Bug: computed properties can fall out of sync with attributes

[klebba]

We have a property definition like this:

open: {
  type: Boolean,
  reflect: true,
  computed: 'computeOpen(model)',
  observer: 'observeOpen',
},

Then we have a demo page with plain HTML like this: <my-element open></my-element> — open should be read only since it’s computed, but we have declared it in the markup accidentally due to a refactor. When I poll the instance of my-element for the value of it's open property the result is undefined which is correct.

The issue though is that the attribute is not removed when the element boots up. This causes a bug where styles which look for my-element[open] are being matched, but the inner template which is binding open to a child element is binding the value undefined

[theengineear]

The new version of x-element will throw an error like this:

Uncaught Error: Property "HelloElement.properties.open" is computed (computed properties are read-only).

I think that fixes your problem one way or another. I'll close this down, but feel free to reopen if you think it's not going to handle this case correctly.