Syntax highlighting inside custom string interpolators

Language Design
8

Thinking more about it, I think it should work like this:

// Scala parser, this is a scala file
val dependent = 
  // v search for a syntax highlighter for "html" / ".html" (no compilation need)
  html"""
    // HTML syntax highlighter
    <button ...>
      // `${` detected, switching back to Scala highlighter
      ${ 
        if debug then "" else
          // v search html syntax highlighter
          html"
            // HTML syntax highlighter
            <MyDebug>
               // `${` detected, switching back to Scala highlighter
               ${debugInfo}
               // `}` detected, going back to previous highlighter (HTML)
            </MyDebug>"
          // end of string, going back to scala highlighter
      }
      // `}` detected, going back to previous highlighter (HTML)

   </button>
  """
// end of string, going back to scala highlighter

Here is what would be given to the different highlighters (more or less):

scala:

val dependent = html"""dummy"""

html:

<button ...>
  dummy
</button>

scala:

if debug then "" else html"dummy"

html:

<MyDebug>dummy</MyDebug>

scala:

debugInfo

Or potentially something like the following so the LSPs know where variables come from:
scala:

val dependent = html"""${if debug then "" else html"${debugInfo}"}"""

html:

<button ...>
  <MyDebug>dummy</MyDebug>
</button>

This of course places limitations on what can be highlighted, the following would not (and should not ?) work:

val part1 = html"<bu"
val part2 = html"tton/>"
val sum = part1 + part2

In my mind this is a good thing, JSX-like libraries should not allow you to break the sub-language’s semantics (and to my knowledge JSX doesn’t)