Add swift4 multiline example and update antlr grammar

src/main/antlr/com/sleekbyte/tailor/antlr/Swift.g4

@@ -671,7 +671,7 @@ selectorExpression
 // GRAMMAR OF A KEY PATH EXPRESSION
 
 keyPathExpression
- : '#keyPath' '(' expression ')' 
+ : '#keyPath' '(' expression ')'
  | '\\' expression
 ;
 
@@ -899,7 +899,7 @@ swiftVersion: FloatingPointLiteral ;
 lineControlStatement: '#sourceLocation' '(' 'file' ':' fileName ',' 'line' ':' lineNumber ')'
  | '#sourceLocation' '(' ')' ;
 lineNumber: integerLiteral ;
-fileName: StringLiteral ;
+fileName: SingleStringLiteral ;
 
 // ---------- Lexical Structure -----------
 
@@ -1009,7 +1009,7 @@ ImplicitParameterName : '$' DecimalLiteral ; // TODO: don't allow '_' here
 // GRAMMAR OF A LITERAL
 
 booleanLiteral: BooleanLiteral ;
-literal : numericLiteral | StringLiteral | BooleanLiteral | NilLiteral ;
+literal : numericLiteral | MultiStringLiteral | SingleStringLiteral | BooleanLiteral | NilLiteral ;
 
 // GRAMMAR OF AN INTEGER LITERAL
 
@@ -1060,13 +1060,24 @@ VersionLiteral: DecimalLiteral DecimalFraction DecimalFraction ;
 
 // GRAMMAR OF A STRING LITERAL
 
-StringLiteral : '"' QuotedText? '"' ;
+TRIPLEDQUOTES : '"""' ;
+
+MultiStringLiteral : TRIPLEDQUOTES '\n' .*? '\n' TRIPLEDQUOTES ;
+fragment MultiQuotedText : MultiQuotedTextItem+ ;
+fragment MultiQuotedTextItem : MultiInterpolatedString
+ | ~[\\\u000A\u000D]
+ ;
+fragment MultiInterpolatedString: '\\(' (MultiQuotedTextItem | SingleStringLiteral)* ')';
+
+// StringLiteral : '"' QuotedText? '"' ;
+SingleStringLiteral : '"' QuotedText? '"' ;
+fragment SingleDoubleQuote : '"' | ~["] ;
 fragment QuotedText : QuotedTextItem+ ;
 fragment QuotedTextItem : EscapedCharacter | InterpolatedString
 // | '\\(' expression ')'
  | ~["\\\u000A\u000D]
  ;
-fragment InterpolatedString: '\\(' (QuotedTextItem | StringLiteral)* ')';
+fragment InterpolatedString: '\\(' (QuotedTextItem | SingleStringLiteral)* ')';
 
 EscapedCharacter : '\\' [0\\tnr"']
  | '\\x' HexadecimalDigit HexadecimalDigit

src/test/swift/com/sleekbyte/tailor/grammar/StringsAndCharacters.swift

@@ -3,6 +3,26 @@ let someString = "Some string literal value"
 var emptyString = ""               // empty string literal
 var anotherEmptyString = String()  // initializer syntax
 
+let star = "⭐️"
+
+let multilineString = """
+multiline
+text
+"""
+
+let multilineStringWithVar = """
+multiline
+text
+with a star \(star)
+"""
+
+let multilineStringWithEscaped = """
+  You could write multi-lined strings
+  without "escaping" single quotes.
+"""
+
+
+
 if emptyString.isEmpty {
     print("Nothing to see here")
 }