Fix bug in entering subscript expressions from an ambiguous obj pattern

When the object had a shorthand defaulted property in it,
that prevented the subscript in the nested expression from
being parsed.

Closes #735

acorn/dist/acorn.d.ts

@@ -42,11 +42,9 @@ declare namespace acorn {
       getToken(): Token
       [Symbol.iterator](): Iterator<Token>
     }
-    static extend(...plugins: Constructor<Parser>[]): Constructor<Parser>
+    static extend(...plugins: (typeof Parser)[]): typeof Parser
   }
 
-  type Constructor<T> = new (...args: any[]) => T
-
   interface Position { line: number; column: number; offset: number }
 
   const defaultOptions: Options

acorn/src/expression.js

@@ -111,11 +111,12 @@ pp.parseMaybeAssign = function(noIn, refDestructuringErrors, afterLeftParse) {
     else this.exprAllowed = false
   }
 
-  let ownDestructuringErrors = false, oldParenAssign = -1, oldTrailingComma = -1
+  let ownDestructuringErrors = false, oldParenAssign = -1, oldTrailingComma = -1, oldShorthandAssign = -1
   if (refDestructuringErrors) {
     oldParenAssign = refDestructuringErrors.parenthesizedAssign
     oldTrailingComma = refDestructuringErrors.trailingComma
-    refDestructuringErrors.parenthesizedAssign = refDestructuringErrors.trailingComma = -1
+    oldShorthandAssign = refDestructuringErrors.shorthandAssign;
+    refDestructuringErrors.parenthesizedAssign = refDestructuringErrors.trailingComma = refDestructuringErrors.shorthandAssign = -1
   } else {
     refDestructuringErrors = new DestructuringErrors
     ownDestructuringErrors = true
@@ -141,6 +142,7 @@ pp.parseMaybeAssign = function(noIn, refDestructuringErrors, afterLeftParse) {
   }
   if (oldParenAssign > -1) refDestructuringErrors.parenthesizedAssign = oldParenAssign
   if (oldTrailingComma > -1) refDestructuringErrors.trailingComma = oldTrailingComma
+  if (oldShorthandAssign > -1) refDestructuringErrors.shorthandAssign = oldShorthandAssign
   return left
 }
 

test/tests-harmony.js

@@ -16249,3 +16249,5 @@ test("a.of / 2", {}, {ecmaVersion: 6})
 test("let x = 1; x = 2", {}, {ecmaVersion: 6})
 
 test("function *f2() { () => yield / 1 }", {}, {ecmaVersion: 6})
+
+test("({ a = 42, b: c.d } = e)", {}, {ecmaVersion: 6})