Tree-shaking extension fails for non-named imports

[mjstahl]

Assuming an imported file helpers/helpers.js that includes a handfull of imports like so:

// helpers/helpers.js
import 'a.js'
import 'b.js'

In a stache file, use can-import to import the helpers file

<!-- index.stache -->
<can-import from="~/helpers/" />

When loading that stache file the following error will occur.

This error occurs at https://github.com/stealjs/steal/blob/2488567bcb55a38958ba3877a280ad7202d3e28c/src/extension-tree-shaking.js#L106 because parentImportNames (parentLoad.metadata.importNames) is undefined.

A work around for this is to name the imports.

// helpers/helpers.js
import A from 'a.js'
import B from 'b.js'