How would you pretty-print an HBS file? Here are some examples of cases that aren't quite cut-and-dry

component-with-many-properties.hbs

{{! All on one line? }}
{{#some-component className='foo bar bax' foo='bar' baz='foo bar baz' somethingElse='some other really long thing'}}

{{/some-component}}

{{! One property per line? (One level of indentation) }}
{{#some-component
  className='foo bar bax'
  foo='bar'
  baz='foo bar baz'
  somethingElse='some other really long thing'
}}

{{/some-component}}

{{! One property per line? (Two levels of indentation) }}
{{! I think this is my favorite because two levels make it more clear where the component begins }}
{{#some-component
    className='foo bar bax'
    foo='bar'
    baz='foo bar baz'
    somethingElse='some other really long thing'
}}

{{/some-component}}

helpers-in-properties.hbs

{{#some-component foo=(if someCondition 'some property' 'some other property') bar='baz'}}
{{/some-component}}

{{! vs }}

{{#some-component
    foo=(if someCondition
      'some property'
      'some other property')
    bar='baz'
}}
{{/some-component}}

{{! vs }}

{{#some-component
    foo=(if someCondition
      'some property'
      'some other property'
    )
    bar='baz'
}}
{{/some-component}}

{{! Also, what do you do with hash helpers? }}

{{#some-component foo=(hash some='prop' other='prop') bar='baz'}}
{{/some-component}}

{{#some-component
    foo=(hash
      some='prop'
      other='prop')
    bar='baz'
}}
{{/some-component}}

{{#some-component
    foo=(hash
      some='prop'
      other='prop'
    )
    bar='baz'
}}
{{/some-component}}

yield-with-many-props.hbs

{{#some-component
    className='foo bar bax'
    foo='bar'
    baz='foo bar baz'
    somethingElse='some other really long thing' as |foo|
}}
{{/some-component}}

{{! vs }}

{{#some-component
    className='foo bar bax'
    foo='bar'
    baz='foo bar baz'
    somethingElse='some other really long thing'
    as |foo|
}}
{{/some-component}}

Another thing to think about: the "named block RFC" will add new syntax that doesn't currently exist in Ember,, but should be accounted for (eventually)

https://github.com/emberjs/rfcs/blob/master/text/0226-named-blocks.md

And yet another thing to think about: Ember will be switching to PascalCase for component names, a la React

<SomeComponent somePositionalParam prop='value'>
</SomeComponent>

This is (somewhat) similar to JSX but is really still Handlebars. Just another thing to think about since components in that form will also (eventually) need support. I can't find a link to anything referencing this at the moment, but I know this change was made to Glimmer and will eventually come to Ember once it can interoperate with Glimmer components.