Emmet balance, updatetag failing due to invalid HTML parsing algorithm

[OliverJAsh]

• VSCode Version: 1.46.0
• OS Version: 10.15.5

Steps to Reproduce:

1. Create a tsx file with this content:

   import React from 'react';
   
   // <f
   
   const MyComponent = () => <div className="foo">Hello, World</div>;

2. Highlight the opening tag of div and run any one of these commands:
   • "Emmet: Split/Join Tag"
   • "Emmet: Update Tag"
   • "Emmet: Go to Matching Pair"

Expected: the command should work
Actual: the command does nothing

If we remove the comment that contains <f, it works.

Does this issue occur when all extensions are disabled?: Yes

[OliverJAsh]

Updated issue to mention that this also effects other commands.

[amagupta-collab]

Interested in working on this, will be picking it up

[rzhao271]

The current parser in util.ts is trying to parse f as its own tag, and so I think it needs to be updated. Another instance of this issue is #73415

[rzhao271]

Verifier:

1. Set up a new .tsx file with the contents

import React from 'react';

// <f

const MyComponent = () => <div className="foo">Hello, World</div>;

2. Place cursor on the first div
3. Emmet: Go to Matching Tag should cause the cursor to go to the other div tag.
4. Emmet: Update Tag should bring up a prompt for the new tag name. Enter span. The div tag should have changed to a span tag. The className="foo" part and the inner contents should remain the same.
5. Emmet: Split/Join Tag should collapse the <div className="foo">...</div> into <div className="foo"/>, and then <div className="foo"></div>.