This is a follow up fix for
894286dd0c.
It turns out that comments can be closed in several ways:
- `<!-->`
- `<!-- -->`
- `<!-- --!>`
All of the above are valid ways to close comment per:
https://html.spec.whatwg.org/multipage/syntax.html#comments
The new fix surrounds `<` and `>` with zero width space so that it
renders in the same way, but it prevents the comment to be closed eagerly.
PR Close#40525
Escape the content of the strings so that it can be safely inserted into a comment node.
The issue is that HTML does not specify any way to escape comment end text inside the comment.
`<!-- The way you close a comment is with "-->". -->`. Above the `"-->"` is meant to be text
not an end to the comment. This can be created programmatically through DOM APIs.
```
div.innerHTML = div.innerHTML
```
One would expect that the above code would be safe to do, but it turns out that because comment
text is not escaped, the comment may contain text which will prematurely close the comment
opening up the application for XSS attack. (In SSR we programmatically create comment nodes which
may contain such text and expect them to be safe.)
This function escapes the comment text by looking for the closing char sequence `-->` and replace
it with `-_-_>` where the `_` is a zero width space `\u200B`. The result is that if a comment
contains `-->` text it will render normally but it will not cause the HTML parser to close the
comment.
PR Close#40136
Jessica Janiuk
Misko Hevery