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diff --git a/gcc/rust/ast/rust-ast-fragment.h b/gcc/rust/ast/rust-ast-fragment.h
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+++ b/gcc/rust/ast/rust-ast-fragment.h
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+// Copyright (C) 2020-2022 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_AST_FRAGMENT_H
+#define RUST_AST_FRAGMENT_H
+
+#include "rust-ast.h"
+#include "rust-system.h"
+
+namespace Rust {
+namespace AST {
+
+enum class FragmentKind
+{
+  /**
+   * If an AST Fragment still contains unexpanded tokens - this should only be
+   * used in the case of builtin macros which need to be expanded eagerly.
+   */
+  Unexpanded,
+  /**
+   * A completely expanded AST Fragment. This signifies that all
+   * `SingleASTNode`s in the `nodes` vector are valid.
+   *
+   * Note that this doesn't imply that the expansion is "done". One of the
+   * expanded nodes could very well be another macro invocation
+   */
+  Complete,
+  /**
+   * An error fragment.
+   */
+  Error,
+};
+
+/**
+ * An AST Fragment. Previously named `ASTFragment`.
+ *
+ * Basically, a "fragment" that can be incorporated into the AST, created as
+ * a result of macro expansion. Really annoying to work with due to the fact
+ * that macros can really expand to anything. As such, horrible representation
+ * at the moment.
+ */
+class Fragment
+{
+public:
+  Fragment (Fragment const &other);
+  Fragment &operator= (Fragment const &other);
+
+  /**
+   * Create an error fragment
+   */
+  static Fragment create_error ();
+
+  /**
+   * Create a complete AST fragment
+   */
+  static Fragment complete (std::vector<AST::SingleASTNode> nodes);
+
+  /**
+   * Create a fragment which contains unexpanded nodes
+   */
+  static Fragment unexpanded ();
+
+  FragmentKind get_kind () const;
+  std::vector<SingleASTNode> &get_nodes ();
+
+  bool is_error () const;
+  bool should_expand () const;
+
+  bool is_expression_fragment () const;
+  bool is_type_fragment () const;
+
+  std::unique_ptr<Expr> take_expression_fragment ();
+  std::unique_ptr<Type> take_type_fragment ();
+
+  void accept_vis (ASTVisitor &vis);
+
+private:
+  Fragment (FragmentKind kind, std::vector<SingleASTNode> nodes);
+
+  FragmentKind kind;
+
+  /**
+   * Basic idea: essentially, a vector of tagged unions of different AST node
+   * types. Now, this could actually be stored without a tagged union if the
+   * different AST node types had a unified parent, but that would create
+   * issues with the diamond problem or significant performance penalties. So
+   * a tagged union had to be used instead. A vector is used to represent the
+   * ability for a macro to expand to two statements, for instance.
+   */
+  std::vector<SingleASTNode> nodes;
+
+  /**
+   * We need to make a special case for Expression and Type fragments as only
+   * one Node will be extracted from the `nodes` vector
+   */
+  bool is_single_fragment () const;
+  bool is_single_fragment_of_kind (SingleASTNode::NodeType expected) const;
+  void assert_single_fragment (SingleASTNode::NodeType expected) const;
+};
+} // namespace AST
+} // namespace Rust
+
+#endif // !RUST_AST_FRAGMENT_H