From 828fdc8769a714cd9240ffc1e950d3cf64e2cf2f Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Mon, 13 Apr 2015 16:40:13 -0700
Subject: [PATCH] make illegal LHS pattern error messages more user friendly

---
 src/acorn/src/expression.js | 12 ++++++++++--
 test/acorn/tests-babel.js   |  4 ++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/acorn/src/expression.js b/src/acorn/src/expression.js
index 998864d077..3540956fe3 100755
--- a/src/acorn/src/expression.js
+++ b/src/acorn/src/expression.js
@@ -103,8 +103,16 @@ 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 && (left.type === "ObjectPattern" || left.type === "ArrayPattern")) {
-      this.raise(left.start, "You're trying to assign to a parenthesized expression, instead of `({ foo }) = {}` use `({ foo } = {})`");
+    if (left.parenthesizedExpression) {
+      let errorMsg
+      if (left.type === "ObjectPattern") {
+        errorMsg = "`({a}) = 0` use `({a} = 0)`"
+      } else if (left.type === "ArrayPattern") {
+        errorMsg = "`([a]) = 0` use `([a] = 0)`"
+      }
+      if (errorMsg) {
+        this.raise(left.start, `You're trying to assign to a parenthesized expression, eg. instead of ${errorMsg}`)
+      }
     }
     this.next()
     node.right = this.parseMaybeAssign(noIn)
diff --git a/test/acorn/tests-babel.js b/test/acorn/tests-babel.js
index ef99afd578..ad8d7b3a16 100644
--- a/test/acorn/tests-babel.js
+++ b/test/acorn/tests-babel.js
@@ -2,11 +2,11 @@ var test = require("./driver.js").test;
 var testFail = require("./driver.js").testFail;
 var testAssert = require("./driver.js").testAssert;
 
-testFail("({a}) = 2;", "You're trying to assign to a parenthesized expression, instead of `({ foo }) = {}` use `({ foo } = {})` (1:1)", {
+testFail("({a}) = 2;", "You're trying to assign to a parenthesized expression, eg. instead of `({a}) = 0` use `({a} = {})` (1:1)", {
   ecmaVersion: 6
 });
 
-testFail("([a]) = 2;", "You're trying to assign to a parenthesized expression, instead of `({ foo }) = {}` use `({ foo } = {})` (1:1)", {
+testFail("([a]) = 2;", "You're trying to assign to a parenthesized expression, eg. instead of `([a]) = 0` use `([a] = {})` (1:1)", {
   ecmaVersion: 6
 });