I think my tails library could be a good place to put this solution: Tails - Tailwind & Tailwind Component Utilities

We can make classes into a macro instead of a function, and support something like this:

classes(["foo-#{x}", ...], x: [1, 2, 3, 4, 10, 24, 96])

Then it would yell if you interpolate a variable in your classes but don’t provide a list of possible values. Then it would write the file that you’ve mentioned.

Yep! We shouldn’t scan source code, we should provide a macro or sigil that does the validation. The tails library solves for class merging and conditional classes. Class merging is necessary for allowing components to have their classes overridden by parents passing down classes(my preferred way of overriding components) and tails will do a semantic merge based on what classes “conflict” in tailwind.

I’m already working on a macro version of classes as well as a sigil. The macro version will, for now, warn on interpolation unless possible values for the interpolated expression is provided.

Oh my god, just banged my head for a few hours to understand that this is happening.

The thing is that this is not only not consistent, if you use same classes elsewhere, it will work (this also includes cached builds), but it also doesn’t show any kind of errors or warnings.

Actually as it currently stands, it seems that the limitation is that the string should be known at compile-time, things such as this work:

<div class={[@badge_type]}>
</div>

badge_type = get_badge(type)
assign(socket, badge_type: badge_type)

defp badge_type (type) do
    case type do
      :success -> "badge-success"
      :warning -> "badge-warning"
      :error -> "badge-error"
      :inactive -> "badge-ghost"
      :not_found -> "badge-info"
    end
  end

I have both the cases where a separate .heex file is used and when render/1 from an .ex file is used, and both seem to be working when the strings are known at compile-time. Looking at this now, it seems that the configuration watches in .ex files too:

content = [
  ...
  "../lib/*_web/**/*.*ex"
]

Have you found any solutions so somebody else would not stumble onto this bug?