Only write box metadata if guest has box object

Prior to this commit, providers like docker would fail to be brought up
because they do not store box objects like virtualbox or vmware
provider guests. This commit fixes that by making sure the box object
exists before writing the metadata file to disk.

plugins/commands/up/middleware/store_box_metadata.rb

@@ -10,19 +10,25 @@ module VagrantPlugins
     class StoreBoxMetadata
       def initialize(app, env)
         @app = app
+        @logger = Log4r::Logger.new("vagrant::up::storeboxmetadata")
       end
 
       def call(env)
-        box = env[:machine].box
-        box_meta = {
-          name: box.name,
-          version: box.version,
-          provider: box.provider,
-          directory: box.directory.sub(Vagrant.user_data_path.to_s + "/", "")
-        }
-        meta_file = env[:machine].data_dir.join("box_meta")
-        File.open(meta_file.to_s, "w+") do |file|
-          file.write(JSON.dump(box_meta))
+        if env[:machine].box
+          box = env[:machine].box
+          box_meta = {
+            name: box.name,
+            version: box.version,
+            provider: box.provider,
+            directory: box.directory.sub(Vagrant.user_data_path.to_s + "/", "")
+          }
+          meta_file = env[:machine].data_dir.join("box_meta")
+          @logger.debug("Writing box metadata file to #{meta_file}")
+          File.open(meta_file.to_s, "w+") do |file|
+            file.write(JSON.dump(box_meta))
+          end
+        else
+          @logger.debug("No box data found for #{env[:machine].name} with provider #{env[:machine].provider_name}")
         end
         @app.call(env)
       end

test/unit/plugins/commands/up/middleware/store_box_metadata_test.rb

@@ -26,6 +26,21 @@ describe VagrantPlugins::CommandUp::StoreBoxMetadata do
   let(:subject) { described_class.new(app, env) }
 
   describe "#call" do
+    context "with no box file" do
+      let(:machine) { double("machine", name: "guest", provider_name: "provider") }
+      let(:env) { {machine: machine} }
+
+      before do
+        allow(machine).to receive(:box).and_return(nil)
+        expect(app).to receive(:call).with(env)
+      end
+
+
+      it "does not write the metadata file" do
+        expect(File).to_not receive(:open)
+        subject.call(env)
+      end
+    end
 
     let(:meta_file) { double("meta_file") }