Fix ArgumentOutOfRangeException in GetContextualMessage for empty source #615

[meichenberger78]

Fixes #615

Problem

GetContextualMessage threw an ArgumentOutOfRangeException when the parsed source was empty, because the requested line index was out of range for the lines produced by GetLines().

       protected string GetContextualMessage(string fullSource, int line, int column, string message)
       {
           StringBuilder sb = new StringBuilder();
           sb.AppendLine(ErrorMessage);
           var theLine = fullSource.GetLines()[line];
           var tab = " ".Multiply(line.ToString().Length);
           sb.Append(tab).AppendLine(" |");
           sb.Append(line).Append(" |").AppendLine(theLine);
           sb.Append($"{tab} |").Append(" ".Multiply(column)).Append("^^^").AppendLine($" {message}");
           
           return sb.ToString();
      }

https://github.com/b3b00/csly/blob/dev/src/sly/parser/parser/ParseError.cs#L56

Fix

Added a bounds check before indexing into lines, falling back to an empty string when the line index is out of range.

      protected string GetContextualMessage(string fullSource, int line, int column, string message)
      {
          StringBuilder sb = new StringBuilder();
          sb.AppendLine(ErrorMessage);
          var lines = (fullSource ?? string.Empty).GetLines();
          var theLine = line >= 0 && line < lines.Count ? lines[line] : string.Empty;
          var tab = " ".Multiply(line.ToString().Length);
          sb.Append(tab).AppendLine(" |");
          sb.Append(line).Append(" |").AppendLine(theLine);
          sb.Append($"{tab} |").Append(" ".Multiply(column)).Append("^^^").AppendLine($" {message}");
          
          return sb.ToString();
      }

Testing

Added TestContextualErrorWithEmptySource, which parses an empty string and asserts that no exception is thrown and that a valid 4-line ContextualErrorMessage is produced.

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Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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