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diff --git a/gcc/rust/ast/rust-desugar-question-mark.h b/gcc/rust/ast/rust-desugar-question-mark.h
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+// Copyright (C) 2025 Free Software Foundation, Inc.
+
+// This file is part of GCC.
+
+// GCC is free software; you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3, or (at your option) any later
+// version.
+
+// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+// for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with GCC; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#ifndef RUST_DESUGAR_QUESTION_MARK
+#define RUST_DESUGAR_QUESTION_MARK
+
+#include "rust-ast-visitor.h"
+#include "rust-expr.h"
+#include "rust-stmt.h"
+
+namespace Rust {
+namespace AST {
+
+// NOTE: One more complexity compare to desugaring for-loops is that we need to
+// desugar every possible expression... should we do that during lowering
+// instead? but would it get resolved and expanded etc? Not sure...
+
+// The goal of this desugar is to go from this:
+//
+// ```
+// <expr>?
+// ```
+//
+// to this:
+//
+// ```
+// match Try::into_result(<expr>) {
+//   Ok(val) => val,
+//   Err(err) => return Try::from_err(From::from(err))
+// }
+// ```
+//
+// We use lang items for almost everything, so the actual desugared code looks
+// more like this:
+//
+// ```
+// match #[lang = "into_result"](<expr>) {
+//   #[lang = "Ok"](val) => val,
+//   #[lang = "Err"](err) => {
+//     return #[lang = "from_error"](#[lang ="from"](err))
+//   }
+// }
+// ```
+class DesugarQuestionMark : public DefaultASTVisitor
+{
+  using DefaultASTVisitor::visit;
+
+public:
+  DesugarQuestionMark ();
+  void go (AST::Crate &);
+
+private:
+  void desugar_and_replace (std::unique_ptr<Expr> &ptr);
+  std::unique_ptr<Expr> desugar (ErrorPropagationExpr &);
+
+  void visit (AST::ExprStmt &) override;
+  void visit (AST::CallExpr &) override;
+  void visit (AST::LetStmt &) override;
+};
+
+} // namespace AST
+} // namespace Rust
+
+#endif // ! RUST_DESUGAR_QUESTION_MARK