From 2409e339281959fa7fd26e44e80d985922558990 Mon Sep 17 00:00:00 2001
From: Egor Zhdan <e_zhdan@apple.com>
Date: Fri, 22 Aug 2025 17:51:38 +0100
Subject: [PATCH] [cxx-interop] Fix an assertion for `extern "C"` blocks

rdar://158896622 / resolves https://github.com/swiftlang/swift/issues/83861
---
 lib/AST/ASTMangler.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/AST/ASTMangler.cpp b/lib/AST/ASTMangler.cpp
index b7f53971dcc8b..b3fc1430b35fd 100644
--- a/lib/AST/ASTMangler.cpp
+++ b/lib/AST/ASTMangler.cpp
@@ -2560,6 +2560,8 @@ ASTMangler::getSpecialManglingContext(const ValueDecl *decl,
         hasNameForLinkage = !clangDecl->getDeclName().isEmpty();
       if (hasNameForLinkage) {
         auto *clangDC = clangDecl->getDeclContext();
+        while (isa<clang::LinkageSpecDecl>(clangDC))
+          clangDC = clangDC->getParent();
         // In C, "nested" structs, unions, enums, etc. will become siblings:
         //   struct Foo { struct Bar { }; }; -> struct Foo { }; struct Bar { };
         // Whereas in C++, nested records will actually be nested. So if this is