Prettier 2.7.1
Playground link

Input:

<div />
<custom-component />

Output:

<div></div>
<custom-component></custom-component>

Expected behavior:

<div />
<custom-component />

Ember allows for self-closing tags (see docs), but prettier with the glimmer parser adds closing tags instead. I'm not sure if this was a conscious decision, because the JSX parser does convert closing tags.