From 9cb8254600694de327fd73ae02dac216c9e81c64 Mon Sep 17 00:00:00 2001
From: naveen-seth <naveen.hanig@outlook.com>
Date: Tue, 4 Nov 2025 00:58:22 +0100
Subject: [PATCH] [clang][modules] Fix crash in enum visibility lookup for
 C++20 header units

Fixes #165445.

Fixes a crash when ASTWriter::GenerateNameLookupTable processes enum
constants from C++20 header units.

The special handling for enum constants, introduced in fccc6ee,
doesn't account for declarations whose owning module is a C++20 header
unit. It calls isNamedModule() on the result of
getTopLevelOwningNamedModule(), which returns null for header units,
causing a null pointer dereference.
---
 clang/lib/Serialization/ASTWriter.cpp         |  3 +-
 ...rash-enum-visibility-with-header-unit.cppm | 46 +++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Modules/crash-enum-visibility-with-header-unit.cppm

diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 3ac338e013deb..b1fd151790d96 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -4374,8 +4374,7 @@ class ASTDeclContextNameLookupTrait
     // parent of parent. We DON'T remove the enum constant from its parent. So
     // we don't need to care about merging problems here.
     if (auto *ECD = dyn_cast<EnumConstantDecl>(D);
-        ECD && DC.isFileContext() && ECD->getOwningModule() &&
-        ECD->getTopLevelOwningNamedModule()->isNamedModule()) {
+        ECD && DC.isFileContext() && ECD->getTopLevelOwningNamedModule()) {
       if (llvm::all_of(
               DC.noload_lookup(
                   cast<EnumDecl>(ECD->getDeclContext())->getDeclName()),
diff --git a/clang/test/Modules/crash-enum-visibility-with-header-unit.cppm b/clang/test/Modules/crash-enum-visibility-with-header-unit.cppm
new file mode 100644
index 0000000000000..90c57796dcf7e
--- /dev/null
+++ b/clang/test/Modules/crash-enum-visibility-with-header-unit.cppm
@@ -0,0 +1,46 @@
+// Fixes #165445
+
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 -x c++-user-header %t/header.h \
+// RUN:   -emit-header-unit -o %t/header.pcm
+//
+// RUN: %clang_cc1 -std=c++20 %t/A.cppm -fmodule-file=%t/header.pcm \
+// RUN:   -emit-module-interface -o %t/A.pcm
+// 
+// RUN: %clang_cc1 -std=c++20 %t/B.cppm -fmodule-file=%t/header.pcm \
+// RUN:   -emit-module-interface -o %t/B.pcm
+//
+// RUN: %clang_cc1 -std=c++20 %t/use.cpp \
+// RUN:   -fmodule-file=A=%t/A.pcm -fmodule-file=B=%t/B.pcm  \
+// RUN:   -fmodule-file=%t/header.pcm \
+// RUN:   -verify -fsyntax-only
+
+//--- enum.h
+enum E { Value };
+
+//--- header.h
+#include "enum.h"
+
+//--- A.cppm
+module;
+#include "enum.h"
+export module A;
+
+auto e = Value;
+
+//--- B.cppm
+export module B;
+import "header.h";
+
+auto e = Value;
+
+//--- use.cpp
+// expected-no-diagnostics
+import A;
+import B;
+#include "enum.h"
+
+auto e = Value;