Implement SE-0200 (extended escaping in string literals)

Supports string literals like #"foo"\n"bar"#.

include/swift/Parse/Lexer.h

@@ -364,12 +364,13 @@ public:
     enum : char { Literal, Expr } Kind;
     // Loc+Length for the segment inside the string literal, without quotes.
     SourceLoc Loc;
-    unsigned Length, IndentToStrip;
+    unsigned Length, IndentToStrip, CustomDelimiterLen;
     bool IsFirstSegment, IsLastSegment;
 
     static StringSegment getLiteral(SourceLoc Loc, unsigned Length,
                                     bool IsFirstSegment, bool IsLastSegment,
-                                    unsigned IndentToStrip) {
+                                    unsigned IndentToStrip,
+                                    unsigned CustomDelimiterLen) {
       StringSegment Result;
       Result.Kind = Literal;
       Result.Loc = Loc;
@@ -377,6 +378,7 @@ public:
       Result.IsFirstSegment = IsFirstSegment;
       Result.IsLastSegment = IsLastSegment;
       Result.IndentToStrip = IndentToStrip;
+      Result.CustomDelimiterLen = CustomDelimiterLen;
       return Result;
     }
     
@@ -388,6 +390,7 @@ public:
       Result.IsFirstSegment = false;
       Result.IsLastSegment = false;
       Result.IndentToStrip = 0;
+      Result.CustomDelimiterLen = 0;
       return Result;
     }
 
@@ -404,13 +407,14 @@ public:
                                            SmallVectorImpl<char> &Buffer,
                                            bool IsFirstSegment = false,
                                            bool IsLastSegment = false,
-                                           unsigned IndentToStrip = 0);
+                                           unsigned IndentToStrip = 0,
+                                           unsigned CustomDelimiterLen = 0);
   StringRef getEncodedStringSegment(StringSegment Segment,
                                     SmallVectorImpl<char> &Buffer) const {
     return getEncodedStringSegment(
         StringRef(getBufferPtrForSourceLoc(Segment.Loc), Segment.Length),
         Buffer, Segment.IsFirstSegment, Segment.IsLastSegment,
-        Segment.IndentToStrip);
+        Segment.IndentToStrip, Segment.CustomDelimiterLen);
   }
 
   /// \brief Given a string literal token, separate it into string/expr segments
@@ -474,7 +478,8 @@ private:
     return diagnose(Loc, Diagnostic(DiagID, std::forward<ArgTypes>(Args)...));
   }
 
-  void formToken(tok Kind, const char *TokStart, bool MultilineString = false);
+  void formToken(tok Kind, const char *TokStart, bool IsMultilineString = false,
+                 unsigned CustomDelimiterLen = 0);
   void formEscapedIdentifierToken(const char *TokStart);
 
   /// Advance to the end of the line.
@@ -498,10 +503,10 @@ private:
   void lexTrivia(syntax::Trivia &T, bool IsForTrailingTrivia);
   static unsigned lexUnicodeEscape(const char *&CurPtr, Lexer *Diags);
 
-  unsigned lexCharacter(const char *&CurPtr,
-                        char StopQuote, bool EmitDiagnostics,
-                        bool MultilineString = false);
-  void lexStringLiteral();
+  unsigned lexCharacter(const char *&CurPtr, char StopQuote,
+                        bool EmitDiagnostics, bool IsMultilineString = false,
+                        unsigned CustomDelimiterLen = 0);
+  void lexStringLiteral(unsigned CustomDelimiterLen = 0);
   void lexEscapedIdentifier();
 
   void tryLexEditorPlaceholder();

include/swift/Parse/Token.h

@@ -45,7 +45,10 @@ class Token {
   /// Modifiers for string literals
   unsigned MultilineString : 1;
 
-  // Padding bits == 32 - sizeof(Kind) * 8 - 3;
+  /// Length of custom delimiter of "raw" string literals
+  unsigned CustomDelimiterLen : 8;
+
+  // Padding bits == 32 - 11;
 
   /// \brief The length of the comment that precedes the token.
   unsigned CommentLength;
@@ -62,8 +65,8 @@ class Token {
 public:
   Token(tok Kind, StringRef Text, unsigned CommentLength = 0)
           : Kind(Kind), AtStartOfLine(false), EscapedIdentifier(false),
-            MultilineString(false), CommentLength(CommentLength),
-            Text(Text) {}
+            MultilineString(false), CustomDelimiterLen(0),
+            CommentLength(CommentLength), Text(Text) {}
 
   Token() : Token(tok::NUM_TOKENS, {}, 0) {}
 
@@ -266,17 +269,24 @@ public:
 
   /// \brief Set the token to the specified kind and source range.
   void setToken(tok K, StringRef T, unsigned CommentLength = 0,
-                bool MultilineString = false) {
+                bool IsMultilineString = false, unsigned CustomDelimiterLen = 0) {
     Kind = K;
     Text = T;
     this->CommentLength = CommentLength;
     EscapedIdentifier = false;
-    this->MultilineString = MultilineString;
+    this->MultilineString = IsMultilineString;
+    this->CustomDelimiterLen = CustomDelimiterLen;
+    assert(this->CustomDelimiterLen == CustomDelimiterLen &&
+           "custom string delimiter length > 255");
   }
 
-  bool IsMultilineString() const {
+  bool isMultilineString() const {
     return MultilineString;
   }
+
+  unsigned getCustomDelimiterLen() const {
+    return CustomDelimiterLen;
+  }
 };
   
 } // end namespace swift