Resolving issue #119101

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -449,6 +449,8 @@ def err_typename_invalid_constexpr : Error<
   "to be specified">;
 def err_typename_identifiers_only : Error<
   "typename is allowed for identifiers only">;
+def err_storage_class_before_class_decl : Error<
+  "'%0' is not allowed before a class declaration">;
 
 def err_friend_invalid_in_context : Error<
   "'friend' used outside of class">;

clang/lib/Parse/Parser.cpp

@@ -1254,6 +1254,18 @@ Parser::DeclGroupPtrTy Parser::ParseDeclarationOrFunctionDefinition(
         Actions.getASTContext().getSourceManager());
   });
 
+  if (DS->getStorageClassSpec() != DeclSpec::SCS_unspecified) {
+  // Check if the next token starts a class/struct/union/enum declaration
+    if (Tok.isOneOf(tok::kw_class, tok::kw_struct, tok::kw_union, tok::kw_enum)) {
+      // Emit an error: storage class specifiers are not allowed before class declarations
+      Diag(DS->getStorageClassSpecLoc(), diag::err_storage_class_before_class_decl)
+          << DeclSpec::getSpecifierName(DS->getStorageClassSpec());
+
+      // Optionally, consume the storage class specifier to continue parsing
+      DS->ClearStorageClassSpecs();
+    }
+  }
+
   if (DS) {
     return ParseDeclOrFunctionDefInternal(Attrs, DeclSpecAttrs, *DS, AS);
   } else {

clang/test/SemaCXX/invalid-storage-class.cpp

@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+auto class X1 {}; // expected-error {{'auto' is not allowed before a class declaration}}
+
+static struct X2 {}; // expected-error {{'static' is not allowed before a class declaration}}
+
+register union X3 {}; // expected-error {{'register' is not allowed before a class declaration}}