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+// rust-linemap.h -- interface to location tracking   -*- C++ -*-
+
+// Copyright 2011 The Go Authors. All rights reserved.
+// Copyright (C) 2020-2022 Free Software Foundation, Inc.
+
+// Use of this source code is governed by a BSD-style
+// license that can be found in the '../go/gofrontend/LICENSE' file.
+
+#ifndef RUST_LINEMAP_H
+#define RUST_LINEMAP_H
+
+#include "rust-system.h"
+
+// The backend must define a type named Location which holds
+// information about a location in a source file.  The only thing the
+// frontend does with instances of Location is pass them back to the
+// backend interface.  The Location type must be assignable, and it
+// must be comparable: i.e., it must support operator= and operator<.
+// The type is normally passed by value rather than by reference, and
+// it should support that efficiently.  The type should be defined in
+// "rust-location.h".
+#include "rust-location.h"
+
+// The Linemap class is a pure abstract interface, plus some static
+// convenience functions.  The backend must implement the interface.
+
+/* TODO: probably better to replace linemap implementation as pure abstract
+ * interface with some sort of compile-time switch (macros or maybe templates if
+ * doable without too much extra annoyance) as to the definition of the methods
+ * or whatever. This is to improve performance, as virtual function calls would
+ * otherwise have to be made in tight loops like in the lexer. */
+
+class Linemap
+{
+public:
+  Linemap ()
+  {
+    // Only one instance of Linemap is allowed to exist.
+    rust_assert (Linemap::instance_ == NULL);
+    Linemap::instance_ = this;
+  }
+
+  virtual ~Linemap () { Linemap::instance_ = NULL; }
+
+  // Subsequent Location values will come from the file named
+  // FILE_NAME, starting at LINE_BEGIN.  Normally LINE_BEGIN will be
+  // 0, but it will be non-zero if the Rust source has a //line comment.
+  virtual void start_file (const char *file_name, unsigned int line_begin) = 0;
+
+  // Subsequent Location values will come from the line LINE_NUMBER,
+  // in the current file.  LINE_SIZE is the size of the line in bytes.
+  // This will normally be called for every line in a source file.
+  virtual void start_line (unsigned int line_number, unsigned int line_size)
+    = 0;
+
+  // Get a Location representing column position COLUMN on the current
+  // line in the current file.
+  virtual Location get_location (unsigned int column) = 0;
+
+  // Stop generating Location values.  This will be called after all
+  // input files have been read, in case any cleanup is required.
+  virtual void stop () = 0;
+
+  // Produce a human-readable description of a Location, e.g.
+  // "foo.rust:10". Returns an empty string for predeclared, builtin or
+  // unknown locations.
+  virtual std::string to_string (Location) = 0;
+
+  // Return the file name for a given location.
+  virtual std::string location_file (Location) = 0;
+
+  // Return the line number for a given location.
+  virtual int location_line (Location) = 0;
+
+  // Return the column number for a given location.
+  virtual int location_column (Location) = 0;
+
+protected:
+  // Return a special Location used for predeclared identifiers.  This
+  // Location should be different from that for any actual source
+  // file.  This location will be used for various different types,
+  // functions, and objects created by the frontend.
+  virtual Location get_predeclared_location () = 0;
+
+  // Return a special Location which indicates that no actual location
+  // is known.  This is used for undefined objects and for errors.
+  virtual Location get_unknown_location () = 0;
+
+  // Return whether the argument is the Location returned by
+  // get_predeclared_location.
+  virtual bool is_predeclared (Location) = 0;
+
+  // Return whether the argument is the Location returned by
+  // get_unknown_location.
+  virtual bool is_unknown (Location) = 0;
+
+  // The single existing instance of Linemap.
+  static Linemap *instance_;
+
+public:
+  // Following are convenience static functions, which allow us to
+  // access some virtual functions without explicitly passing around
+  // an instance of Linemap.
+
+  // Return the special Location used for predeclared identifiers.
+  static Location predeclared_location ()
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->get_predeclared_location ();
+  }
+
+  // Return the special Location used when no location is known.
+  static Location unknown_location ()
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->get_unknown_location ();
+  }
+
+  // Return whether the argument is the special location used for
+  // predeclared identifiers.
+  static bool is_predeclared_location (Location loc)
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->is_predeclared (loc);
+  }
+
+  // Return whether the argument is the special location used when no
+  // location is known.
+  static bool is_unknown_location (Location loc)
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->is_unknown (loc);
+  }
+
+  // Produce a human-readable description of a Location.
+  static std::string location_to_string (Location loc)
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->to_string (loc);
+  }
+
+  // Return the file name of a location.
+  static std::string location_to_file (Location loc)
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->location_file (loc);
+  }
+
+  // Return line number of a location.
+  static int location_to_line (Location loc)
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->location_line (loc);
+  }
+
+  static int location_to_column (Location loc)
+  {
+    rust_assert (Linemap::instance_ != NULL);
+    return Linemap::instance_->location_column (loc);
+  }
+};
+
+#endif // !defined(RUST_LINEMAP_H)