Rendering <button> in each loop breaks application

In ember 3.3.0 following template breaks application:

{{#each buttons as |button|}}
  <button>{{button}}</button>
{{/each}}

buttons is a simple array. In console I can see Uncaught Error: unreachable. This error does not happen with other tags (i.e. works fine) and does not happen on ember 3.2.2

Repository with demonstration: https://github.com/GendelfLugansk/ember-rendering-bug

[rwjblue]

Is this considered a breaking change?

Yes, it is a breaking change and we are working on the fix.

I’m also a little confused by the RFC as to whether this is allowed (and supposed to work), or allowed at build-time (but breaks at run-time).

The current behavior matches what the RFC stated (essentially that a block param named button + <button></button> in the blocks template, would assume that the block param was a yielded closure component and attempt to render it as such), but based on feedback (here and in other issues) we determined that the result is definitely something we consider a breaking change.

The current plan (after discussing with the core team on 2018-07-20) is:

• Ensure that all block params that “shadow” normal HTML elements inside their blocks, continue to render the HTML element (and do not assume they should “invoke” a yielded component).
• Issue a deprecation when this scenario is detected (with until: '4.0.0')
• Ensure the linter is setup for newly generated Ember apps that will lint against using confusing block param names (where the block param could be an HTML element name, and that HTML element is invoked in the blocks template).
• Backport these fixes to Ember 3.3

[rwjblue]

This change should not have happened during 3.3, and we will try to figure out why it did (and fix it). However, we do intend for it to land as part of 3.4 (along with support for linting in applications as a general guide).