From 782f26e726eca801f52414d8ae7a546bc3668013 Mon Sep 17 00:00:00 2001
From: Egor Zhdan <e_zhdan@apple.com>
Date: Mon, 23 Jun 2025 16:25:48 +0100
Subject: [PATCH] [cxx-interop] Fix printing of namespaces declared in bridging
 headers

If a C++ namespace has redeclarations in a bridging header, printing AST for the namespace would crash the compiler. This is because such a redeclaration would not have an owning Clang module, and the AST printer did not account for that.

This change fixes the crash.

rdar://151715540
(cherry picked from commit cc9c51deea8698fdc1be90ffbfd7ca525b6ad33d)
---
 lib/AST/ASTPrinter.cpp                            |  4 ++++
 .../Cxx/namespace/Inputs/bridging-header.h        | 15 +++++++++++++++
 .../bridging-header-module-interface.swift        |  4 ++++
 3 files changed, 23 insertions(+)
 create mode 100644 test/Interop/Cxx/namespace/Inputs/bridging-header.h
 create mode 100644 test/Interop/Cxx/namespace/bridging-header-module-interface.swift

diff --git a/lib/AST/ASTPrinter.cpp b/lib/AST/ASTPrinter.cpp
index 453f54fa38f19..e6cf506e37d51 100644
--- a/lib/AST/ASTPrinter.cpp
+++ b/lib/AST/ASTPrinter.cpp
@@ -2737,6 +2737,10 @@ static void addNamespaceMembers(Decl *decl,
     declOwner = declOwner->getTopLevelModule();
   auto Redecls = llvm::SmallVector<clang::NamespaceDecl *, 2>(namespaceDecl->redecls());
   std::stable_sort(Redecls.begin(), Redecls.end(), [&](clang::NamespaceDecl *LHS, clang::NamespaceDecl *RHS) {
+    // A namespace redeclaration will not have an owning Clang module if it is
+    // declared in a bridging header.
+    if (!LHS->getOwningModule() || !RHS->getOwningModule())
+      return (bool)LHS->getOwningModule() < (bool)RHS->getOwningModule();
     return LHS->getOwningModule()->Name < RHS->getOwningModule()->Name;
   });
   for (auto redecl : Redecls) {
diff --git a/test/Interop/Cxx/namespace/Inputs/bridging-header.h b/test/Interop/Cxx/namespace/Inputs/bridging-header.h
new file mode 100644
index 0000000000000..1cc267d42c360
--- /dev/null
+++ b/test/Interop/Cxx/namespace/Inputs/bridging-header.h
@@ -0,0 +1,15 @@
+namespace NS1 {
+namespace NS2 {
+
+struct InBridgingHeader1 {};
+
+} // namespace NS2
+} // namespace NS1
+
+namespace NS1 {
+namespace NS2 {
+
+struct InBridgingHeader2 {};
+
+} // namespace NS2
+} // namespace NS1
diff --git a/test/Interop/Cxx/namespace/bridging-header-module-interface.swift b/test/Interop/Cxx/namespace/bridging-header-module-interface.swift
new file mode 100644
index 0000000000000..f068c5da6e3f1
--- /dev/null
+++ b/test/Interop/Cxx/namespace/bridging-header-module-interface.swift
@@ -0,0 +1,4 @@
+// RUN: %target-swift-ide-test -print-header -header-to-print %S/Inputs/bridging-header.h -import-objc-header %S/Inputs/bridging-header.h -source-filename=%s -cxx-interoperability-mode=upcoming-swift | %FileCheck %s
+
+// CHECK: struct InBridgingHeader1
+// CHECK: struct InBridgingHeader2