #93456

Author: cor3ntin

clang/docs/ReleaseNotes.rst

@@ -797,6 +797,8 @@ Bug Fixes to C++ Support
   in dependent contexts. Fixes (#GH92680).
 - Fixed a crash when diagnosing failed conversions involving template parameter
   packs. (#GH93076)
+- Fixed a regression introduced in Clang 18 causing a static function overloading a non-static function
+  with the same parameters not to be diagnosed. (Fixes #GH93456).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaOverload.cpp

@@ -1482,7 +1482,7 @@ static bool IsOverloadOrOverrideImpl(Sema &SemaRef, FunctionDecl *New,
   }
 
   if (OldMethod && NewMethod && !OldMethod->isStatic() &&
-      !OldMethod->isStatic()) {
+      !NewMethod->isStatic()) {
     bool HaveCorrespondingObjectParameters = [&](const CXXMethodDecl *Old,
                                                  const CXXMethodDecl *New) {
       auto NewObjectType = New->getFunctionObjectParameterReferenceType();

clang/test/SemaCXX/overload-decl.cpp

@@ -36,3 +36,20 @@ class X {
 
 int main() {} // expected-note {{previous definition is here}}
 int main(int,char**) {} // expected-error {{conflicting types for 'main'}}
+
+
+namespace GH93456 {
+
+struct X {
+  static void f(); // expected-note {{previous declaration is here}}
+  void f() const;
+  // expected-error@-1 {{static and non-static member functions with the same parameter types cannot be overloaded}}
+};
+
+struct Y {
+  void f() const; // expected-note {{previous declaration is here}}
+  static void f();
+  // expected-error@-1 {{static and non-static member functions with the same parameter types cannot be overloaded}}
+};
+
+}