Destroy unused network interfaces on VM destroy

lib/vagrant/actions/vm/down.rb

@@ -6,6 +6,7 @@ module Vagrant
           # The true as the 2nd parameter always forces the shutdown so its
           # fast (since we're destroying anyways)
           @runner.add_action(Halt, :force => true) if @runner.vm.running?
+          @runner.add_action(Network)
           @runner.add_action(Destroy)
         end
 

lib/vagrant/actions/vm/network.rb

@@ -2,6 +2,25 @@ module Vagrant
   module Actions
     module VM
       class Network < Base
+        def before_destroy
+          # We need to check if the host only network specified by any
+          # of the adapters would not have any more clients if it was
+          # destroyed. And if so, then destroy the host only network
+          # itself.
+          interfaces = runner.vm.network_adapters.collect do |adapter|
+            adapter.host_interface_object
+          end
+
+          interfaces.compact.uniq.each do |interface|
+            # Destroy the network interface if there is only one
+            # attached VM (which must be this VM)
+            if interface.attached_vms.length == 1
+              logger.info "Destroying unused network interface..."
+              interface.destroy
+            end
+          end
+        end
+
         def before_boot
           assign_network if enable_network?
         end

test/vagrant/actions/vm/down_test.rb

@@ -19,13 +19,13 @@ class DownActionTest < Test::Unit::TestCase
     end
 
     should "add the destroy action alone if VM is not running" do
-      setup_action_expectations([Vagrant::Actions::VM::Destroy])
+      setup_action_expectations([Vagrant::Actions::VM::Network, Vagrant::Actions::VM::Destroy])
       @action.prepare
     end
 
     should "add the halt action if the VM is running" do
       @vm.expects(:running?).returns(true)
-      setup_action_expectations([[Vagrant::Actions::VM::Halt, {:force => true}], Vagrant::Actions::VM::Destroy])
+      setup_action_expectations([[Vagrant::Actions::VM::Halt, {:force => true}], Vagrant::Actions::VM::Network, Vagrant::Actions::VM::Destroy])
       @action.prepare
     end
   end

test/vagrant/actions/vm/network_test.rb

@@ -6,6 +6,35 @@ class NetworkTest < Test::Unit::TestCase
     @runner.stubs(:system).returns(linux_system(@vm))
   end
 
+  context "before destroy" do
+    setup do
+      @network_adapters = []
+      @vm.stubs(:network_adapters).returns(@network_adapters)
+    end
+
+    def stub_interface(length=5)
+      interface = mock("interface")
+      adapter = mock("adapter")
+      adapter.stubs(:host_interface_object).returns(interface)
+      interface.stubs(:attached_vms).returns(Array.new(length))
+
+      @network_adapters << adapter
+      interface
+    end
+
+    should "destroy only the unused network interfaces" do
+      stub_interface(5)
+      stub_interface(7)
+      results = [stub_interface(1), stub_interface(1)]
+
+      results.each do |result|
+        result.expects(:destroy).once
+      end
+
+      @action.before_destroy
+    end
+  end
+
   context "before boot" do
     setup do
       @action.stubs(:enable_network?).returns(false)