HTMLBars AST does not push CommentStatements?

[step2yeung]

I noticed that HTMLBars AST does not push mustache statement styled comments into the AST, while HandleBars AST does. Is there a reason for this difference?

For example:

{{! comments }}
<div">
  foobar
</div>

Handlebars AST looks like (Notice the CommentStatement element):

{ loc: 
   { source: undefined,
     start: { line: 1, column: 0 },
     end: { line: 5, column: 0 } },
  type: 'Program',
  body: 
   [ { loc: [Object],
       type: 'CommentStatement',
       value: ' comments ',
       strip: [Object] },
     { loc: [Object],
       type: 'ContentStatement',
       value: '<div class="panel">\n  foobar\n</div>\n',
       original: '\n<div class="panel">\n  foobar\n</div>\n',
       rightStripped: true } ],
  blockParams: null,
  strip: {} }

While, HTMLBar AST does not push the comment statement into the AST elements.

{ type: 'Program',
  body: 
   [ { type: 'ElementNode',
       tag: 'div',
       attributes: [Object],
       modifiers: [],
       children: [Object],
       loc: [Object] },
     { type: 'TextNode', chars: '\n', loc: null } ],
  blockParams: [],
  loc: 
   { source: null,
     start: { line: 1, column: 0 },
     end: { line: 5, column: 0 } } }

[mmun]

This is a bug. We need to preserve both HTML and HBS comments.

[zackthehuman]

The more I think about this it actually seems like not a bug. If the objective of HTMLBars' parsing is to produce an AST that ultimately maps to DOM, then preserving Handlebars comments has no meaningful impact on the DOM, unlike HTML comments.

[mmun]

Yes, they are 100% inert but for practical reasons it would be useful to have them in the AST, e.g. for future linting tools. We may opt instead to have a separate Concrete Syntax Tree but my hunch is that there isn't enough differences between the AST and CST to merit the extra complexity.