How to force other formatter to be used by MultiFormatter on foreign language?

[aleksusklim]

I am trying to use Multi Formatter Extension to process HTML file to be formatted as JS file and then as HTML file. I believe this is the only way to properly reformat EJS embeds <% %> as normal JS.

When I have a EJS file to be formatted, I can change the language to Javascript and format with native Typescript and Javascript Language Features, all JS embeds are formatted properly but HTML tags get broken; then, if I'll change the language to HTML and format with native HTML Language Features (while also having EJS language support installed) – all HTML is fixed while already pre-formatted JS is preserved.

I thought Multi Formatter Extension could solve this, so I set up

  "html.format.templating": true,
  "emmet.includeLanguages": {
    "ejs": "html",
  },
  "files.associations": {
    "*.ejs": "html"
  },
  "[javascript]": {
    "editor.defaultFormatter": "vscode.typescript-language-features"
  },
  "[html]": {
    "editor.defaultFormatter": "vscode.html-language-features",
    "multiFormatter.formatterList": ["vscode.typescript-language-features", "vscode.html-language-features"]
  },

But unfortunately, I see the error:
Extension 'TypeScript and JavaScript Language Features' is configured as formatter but it cannot format 'HTML'-files

I even tried to edit …\Microsoft VS Code\resources\app\extensions\typescript-language-features\package.json, adding "onLanguage:html", to "activationEvents":[ (just as MultiFormatter does it), and restarted VSCode.

But this changed nothing, and I cannot even choose Typescript and Javascript Language Features as a formatter whenever I have HTML as current language.
(Permanently changing the current language breaks EJS highlighting; I tried other EJS formatters/beautifiers with no avail).

What can I try?
Maybe it is technically possible to swap the language during multiformat itself somehow?

[unimorphic]

Created a new extension that supports multiple languages in a single file, see the Multi Language example in the readme https://github.com/unimorphic/vscode-format-att