From bf8c94f0f9ea58f04fd96c88039b45cc8cb35add Mon Sep 17 00:00:00 2001
From: David Blaikie <dblaikie@gmail.com>
Date: Mon, 23 Mar 2026 16:44:55 -0700
Subject: [PATCH] Update toolchain/check/cpp/generate_ast.cpp

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
---
 toolchain/check/cpp/generate_ast.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/toolchain/check/cpp/generate_ast.cpp b/toolchain/check/cpp/generate_ast.cpp
index 81eb358349bf..1ba626c68344 100644
--- a/toolchain/check/cpp/generate_ast.cpp
+++ b/toolchain/check/cpp/generate_ast.cpp
@@ -468,6 +468,7 @@ auto CarbonExternalASTSource::FindExternalVisibleDeclsByName(
   }
 
   // Map the found Carbon entity to a Clang NamedDecl.
+  // Use the key to reach the owned, mutable copy of decl_context.
   auto* clang_decl = MapInstIdToClangDecl(*decl_context_inst_id.key(), result);
   if (!clang_decl) {
     return false;