From df9769e14b79048331c33deeda1a93acc9a4a73e Mon Sep 17 00:00:00 2001
From: "Oleksandr T." <oleksandr.tarasiuk@outlook.com>
Date: Fri, 1 Nov 2024 07:13:33 +0200
Subject: [PATCH] [Clang] prevent setting default lexical access specifier for
 missing primary declarations (#112424)

This PR resolves a crash triggered by a forward reference to an enum
type in a function parameter list. The fix includes setting `Invalid`
when `TagUseKind` is `Declaration` to ensure correct error handling.

Fixes #112208
---
 clang/docs/ReleaseNotes.rst | 1 +
 clang/lib/Sema/SemaDecl.cpp | 2 ++
 clang/test/SemaCXX/enum.cpp | 8 ++++++++
 3 files changed, 11 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 4e542ee91a8b..b99dd441db25 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -589,6 +589,7 @@ Bug Fixes to C++ Support
 - Fixed an assertion failure in range calculations for conditional throw expressions. (#GH111854)
 - Clang now correctly ignores previous partial specializations of member templates explicitly specialized for
   an implicitly instantiated class template specialization. (#GH51051)
+- Fixed an assertion failure caused by invalid enum forward declarations. (#GH112208)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index c56883a80c1c..0cdace25aa79 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -17955,6 +17955,8 @@ CreateNewDecl:
             << Name;
         Invalid = true;
       }
+      if (TUK == TagUseKind::Declaration)
+        Invalid = true;
     } else if (!PrevDecl) {
       Diag(Loc, diag::warn_decl_in_param_list) << Context.getTagDeclType(New);
     }
diff --git a/clang/test/SemaCXX/enum.cpp b/clang/test/SemaCXX/enum.cpp
index 9c398cc8da88..44042d8bf5cf 100644
--- a/clang/test/SemaCXX/enum.cpp
+++ b/clang/test/SemaCXX/enum.cpp
@@ -143,3 +143,11 @@ struct PR28903 {
     })
   };
 };
+
+namespace GH112208 {
+class C {
+  enum E { e = 0 };
+  void f(int, enum E;); // expected-error {{ISO C++ forbids forward references to 'enum' types}} \
+                        // expected-error {{unexpected ';' before ')'}}
+};
+}