Behaviour for transforming HEEx tokens before they are processed by TagEngine.

This allows compile-time modification of the parsed template structure, enabling injection of attributes into tags and components.

Token Structure

Tokens from Phoenix.LiveView.Tokenizer include:

• {:tag, name, attrs, meta} - HTML elements like <div>, <input>
• {:remote_component, name, attrs, meta} - Components like <Foo.bar>
• {:local_component, name, attrs, meta} - Components like <.foo>
• {:slot, name, attrs, meta} - Slots like <:header>
• {:close, type, name, meta} - Closing tags
• {:text, content, meta} - Text content
• {:expr, marker, content} - Elixir expressions {...}

Attributes are tuples of {name, value, meta} where value is:

• {:string, content, meta} - String literal "foo"
• {:expr, content, meta} - Expression {@foo}
• nil - Boolean attribute

Example

defmodule MyTransformer do
  @behaviour Lavash.TokenTransformer

  @impl true
  def transform(tokens, state) do
    Enum.map(tokens, fn
      {:tag, "input", attrs, meta} ->
        # Inject a data attribute
        new_attr = {"data-my-attr", {:string, "value", meta}, meta}
        {:tag, "input", [new_attr | attrs], meta}

      token ->
        token
    end)
  end
end