Fix Elixir 1.19.0-rc.0 formatter compatibility

[neilberkman]

Description

Fixes Surface formatter compatibility with Elixir 1.19.0-rc.0 while maintaining backward compatibility with Elixir 1.18.

Problem

When running mix format on .sface files with Elixir 1.19.0-rc.0, the Surface formatter crashes with:

** (Protocol.UndefinedError) protocol Enumerable not implemented for BitString

Got value:
    "[for: for_id]"

    (surface 0.12.1) lib/surface/formatter/phases/render.ex:451

Root Cause

In lib/surface/formatter/phases/render.ex, the formatter tries to use Enum.slice on the result of Code.format_string!, which returns iodata (not a list). Elixir 1.19 is stricter about this type mismatch.

Solution

Changed from:

|> Code.format_string!(locals_without_parens: [...: 1])
|> Enum.slice(1..-2//1)
|> to_string()

To:

|> Code.format_string!(locals_without_parens: [...: 1])
|> IO.iodata_to_binary()
|> String.slice(1..-2//1)

Also removed the redundant to_string() call in the else branch since IO.iodata_to_binary() already returns a binary.

Compatibility

This fix is fully backward compatible with Elixir 1.18:

• IO.iodata_to_binary/1 exists in both Elixir 1.18 and 1.19
• String.slice/2 exists in both versions
• Both return the same result as the original code

Testing

Tested formatting Surface templates with:

• Elixir 1.18.x
• Elixir 1.19.0-rc.0

Fixes #766