[GH-6] Error out if multiple provider specific cache dirs are found and prepare to move dirs around in case a single cache dir exists

lib/vagrant-cachier/action/ensure_single_cache_root.rb

@@ -1,3 +1,5 @@
+require_relative '../errors'
+
 module VagrantPlugins
   module Cachier
     class Action
@@ -7,9 +9,51 @@ module VagrantPlugins
         end
 
         def call(env)
-          raise 'Do our work'
+          @env = env
+
+          # If the cache is scoped to boxes or the existing cache dirs are not
+          # provider specific, there's nothing we need to do
+          if cache_scoped_to_machine? && provider_specific_cache_dirs.any?
+            ensure_single_cache_root_exists!
+          end
+
           @app.call(env)
         end
+
+        def cache_scoped_to_machine?
+          @env[:machine].config.cache.scope.to_sym == :machine
+        end
+
+        def ensure_single_cache_root_exists!
+          if provider_specific_cache_dirs.size > 1
+            cache_dirs = provider_specific_cache_dirs.map do |dir|
+              "  - #{dir.to_s.gsub(/^#{@env[:root_path]}\//, '')}"
+            end
+            machine_path = @env[:machine].data_dir.parent.to_s.gsub(/^#{@env[:root_path]}\//, '')
+            raise Cachier::Errors::MultipleProviderSpecificCacheDirsFound,
+                      machine:      @env[:machine].name,
+                      machine_path: machine_path,
+                      dirs:         cache_dirs.join("\n")
+          else
+            current_path = provider_specific_cache_dirs.first.to_s.gsub(/^#{@env[:root_path]}\//, '')
+            new_path     = @env[:machine].data_dir.parent.join('cache').to_s.gsub(/^#{@env[:root_path]}\//, '')
+            # If we got here there is a single provider specific cacher dir, so
+            # let's be nice with users and just fix it ;)
+            @env[:ui].warn I18n.t('vagrant_cachier.will_fix_machine_cache_dir',
+                                  current_path: current_path,
+                                  new_path:     new_path)
+            raise 'Move cache dir around'
+          end
+        end
+
+        def provider_specific_cache_dirs
+          return @provider_specific_cache_dirs if @provider_specific_cache_dirs
+
+          # By default data_dir points to ./.vagrant/machines/<NAME>/<PROVIDER>,
+          # so we go one directory up
+          machine_dir = @env[:machine].data_dir.parent
+          @provider_specific_cache_dirs = Pathname.glob(machine_dir.join('*/cache'))
+        end
       end
     end
   end

lib/vagrant-cachier/errors.rb

@@ -0,0 +1,9 @@
+module VagrantPlugins
+  module Cachier
+    module Errors
+      class MultipleProviderSpecificCacheDirsFound < Vagrant::Errors::VagrantError
+        error_key(:multiple_provider_specific_cache_dirs_found)
+      end
+    end
+  end
+end

lib/vagrant-cachier/plugin.rb

@@ -50,12 +50,12 @@ module VagrantPlugins
       #       possible provider action class that Vagrant might have
       ensure_single_cache_root = lambda do |hook|
         require_relative 'action/ensure_single_cache_root'
-        hook.after VagrantPlugins::ProviderVirtualBox::Action::Boot, Action::EnsureSingleCacheRoot
+        hook.before VagrantPlugins::ProviderVirtualBox::Action::Boot, Action::EnsureSingleCacheRoot
 
         if defined?(Vagrant::LXC)
           # TODO: Require just the boot action file once its "require dependencies" are sorted out
           require 'vagrant-lxc/action'
-          hook.after Vagrant::LXC::Action::Boot, Action::EnsureSingleCacheRoot
+          hook.before Vagrant::LXC::Action::Boot, Action::EnsureSingleCacheRoot
         end
       end
       action_hook 'ensure-single-cache-root-exists-on-up',     :machine_action_up,     &ensure_single_cache_root

lib/vagrant-cachier/provision_ext.rb

@@ -56,7 +56,7 @@ module VagrantPlugins
               when :box
                 @env[:home_path].join('cache', @env[:machine].box.name)
               when :machine
-                @env[:machine].data_dir.join('cache')
+                @env[:machine].data_dir.parent.join('cache')
               else
                 raise "Unknown cache scope: '#{@env[:machine].config.cache.scope}'"
             end

locales/en.yml

@@ -6,3 +6,15 @@ en:
       Skipping %{bucket} cache bucket as the guest machine does not support it
     unknown_cache_scope: |-
       Unknown cache scope '%{cache_scope}' (allowed scopes: %{allowed})
+    will_fix_machine_cache_dir: |-
+      A vagrant-cachier provider specific cache dir was found under
+      '%{current_path}' and it will be
+      moved to '%{new_path}' as it is the new path for keeping machine
+      scoped cache dirs starting with the 0.3.0 version of the plugin.
+  vagrant:
+    errors:
+      multiple_provider_specific_cache_dirs_found: |-
+        There are multiple provider specific cache dirs for the '%{machine}' machine:
+        %{dirs}
+        Please move one of them up to `%{machine_path}/cache` and remove the others
+        before bringing the machine up again.