visualize_rake_tasks.rb

## There are dependencies we cannot see, e.g. when a task
## invokes another one programmatically

# find all tasks for which we provide an action
tasks1 = Rake.application.tasks.select { |task|
  task.actions.any?
}.reject { |task|
  task.actions.first.source_location.first["/gems"]
}

# add those that depend on a task in task1
# (not a transitive closure)
tasks2 = Rake.application.tasks.select { |task|
  tasks1.include?(task) || (task.prerequisites & tasks1.map(&:name)).any?
}

TaskData = Struct.new(:task, :dependent_count, :children, :inline, :full, :display) do
  def render_independently?
    !(dependent_count == 1 && children.length < 2)
  end 
end

data = tasks2.each_with_object({}) { |task, hash|
  hash[task.name] = TaskData.new(task, 0)
}

tasks2.each do |task|
  task.prerequisites.each do |dep|
    data[dep].dependent_count += 1
  end 
  data[task.name].children = task.prerequisites.map { |name| data[name] }
end

data.values.each do |td|
  if td.children.none?
    td.inline = td.full = td.task.name
    td.display = td.task.name
  elsif td.render_independently?
    td.inline = td.task.name
  end 
end

data.length.times do
  data.values.each do |td|
    if td.children.all?(&:inline)
      td.full = "#{td.task.name} => [#{td.children.map(&:inline).join ", "}]"
      td.inline ||= td.full
    end 
  end 
end

data.values
  .select(&:render_independently?)
  .each do |td|
    puts td.full
  end