restructure testing infrastructure to be more modular

src/expression.js

@@ -101,6 +101,13 @@ pp.parseMaybeAssign = function(noIn, refShorthandDefaultPos, afterLeftParse) {
     node.left = this.type === tt.eq ? this.toAssignable(left) : left
     refShorthandDefaultPos.start = 0; // reset because shorthand default was used correctly
     this.checkLVal(left)
+    if (left.parenthesizedExpression) {
+      if (left.type === "ObjectPattern") {
+        this.raise(left.start, "You're trying to assign to a parenthesized expression, instead of `({ foo }) = {}` use `({ foo } = {})`");
+      } else {
+        this.raise(left.start, "Parenthesized left hand expressions are illegal");
+      }
+    }
     this.next()
     node.right = this.parseMaybeAssign(noIn)
     return this.finishNode(node, "AssignmentExpression")

src/lval.js

@@ -9,14 +9,6 @@ const pp = Parser.prototype
 // if possible.
 
 pp.toAssignable = function(node, isBinding) {
-  if (node.parenthesizedExpression) {
-    if (node.type === "ObjectExpression") {
-      this.raise(node.start, "You're trying to assign to a parenthesized expression, instead of `({ foo }) = {}` use `({ foo } = {})`");
-    } else {
-      this.raise(node.start, "Parenthesized left hand expressions are illegal");
-    }
-  }
-
   if (this.options.ecmaVersion >= 6 && node) {
     switch (node.type) {
     case "Identifier":

src/tokencontext.js

@@ -57,6 +57,10 @@ pp.updateContext = function(prevType) {
 // Token-specific context update code
 
 tt.parenR.updateContext = tt.braceR.updateContext = function() {
+  if (this.context.length == 1) {
+    this.exprAllowed = true
+    return
+  }
   let out = this.context.pop()
   if (out === types.b_stat && this.curContext() === types.f_expr) {
     this.context.pop()
@@ -64,7 +68,7 @@ tt.parenR.updateContext = tt.braceR.updateContext = function() {
   } else if (out === types.b_tmpl) {
     this.exprAllowed = true
   } else {
-    this.exprAllowed = !(out && out.isExpr)
+    this.exprAllowed = !out.isExpr
   }
 }