Nodes: array destructuring is broken in some cases and leads to TypeError

[adrian-gierakowski]

bug report

when destructuring an array into properties on this, in some cases incorrect code is generated which leads to runtime error when executed

Input Code

array = [ 1, 2, 3, 4, 5 ]

[ @all_but_last_two... , @penultimate, @last ] = array

Expected Behavior

array is correctly destructured and running the code should not lead to runtime error

Current Behavior

running the code leads to following runtime error:

TypeError: Array.prototype.splice called on null or undefined

js code produced by CS 2.2.2:

// Generated by CoffeeScript 2.2.2
(function() {
  var array,
    splice = [].splice;

  array = [1, 2, 3, 4, 5];

  [...this.all_but_last_two] = array, [this.penultimate, this.last] = splice.call(undefined, -2);

}).call(this);

note the splice.call(undefined, -2); which should have been splice.call(this.all_but_last_two, -2);

Additional Notes

output from CS 2.1.1 ( which works as expected )

// Generated by CoffeeScript 2.1.1
(function() {
  var array, i,
    slice = [].slice;

  array = [1, 2, 3, 4, 5];

  this.all_but_last_two = 3 <= array.length ? slice.call(array, 0, i = array.length - 2) : (i = 0, []), this.penultimate = array[i++], this.last = array[i++];

}).call(this);

The bug has probably been introduced by #4825.

if we change @all_but_last_two to all_but_last_two the problem disappears

// Generated by CoffeeScript 2.2.2
(function() {
  var all_but_last_two, array,
    splice = [].splice;

  array = [1, 2, 3, 4, 5];

  [...all_but_last_two] = array, [this.penultimate, this.last] = splice.call(all_but_last_two, -2);

}).call(this);

Environment

• CoffeeScript version: 2.2.2
• Node.js version: 8.9.4