core: SyncedFolders middleware saves what it synced

lib/vagrant/action/builtin/mixin_synced_folders.rb

@@ -62,7 +62,21 @@ module Vagrant
         #
         # @param [Machine] machine The machine that the folders belong to
         # @param [Hash] folders The result from a {#synced_folders} call.
-        def save_synced_folders(machine, folders)
+        def save_synced_folders(machine, folders, **opts)
+          if opts[:merge]
+            existing = cached_synced_folders(machine)
+            if existing
+              folders.each do |impl, fs|
+                existing[impl] ||= {}
+                fs.each do |id, data|
+                  existing[impl][id] = data
+                end
+              end
+
+              folders = existing
+            end
+          end
+
           machine.data_dir.join("synced_folders").open("w") do |f|
             f.write(JSON.dump(folders))
           end

lib/vagrant/action/builtin/synced_folders.rb

@@ -18,7 +18,12 @@ module Vagrant
         end
 
         def call(env)
-          folders = synced_folders(env[:machine], env[:synced_folders_config])
+          opts = {
+            cached: !!env[:synced_folders_cached],
+          }
+
+          folders = synced_folders(
+            env[:machine], env[:synced_folders_config], **opts)
 
           folders.each do |impl_name, fs|
             @logger.info("Synced Folder Implementation: #{impl_name}")
@@ -82,6 +87,9 @@ module Vagrant
             @logger.info("Invoking synced folder enable: #{impl_name}")
             impl.enable(env[:machine], fs, impl_opts(impl_name, env))
           end
+
+          # Save the synced folders
+          save_synced_folders(env[:machine], folders, merge: true)
         end
       end
     end

test/unit/vagrant/action/builtin/mixin_synced_folders_test.rb

@@ -158,5 +158,32 @@ describe Vagrant::Action::Builtin::MixinSyncedFolders do
       })
       expect(result[:nfs]).to eq({ "nfs" => old_folders["nfs"] })
     end
+
+    it "should be able to save and retrieve cached versions" do
+      folders["foo"] = { type: "default" }
+      result = subject.synced_folders(machine)
+      subject.save_synced_folders(machine, result)
+
+      # Clear the folders and set some more
+      folders.clear
+      folders["bar"] = { type: "default" }
+      folders["baz"] = { type: "nfs" }
+      result = subject.synced_folders(machine)
+      subject.save_synced_folders(machine, result, merge: true)
+
+      # Clear one last time
+      folders.clear
+
+      # Read them all back
+      result = subject.synced_folders(machine, nil, cached: true)
+      expect(result.length).to eq(2)
+      expect(result[:default]).to eq({
+        "foo" => { type: "default" },
+        "bar" => { type: "default" },
+      })
+      expect(result[:nfs]).to eq({
+        "baz" => { type: "nfs" }
+      })
+    end
   end
 end

test/unit/vagrant/action/builtin/synced_folders_test.rb

@@ -44,6 +44,7 @@ describe Vagrant::Action::Builtin::SyncedFolders do
       env[:root_path] = Pathname.new(Dir.mktmpdir)
       subject.stub(:plugins => plugins)
       subject.stub(:synced_folders => synced_folders)
+      allow(subject).to receive(:save_synced_folders)
     end
 
     it "should create on the host if specified" do
@@ -189,7 +190,7 @@ describe Vagrant::Action::Builtin::SyncedFolders do
       env[:synced_folders_config] = new_config
 
       expect(subject).to receive(:synced_folders).
-        with(machine, new_config).
+        with(machine, new_config, cached: false).
         and_return(synced_folders)
 
       subject.call(env)