Improve binding patterns for arrow functions

lib/parse.js

@@ -1232,6 +1232,10 @@ function parse($TEXT, options) {
     };
 
     var arrow_function = function(args) {
+        if (S.token.nlb) {
+            croak("SyntaxError: Unexpected newline before arrow (=>)");
+        }
+
         expect_token("arrow", "=>");
 
         var argnames;
@@ -1425,12 +1429,13 @@ function parse($TEXT, options) {
                 if (is("punc")) {
                     switch (S.token.value) {
                       case ",":
-                      case "]": // Last element
                         elements.push(new AST_Hole({
                             start: S.token,
                             end: S.token
                         }));
                         continue;
+                      case "]": // Trailing comma after last element
+                        break;
                       case "[":
                       case "{":
                         elements.push(binding_element(used_parameters, symbol_type));
@@ -1560,7 +1565,7 @@ function parse($TEXT, options) {
                 next();
                 a.push(new AST_Expansion({
                     start: prev(),
-                    expression: as_symbol(AST_SymbolFunarg),
+                    expression: binding_element(undefined, AST_SymbolFunarg),
                     end: S.token,
                 }));
                 if (!is("punc", ")")) {
@@ -2011,15 +2016,13 @@ function parse($TEXT, options) {
                 // It's one of those object destructurings, the value is its own name
                 a.push(new AST_ObjectKeyVal({
                     start: start,
-                    quote: start.quote,
-                    end: start,
                     key: name,
                     value: new AST_SymbolRef({
                         start: start,
-                        end: start,
+                        end: prev(),
                         name: name
                     }),
-                    shorthand: true,
+                    end: start,
                 }));
             } else {
                 expect(":");