Surface.Formatter.Plugin incompatible with Elixir 1.19.0-rc.0 - Enumerable protocol error for keyword lists #766

Describe the bug

The Surface formatter plugin (v0.12.1) is incompatible with Elixir 1.19.0-rc.0. When running mix format on .sface files, the formatter fails with a protocol error, incorrectly treating keyword list expressions in attributes as BitStrings.

Error message

mix format failed for file: lib/enaia_web/surface/forms/landlord_deal/steps/details_form.sface
** (Protocol.UndefinedError) protocol Enumerable not implemented for BitString. 

Got value:
    "[for: for_id]"

    (elixir 1.19.0-rc.0) lib/enum.ex:5: Enumerable.impl_for!/1
    (elixir 1.19.0-rc.0) lib/enum.ex:234: Enumerable.slice/1
    (elixir 1.19.0-rc.0) lib/enum.ex:4713: Enum.slice_count_and_fun/2
    (elixir 1.19.0-rc.0) lib/enum.ex:3031: Enum.slice_range/4
    (surface 0.12.1) lib/surface/formatter/phases/render.ex:451: Surface.Formatter.Phases.Render.format_attribute_expression/2
    (surface 0.12.1) lib/surface/formatter/phases/render.ex:374: Surface.Formatter.Phases.Render.render_attribute/2
    (elixir 1.19.0-rc.0) lib/enum.ex:1688: Enum."-map/2-lists^map/1-1-"/2

How to reproduce

1. Use Elixir 1.19.0-rc.0
2. Have Surface 0.12.1 in your project
3. Create a .sface file with a slot that uses :let with keyword list syntax:

   <:company_name_label :let={for: for_id}>
   

4. Run mix format

Root cause

The Surface formatter at lib/surface/formatter/phases/render.ex:451 (in format_attribute_expression/2) appears to be receiving keyword list expressions as strings (BitStrings) instead of proper AST structures when running under Elixir 1.19.0-rc.0.

Fix

PR #767 fixes this by using IO.iodata_to_binary and String.slice instead of Enum.slice.

Workaround

Temporarily disable the Surface.Formatter.Plugin in .formatter.exs:

plugins: [
  # Surface.Formatter.Plugin, # Temporarily disabled due to Elixir 1.19.0-rc.0 incompatibility
  Phoenix.LiveView.HTMLFormatter,
  # ... other plugins
]

Environment

• Surface: v0.12.1
• Elixir: v1.19.0-rc.0
• Phoenix LiveView: v1.0.0