Add tool to visualize Jobs in graphviz dot format

app/models/job/state_machine.rb

@@ -1,6 +1,20 @@
 module Job::StateMachine
   extend ActiveSupport::Concern
 
+  module ClassMethods
+    #
+    # Helper methods for display of transitions
+    #
+
+    def to_dot(*args)
+      new.to_dot(*args)
+    end
+
+    def to_svg(*args)
+      new.to_svg(*args)
+    end
+  end
+
   def transitions
     @transitions ||= load_transitions
   end
@@ -51,4 +65,35 @@ def queue_signal(*args, priority: MiqQueue::NORMAL_PRIORITY, role: nil, deliver_
       :server_guid => server_guid
     )
   end
+
+  #
+  # Helper methods for display of transitions
+  #
+
+  def to_dot(include_starred_states = false)
+    all_states = transitions.values.map(&:to_a).flatten.uniq.reject { |t| t == "*" }
+
+    "".tap do |s|
+      s << "digraph #{self.class.name.inspect} {\n"
+      transitions.each do |signal, signal_transitions|
+        signal_transitions.each do |from, to|
+          next if !include_starred_states && (from == "*" || to == "*")
+
+          from = from == "*" ? all_states : [from]
+          to   = to == "*"   ? all_states : [to]
+          from.product(to).each { |f, t| s << "  #{f} -> #{t} [ label=\"#{signal}\" ]\n" }
+        end
+      end
+      s << "}\n"
+    end
+  end
+
+  def to_svg(include_starred_states = false)
+    require "open3"
+    out, err, _status = Open3.capture3("dot -Tsvg", :stdin_data => to_dot(include_starred_states))
+
+    raise "Error from graphviz:\n#{err}" if err.present?
+
+    out
+  end
 end

tools/job_to_svg.rb

@@ -0,0 +1,21 @@
+#!/usr/bin/env ruby
+
+if ARGV.empty?
+  puts "USAGE: #{__FILE__} job_class [outfile]"
+  exit 1
+end
+
+job_class, outfile = ARGV
+
+require File.expand_path("../config/environment", __dir__)
+
+job_class = job_class.constantize rescue NilClass
+unless job_class < Job
+  puts "ERROR: job_class is not a subclass of Job.\n\nValid job_class values are:"
+  puts Job.descendants.map(&:name).sort.join("\n").indent(2)
+  exit 1
+end
+
+outfile ||= "#{job_class.name.underscore.tr("/", "-")}.svg"
+File.write(outfile, job_class.to_svg)
+puts "\nWritten to #{outfile}"