straightforward port of rust mockup code

src/libutil/error.hh

@@ -0,0 +1,57 @@
+#pragma once
+
+#include "types.hh"
+#include <string>
+#include <optional>
+// #include <boost/format.hpp>
+
+using std::string;
+using std::optional;
+// using boost::format;
+
+namespace nix {
+
+enum ErrLevel 
+  { elWarning
+  , elError
+  };
+
+class ColumnRange { 
+  public:
+  unsigned int start;
+  unsigned int len;
+};
+
+class ErrLine { 
+  public:
+  int lineNumber;
+  optional<ColumnRange> columnRange;
+  optional<string> prevLineOfCode;
+  string errLineOfCode;
+  optional<string> nextLineOfCode;
+};
+
+class NixCode { 
+  public:
+  optional<string> nixFile;
+  optional<ErrLine> errLine;
+};
+
+
+class ErrorInfo { 
+  public:
+  ErrLevel level;
+  string errName;
+  string description;
+  string toolName;
+  optional<NixCode> nixCode;
+  string hint;
+};
+
+string showErrLine(ErrLine &errLine);
+
+void print_code_lines(string &prefix, NixCode &nix_code); 
+
+void print_error(ErrorInfo &einfo);
+}
+