scope names in expressions can collide with other references

[sjmiles]

Please update the issue title as needed, I'm not being super precise.

An expression like this

<polymer-element name="test-element" attributes="property">
<template>
  <template repeat="{{id in ['a', 'b', 'c']}}">

Throws or has unusual behavior when the alias variable (id in this case) corresponds to an HTMLElement built-in.

Repro: http://jsbin.com/wediq/2/edit

Fwiw, I've also seen alias variables affect an element's properties, but I didn't capture the details, I'm working on a repro.

[jmesserly]

just a guess, it could be here:
https://github.com/Polymer/polymer-expressions/blob/master/src/polymer-expressions.js#L570

since it uses Object.create(parentScope) the proto might have a setter.

[arv]

We could replace that with defineProperty but I'm not sure this is the real problem...

[rafaelw]

Yup. That sure looks like (at least one) problem.

[rafaelw]

Fixed in: 2edf01d