Update:

After running a mix deps.get, things are all firing
How else would VSCode know

Hi Ben
Sorry to resurrect an old thread.
I’m sitting with the same issue but have ElixirLS installed.

This is my Elixir+Phoenix settings in my settings.json in VSCode.

  // elixir + phoenix

  "elixirLS.suggestSpecs": false,
  "elixirLS.dialyzerEnabled": true,
  "elixirLS.signatureAfterComplete": false,
  "elixirLS.fetchDeps": false,

  "[elixir]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "JakeBecker.elixir-ls"
  },

  "[phoenix-heex]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "JakeBecker.elixir-ls"
  },

  "files.associations": {
    "*.heex": "phoenix-heex",
    "*.exs": "elixir",
    "*.ex": "elixir",
    "**/*.html": "html",
  },

  "emmet.includeLanguages": {
    "phoenix-heex": "html",
    "elixir": "html",
    "html-eex": "html"
  },

  "tailwindCSS.includeLanguages": {
    "phoenix-heex": "html",
    "elixir": "html"
  },

  // elixir + phoenix

Extensions enabled:

Elixir Mix Formatter v1.0.1
ElixirLS: Elixir support and debugger v0.19.0
Phoenix Framework v0.1.2

I might be missing something or probably configured incorrectly…

Thanks
Carl-Heinz