Reverse dependency tree.

- `stop` uses it to stop services that depend upon something that has
    to be stopped.

src/main.cr

@@ -195,6 +195,14 @@ class Service
 		}.to_yaml
 	end
 
+	def id
+		if @environment.name == "root"
+			name
+		else
+			"#{@environment.name}/#{name}"
+		end
+	end
+
 	# FIXME: At this point, macros would be both more readable and shorter.
 	def name
 		@reference.name
@@ -340,13 +348,16 @@ class Service
 			service.name == service_name
 		end
 	end
+	def is_id?(id)
+		id == self.id || (@environment.name == "root" && id == "root/#{name}")
+	end
 
-	alias DependencyTree = Array(DependencyTree) | Service
+	alias ServiceTree = Array(ServiceTree) | Service
 
 	# Returns a dependency tree.
 	# You’ll probably want to flatten and reverse it afterwards.
 	def dependency_tree
-		tree = [self] of DependencyTree
+		tree = [self] of ServiceTree
 
 		@consumes.each do |token|
 			service = Service.get_by_id token.from
@@ -362,6 +373,20 @@ class Service
 
 		tree
 	end
+
+	def reverse_dependency_tree
+		tree = [self] of ServiceTree
+
+		@@all.each do |service|
+			service.providers.any? do |token, id|
+				if self.is_id?(id) && ! tree.any? service
+					tree << service
+				end
+			end
+		end
+
+		tree
+	end
 end
 
 args = [] of String
@@ -442,8 +467,13 @@ begin
 		services.each do |service|
 			# FIXME: Build revdep tree and stop services started as dependencies?
 			if service.status(PID_DIRECTORY) == Service::Status::Running
-				puts "stopping #{service.to_s}"
+				# FIXME: Should we remove duplicate services from the
-				service.stop PID_DIRECTORY
+				#        tree once flattened?
+				service.reverse_dependency_tree.flatten.reverse.each do |service|
+
+					puts "stopping #{service.to_s}"
+					service.stop PID_DIRECTORY
+				end
 			end
 		end
 	elsif args[0] == "status"