From f588ecb28834eeb9266a3bb03266f82709982278 Mon Sep 17 00:00:00 2001
From: Simon Lydell <simon.lydell@gmail.com>
Date: Tue, 25 Aug 2015 19:19:21 +0200
Subject: [PATCH] Fix #4070: Improve error message for lone expansion

---
 lib/coffee-script/nodes.js |  6 +++++-
 src/nodes.coffee           |  5 ++++-
 test/error_messages.coffee | 16 ++++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/lib/coffee-script/nodes.js b/lib/coffee-script/nodes.js
index 4b940dd7..e71e0881 100644
--- a/lib/coffee-script/nodes.js
+++ b/lib/coffee-script/nodes.js
@@ -1725,8 +1725,12 @@
           return code;
         }
       }
+      obj = objects[0];
+      if (olen === 1 && obj instanceof Expansion) {
+        obj.error('Destructuring assignment has no target');
+      }
       isObject = this.variable.isObject();
-      if (top && olen === 1 && !((obj = objects[0]) instanceof Splat)) {
+      if (top && olen === 1 && !(obj instanceof Splat)) {
         if (obj instanceof Assign) {
           ref3 = obj, (ref4 = ref3.variable, idx = ref4.base), obj = ref3.value;
         } else {
diff --git a/src/nodes.coffee b/src/nodes.coffee
index 42f0fd58..39b8d268 100644
--- a/src/nodes.coffee
+++ b/src/nodes.coffee
@@ -1234,8 +1234,11 @@ exports.Assign = class Assign extends Base
     unless olen = objects.length
       code = value.compileToFragments o
       return if o.level >= LEVEL_OP then @wrapInBraces code else code
+    [obj] = objects
+    if olen is 1 and obj instanceof Expansion
+      obj.error 'Destructuring assignment has no target'
     isObject = @variable.isObject()
-    if top and olen is 1 and (obj = objects[0]) not instanceof Splat
+    if top and olen is 1 and obj not instanceof Splat
       # Unroll simplest cases: `{v} = x` -> `v = x.v`
       if obj instanceof Assign
         {variable: {base: idx}, value: obj} = obj
diff --git a/test/error_messages.coffee b/test/error_messages.coffee
index 50b60a4d..75fb2531 100644
--- a/test/error_messages.coffee
+++ b/test/error_messages.coffee
@@ -776,3 +776,19 @@ test "invalid object keys", ->
       @a: 1
       ^^
   '''
+
+test "#4070: lone expansion", ->
+  assertErrorFormat '''
+    [...] = a
+  ''', '''
+    [stdin]:1:2: error: Destructuring assignment has no target
+    [...] = a
+     ^^^
+  '''
+  assertErrorFormat '''
+    [ ..., ] = a
+  ''', '''
+    [stdin]:1:3: error: Destructuring assignment has no target
+    [ ..., ] = a
+      ^^^
+  '''