providers/docker: warning if synced folders change

plugins/providers/docker/action.rb

@@ -213,7 +213,6 @@ module VagrantPlugins
             b2.use HostMachineSyncFolders
             b2.use PrepareNFSValidIds
             b2.use SyncedFolderCleanup
-            b2.use SyncedFolders
             b2.use PrepareNFSSettings
 
             # If the VM is NOT created yet, then do some setup steps
@@ -221,12 +220,14 @@ module VagrantPlugins
             b2.use Call, IsState, :not_created do |env2, b3|
               if env2[:result]
                 b3.use EnvSet, port_collision_repair: true
-                b3.use HostMachineSyncFolders
                 b3.use HostMachinePortWarning
                 b3.use HostMachinePortChecker
                 b3.use HandleForwardedPortCollisions
+                b3.use SyncedFolders
                 b3.use Create
                 b3.use WaitForRunning
+              else
+                b3.use CompareSyncedFolders
               end
             end
 
@@ -244,6 +245,7 @@ module VagrantPlugins
 
       # The autoload farm
       action_root = Pathname.new(File.expand_path("../action", __FILE__))
+      autoload :CompareSyncedFolders, action_root.join("compare_synced_folders")
       autoload :Create, action_root.join("create")
       autoload :Destroy, action_root.join("destroy")
       autoload :HasSSH, action_root.join("has_ssh")

plugins/providers/docker/action/compare_synced_folders.rb

@@ -0,0 +1,58 @@
+require "vagrant/action/builtin/mixin_synced_folders"
+
+module VagrantPlugins
+  module DockerProvider
+    module Action
+      class CompareSyncedFolders
+        include Vagrant::Action::Builtin::MixinSyncedFolders
+
+        def initialize(app, env)
+          @app = app
+        end
+
+        def call(env)
+          machine = env[:machine]
+
+          # Get the synced folders that are cached, and those that aren't
+          cached = synced_folders(machine, cached: true)
+          fresh  = synced_folders(machine)
+
+          # Build up a mapping of existing setup synced folders
+          existing = {}
+          cached.each do |_, fs|
+            fs.each do |_, data|
+              existing[data[:guestpath]] = data[:hostpath]
+            end
+          end
+
+          # Remove the matching folders, and build up non-matching or
+          # new syncedf olders.
+          invalids = {}
+          fresh.each do |_, fs|
+            fs.each do |_, data|
+              invalid = false
+              old     = existing.delete(data[:guestpath])
+              invalid = true if !old
+
+              if !invalid && old
+                invalid = true if old != data[:hostpath]
+              end
+
+              if invalid
+                invalids[data[:guestpath]] = data[:hostpath]
+              end
+            end
+          end
+
+          # If we have invalid entries, these are changed or new entries.
+          # If we have existing entries, then we removed some entries.
+          if !invalids.empty? || !existing.empty?
+            machine.ui.warn(I18n.t("docker_provider.synced_folders_changed"))
+          end
+
+          @app.call(env)
+        end
+      end
+    end
+  end
+end

templates/locales/providers_docker.yml

@@ -32,6 +32,10 @@ en:
     ssh_through_host_vm: |-
       SSH will be proxied through the Docker virtual machine since we're
       not running Docker natively. This is just a notice, and not an error.
+    synced_folders_changed: |-
+      Vagrant has noticed that the synced folder definitions have changed.
+      With Docker, these synced folder changes won't take effect until you
+      destroy the container and recreate it.
     waiting_for_running: |-
       Waiting for container to enter "running" state...