Nice error message if port collisions are detected on `resume` [GH-602]

lib/vagrant/action.rb

@@ -29,6 +29,7 @@ module Vagrant
       autoload :CheckAccessible,     'vagrant/action/vm/check_accessible'
       autoload :CheckBox,            'vagrant/action/vm/check_box'
       autoload :CheckGuestAdditions, 'vagrant/action/vm/check_guest_additions'
+      autoload :CheckPortCollisions, 'vagrant/action/vm/check_port_collisions'
       autoload :CleanMachineFolder,  'vagrant/action/vm/clean_machine_folder'
       autoload :ClearForwardedPorts, 'vagrant/action/vm/clear_forwarded_ports'
       autoload :ClearNFSExports,     'vagrant/action/vm/clear_nfs_exports'

lib/vagrant/action/builtin.rb

@@ -59,6 +59,7 @@ module Vagrant
         Builder.new do
           use General::Validate
           use VM::CheckAccessible
+          use VM::CheckPortCollisions
           use VM::Resume
         end
       end

lib/vagrant/action/vm/check_port_collisions.rb

@@ -0,0 +1,26 @@
+module Vagrant
+  module Action
+    module VM
+      # Action that checks to make sure there are no forwarded port collisions,
+      # and raises an exception if there is.
+      class CheckPortCollisions
+        def initialize(app, env)
+          @app = app
+        end
+
+        def call(env)
+          existing = env[:vm].driver.read_used_ports
+
+          env[:vm].config.vm.forwarded_ports.each do |name, options|
+            if existing.include?(options[:hostport].to_i)
+              # We have a collision!
+              raise Errors::ForwardPortCollisionResume
+            end
+          end
+
+          @app.call(env)
+        end
+      end
+    end
+  end
+end

lib/vagrant/errors.rb

@@ -188,6 +188,11 @@ module Vagrant
       error_key(:collision_error, "vagrant.actions.vm.forward_ports")
     end
 
+    class ForwardPortCollisionResume < VagrantError
+      status_code(62)
+      error_key(:port_collision_resume)
+    end
+
     class MultiVMEnvironmentRequired < VagrantError
       status_code(5)
       error_key(:multi_vm_required)

templates/locales/en.yml

@@ -71,6 +71,12 @@ en:
       no_env: |-
         A Vagrant environment is required to run this command. Run `vagrant init`
         to set one up.
+      port_collision_resume: |-
+        This VM cannot be resumed, because the forwarded ports would collide with
+        another running virtual machine. Normally, Vagrant will attempt to fix this
+        for you but VirtualBox only allows forwarded ports to change if the VM is
+        powered off. Therefore, please reload your VM or halt the other running
+        VMs to continue.
       scp_unavailable: |-
         SSH server on the guest doesn't support SCP. Please install the necessary
         software to enable SCP on your guest operating system.