[v2.15.0] Bug declaring the same component attribute twice (creates a mutableCell)

Hi, I just updated from 2.14 to 2.15 and found a weird “bug”. By mistake I was rendering a component passing the same attr twice, like this: {{my-component componentVar=myStringVar componentVar=myStringVar}}

I know this makes no sense, but it was working correctly in 2.14 In 2.15 it doesn’t work. Suddenly componentVar is no longer the myStringVar but instead is a mutable cell object.

I created a twiddle with a reproduction, check the console also. https://ember-twiddle.com/c1f4d778120fe303436b0e5df029fcf2

Not saying this should be supported, but maybe throw an error? It can be difficult to debug the way it is.

[esbanarango]

@urbany Now that the latest versions of ember-cli come with ember-template-lint enabled by default It will prevent this issue. I think we can close this now.

[kyleshay]

FYI - there is a new template linter rule against this issue: https://github.com/rwjblue/ember-template-lint/blob/master/docs/rule/no-duplicate-attributes.md