Phlex handler

phlex_template_handler.rb

# config/initializers/phlex_template_handler.rb
require "action_view"
require "phlex"

# Intercept unknown "capitalized" method calls (e.g., PageView(...)) in templates,
# look up a Phlex component class, instantiate it, and render it.
# Crucially, we re-bind the user’s block so that `self` is the component, not the ActionView context.
module PhlexDynamicMethodCalls
  def method_missing(name, *args, **kwargs, &block)
    # Only intercept method calls starting with an uppercase letter (e.g. "PageView", "MyComponent", etc.)
    if name[0] == name[0].upcase && Object.const_defined?(name)
      klass = Object.const_get(name)

      # If the constant is a Phlex component
      if klass < Phlex::HTML
        component = klass.new(*args, **kwargs)

        # We need to ensure the user's block is evaluated in the context of `component`,
        # rather than in the ActionView context. By default, `render_in` will capture
        # the block using Rails helpers, which is not what we want.
        #
        # Instead, we wrap the block in a small "re-bound" block that calls
        # `component.instance_exec(*yielded_args, &original_block)`.
        # That way, inside the block, `self == component`, so methods like `h1`, `p`, etc. work.
        if block
          return component.render_in(self) do |*yielded_args|
            # Evaluate the original block inside the component's context:
            component.instance_exec(*yielded_args, &block)
          end
        else
          # No block given
          return component.render_in(self)
        end
      end
    end

    # Otherwise, pass it up the chain
    super
  end

  def respond_to_missing?(name, include_private = false)
    if name[0] == name[0].upcase &&
       Object.const_defined?(name) &&
       Object.const_get(name) < Phlex::HTML
      true
    else
      super
    end
  end
end

class PhlexMethodMissingHandler
  def self.call(template, source)
    # We return Ruby code that extends the template's context with our method_missing module,
    # then runs the original source code from the .html.rb file.
    <<~RUBY
      extend ::PhlexDynamicMethodCalls
      #{source}
    RUBY
  end
end

# Tell Rails that ".html.rb" templates should use this custom handler:
ActionView::Template.register_template_handler :rb, PhlexMethodMissingHandler

view.html.rb

PageView(
  title: "This is a page"
){
   erb <<~ERB
    <h1><%= @title %></h1>
    <p>Why would somebody want to put ERB in their Phlex view? Who knows</p>
  ERB
  div(class: "prose prose-md"){
    markdown <<~MD
      * This
      * could
      * be
      * cool
    MD
  }
}