/// <summary>
/// Converts string literal text into its value. Returns null if the specified string token is malformed due to lexer error recovery.
/// </summary>
/// <param name="stringToken">the string token</param>
public static string?TryGetStringValue(Token stringToken)
{
var(start, end) = stringToken.Type switch {
TokenType.StringComplete => (LanguageConstants.StringDelimiter, LanguageConstants.StringDelimiter),
TokenType.StringLeftPiece => (LanguageConstants.StringDelimiter, LanguageConstants.StringHoleOpen),
TokenType.StringMiddlePiece => (LanguageConstants.StringHoleClose, LanguageConstants.StringHoleOpen),
TokenType.StringRightPiece => (LanguageConstants.StringHoleClose, LanguageConstants.StringDelimiter),
_ => (null, null),
};
if (start == null || end == null)
{
return(null);
}
if (stringToken.Text.Length < start.Length + end.Length ||
stringToken.Text.Substring(0, start.Length) != start ||
stringToken.Text.Substring(stringToken.Text.Length - end.Length) != end)
{
// any lexer-generated token should not hit this problem as the start & end are already verified
return(null);
}
var contents = stringToken.Text.Substring(start.Length, stringToken.Text.Length - start.Length - end.Length);
var window = new SlidingTextWindow(contents);
// the value of the string will be shorter because escapes are longer than the characters they represent
var buffer = new StringBuilder(contents.Length);
while (!window.IsAtEnd())
{
var nextChar = window.Next();
if (nextChar == '\'')
{
return(null);
}
if (nextChar == '\\')
{
// escape sequence begins
if (window.IsAtEnd())
{
return(null);
}
char escapeChar = window.Next();
if (CharacterEscapes.TryGetValue(escapeChar, out char escapeCharValue) == false)
{
// invalid escape character
return(null);
}
buffer.Append(escapeCharValue);
// continue to next iteration
continue;
}
// regular string char - append to buffer
buffer.Append(nextChar);
}
return(buffer.ToString());
}
public Lexer(SlidingTextWindow textWindow)
{
this.textWindow = textWindow;
}
public Lexer(SlidingTextWindow textWindow, IDiagnosticWriter diagnosticWriter)
{
this.textWindow = textWindow;
this.diagnosticWriter = diagnosticWriter;
}