This is outside the scope of this PR, but I think it would be beneficial to keep as_ref as a usable option for backward compatibility. Something like this could work as a temporary solution:

// filters.rs:45
"as_ref" => {
    eprintln!(
        "Warning: `as_ref` is deprecated and has been renamed to `ref`. Please update your templates."
    );
    Self::visit_ref_filter
}

That said, printing to stderr isn’t ideal. It would be great to emit proper deprecation warnings directly in the template output, for example:

warning: `as_ref` is deprecated and has been renamed to `ref`. Please update your templates.
  ┌─ index.html:12:15
  │
12 │ <p>{{ foo | as_ref }}</p>
  │               ^^^^^^ `as_ref` is deprecated and has been renamed to `ref`. Please update your templates.

However, implementing this kind of contextual warning would likely require some changes to the current code 😑

Thanks!