Magic title helper for Rails: for FoosController#show, it uses `t(:"foos.show.title")` unless you do `<% self.title = "Something" %>` in the view.

layout.slim

html
  head
    title= title("My site")

title_helper.rb

 module TitleHelper
  def title=(title)
    @page_title = title
  end

  def title(base_title = nil)
    [page_title, base_title].compact.join(" – ")
  end

  private

  def page_title
    @page_title || default_page_title
  end

  def default_page_title
    # Reinventing t(:".foo") since this is called from a layout.
    key = (
      controller.controller_path.split("/") +
      [controller.action_name, "title"]
    ).join(".")
    t(key, default: "").presence
  end
end

I should spec and gemify this. I think I already have a gem from a previous implementation of something similar…

FIXME: if e.g. #create renders "new", this breaks