Implement handling of arrow functions in the parser

src/scanner.h

Index: src/scanner.h
diff --git a/src/scanner.h b/src/scanner.h
index 037da5b1739a302cbdda71ce50e82a3055c0d712..2c0f687f6625b2c7f4820b79ab28ab717e8c48c6 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -187,6 +187,84 @@ class DuplicateFinder {
 
 
 // ----------------------------------------------------------------------------
+// ParamListFinder discovers sequences of tokens which form a valid function
+// parameter list.
+
+class ParamListFinder {
+ public:
+  ParamListFinder(): state_(Invalid), start_pos_(-1) { }
+
+  void Update(Token::Value token, int pos) {
+    switch (state_) {
+      case Valid:
+        state_ = Invalid;
+        start_pos_ = -1;
+        // Fall-through.
+      case Invalid:
+        if (token == Token::LPAREN) {
+          state_ = LeftParen;
+          start_pos_ = pos;
+        }
+        break;
+
+      case LeftParen:
+        switch (token) {
+          case Token::LPAREN:
+            start_pos_ = pos;
+            break;
+          case Token::RPAREN:
+            state_ = Valid;
+            break;
+          case Token::IDENTIFIER:
+            state_ = Identifier;
+            break;
+          default:
+            state_ = Invalid;
+        }
+        break;
+
+      case Identifier:
+        switch (token) {
+          case Token::RPAREN:
+            state_ = Valid;
+            break;
+          case Token::COMMA:
+            state_ = Comma;
+            break;
+          default:
+            state_ = Invalid;
+        }
+        break;
+
+      case Comma:
+        if (token == Token::IDENTIFIER) {
+          state_ = Identifier;
+        } else {
+          state_ = Invalid;
+        }
+        break;
+    }
+  }
+
+  bool IsValid(int pos) const {
+    return state_ == Valid && start_pos_ == pos;
+  }
+
+ private:
+  enum State {
+    Invalid,
+    Valid,
+    LeftParen,
+    Identifier,
+    Comma
+  };
+
+  State state_;
+  int start_pos_;
+};
+
+
+// ----------------------------------------------------------------------------
 // LiteralBuffer -  Collector of chars of literals.
 
 class LiteralBuffer {
@@ -402,6 +480,10 @@ class Scanner {
     }
   }
 
+  bool IsValidParameterList(int pos) const {
+      return param_list_finder_.IsValid(pos);
+  }
+
   int FindNumber(DuplicateFinder* finder, int value);
   int FindSymbol(DuplicateFinder* finder, int value);
 
@@ -605,6 +687,8 @@ class Scanner {
   LiteralBuffer literal_buffer1_;
   LiteralBuffer literal_buffer2_;
 
+  ParamListFinder param_list_finder_;
+
   TokenDesc current_;  // desc for current token (as returned by Next())
   TokenDesc next_;     // desc for next token (one token look-ahead)