Add a --list-plugins hook

hooks/boot/05-plugins.rb

@@ -0,0 +1 @@
+app_option('--list-plugins', :flag, "List all available plugins")

hooks/pre_validations/05-plugins.rb

@@ -0,0 +1,87 @@
+if app_value(:list_plugins)
+
+  class Plugin
+    include Comparable
+
+    attr_reader :group, :plugin, :provider, :module
+
+    # We expect a mymod::plugin::myplugin structure but also allow
+    # mymod::plugin::myplugin::provider
+    def initialize(mod)
+      parts = mod.identifier.split('::')
+
+      raise ArgumentError, "#{mod.identifier} is not a plugin" unless parts.length >= 3
+
+      type = ['plugin', 'cli', 'compute'].detect { |type| parts.include?(type) }
+      raise ArgumentError, "#{mod.identifier} is not a plugin" unless type
+
+      index = parts.index(type)
+      if type == 'plugin'
+        @group = parts.slice(0, index).join(' ')
+      else
+        @group = parts.slice(0, index + 1).join(' ')
+      end
+      @plugin, @provider = parts.slice(index + 1, parts.length)
+
+      @module = mod
+    end
+
+    def name
+      provider || plugin
+    end
+
+    def to_s
+      mod.identifier
+    end
+
+    def inspect
+      "<Plugin:#{mod.identifier}>"
+    end
+
+    def <=>(other)
+      if group != other.group
+        group <=> other.group
+      elsif plugin != other.plugin
+        plugin <=> other.plugin
+      elsif provider
+        if other.provider
+          provider <=> other.provider
+        else
+          1
+        end
+      elsif other.provider
+        -1
+      else
+        0
+      end
+    end
+  end
+
+  groups = Hash.new { |h, k| h[k] = [] }
+
+  kafo.modules.each do |mod|
+    begin
+      plugin = Plugin.new(mod)
+      groups[plugin.group] << plugin
+    rescue ArgumentError
+    end
+  end
+
+  if groups.any?
+    groups.each do |group, plugins|
+      say "* #{group.tr('_', ' ').capitalize}"
+      plugins.sort.each do |plugin|
+        enabled = plugin.module.enabled? ? 'enabled' : 'disabled'
+        indenting = plugin.provider ? '    ' : '  '
+
+        # TODO: assumes there is a plugin but breaks with
+        # foreman_proxy::plugin::dns::powerdns because dns is built in
+        say "#{indenting}* #{plugin.name} (#{enabled})"
+      end
+    end
+  else
+    say "No plugins available in #{scenario_data.name}"
+  end
+
+  exit(0)
+end