How to do it...

  1. Open Roslyn.sln in Visual Studio 2017
  2. Open source file %REPO_ROOT%\src\Compilers\CSharp\Portable\Parser\Lexer.cs and add the highlighted else if statement at line 565 in the method ScanSyntaxToken:
case '?':  if (TextWindow.PeekChar() == '?') { ... } else if (TextWindow.PeekChar() == ':') {  TextWindow.AdvanceChar();  info.Kind = SyntaxKind.QuestionColonToken; } else { ... }
  1. Open source file %REPO_ROOT%\src\Compilers\CSharp\Portable\Parser\LanguageParser.cs and add the highlighted else if statement at line 9426 in the method ParseSubExpressionCore:
if (tk == SyntaxKind.QuestionToken && precedence <= Precedence.Ternary){ ...}else if (tk == SyntaxKind.QuestionColonToken && precedence <= Precedence.Ternary){ var questionColonToken ...

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