Fixes: #4047 (comment)

Issue: #189
RFC: lit/rfcs#21
Full prototype PR: #3984

Why

@rictic pointed out an oversight that the naive logic of minifying empty comments could match and miscompile code if these empty comments were used elsewhere.

Example

The code:

<style>
  div::before {
    content: '<!---->';
  }
  div::after {
    content: '<!--?-->';
  }
</style>
<div>Hello world</div>

Renders: <!---->Hello world<!--?-->.

However when compiled without this fix, the compiled code would result in <?>Hello world<?> rendering.

Fix

Only minify marker comments by matching on <!--lit$12345$--> and converting them to <?>. It's then far less likely to result in a collision.

Test

Added a regression golden test case.