Simpler lookahead, let the tryParse do the hard work

Author: rbuckton

src/compiler/parser.ts

@@ -3221,34 +3221,13 @@ module ts {
  }
  }
 
- // If encounter "([", this could be the start of an array binding pattern.
+ // If encounter "([" or "({", this could be the start of a binding pattern.
  // Examples:
  // ([ x ]) => { }
- // ([ x ])
- if (second === SyntaxKind.OpenBracketToken) {
- // If the next token is not ",", "...", "[", "{", or an identifier, then this could either be
- // an arrow function with an array binding pattern or a parenthesized array literal expression. 
- // Otherwise, it cannot be an array binding pattern.
- let third = nextToken();
- if (isIdentifierOrPattern() || third === SyntaxKind.CommaToken || third === SyntaxKind.DotDotDotToken) {
- return Tristate.Unknown;
- }
-
- return Tristate.False;
- }
-
- // If we encounter "({", this could be the start of an object binding pattern.
- // Examples:
  // ({ x }) => { }
+ // ([ x ])
  // ({ x })
- // ({ *x() { })
- if (second === SyntaxKind.OpenBraceToken) {
- // If we encountered an asterisk, then this is a generator method on an 
- // object literal and cannot be a binding pattern.
- if (nextToken() === SyntaxKind.AsteriskToken) {
- return Tristate.False;
- }
-
+ if (second === SyntaxKind.OpenBracketToken || second === SyntaxKind.OpenBraceToken) {
  return Tristate.Unknown;
  }