Fixes #9591: Allow for 'default' smb_username if set

Prior to this commit, Vagrant would prompt for smb username and password
every time, even if only smb_username was defined. This commit changes
that by allowing a "default" username from the Vagrantfile, with the
option of overriding it.

plugins/synced_folders/smb/synced_folder.rb

@@ -39,19 +39,27 @@ module VagrantPlugins
         # If we need auth information, then ask the user.
         have_auth = false
         folders.each do |id, data|
-          if data[:smb_username] && data[:smb_password]
-            smb_username = data[:smb_username]
-            smb_password = data[:smb_password]
+          smb_username = data[:smb_username] if data[:smb_username]
+          smb_password = data[:smb_password] if data[:smb_password]
+          if smb_username && smb_password
             have_auth = true
             break
           end
         end
 
+        modify_username = false
         if !have_auth
           machine.ui.detail(I18n.t("vagrant_sf_smb.warning_password") + "\n ")
           retries = 0
           while retries < CREDENTIAL_RETRY_MAX do
-            smb_username = machine.ui.ask("Username: ")
+            if smb_username
+              username = machine.ui.ask("Username (#{smb_username}): ")
+              smb_username = username if username != ""
+              modify_username = true
+            else
+              smb_username = machine.ui.ask("Username: ")
+            end
+
             smb_password = machine.ui.ask("Password (will be hidden): ", echo: false)
             auth_success = true
 
@@ -77,7 +85,12 @@ module VagrantPlugins
         end
 
         folders.each do |id, data|
-          data[:smb_username] ||= smb_username
+          if modify_username
+            # Only override original username if user requests to
+            data[:smb_username] = smb_username
+          else
+            data[:smb_username] ||= smb_username
+          end
           data[:smb_password] ||= smb_password
 
           # Register password as sensitive

test/unit/plugins/synced_folders/smb/synced_folder_test.rb

@@ -69,6 +69,36 @@ describe VagrantPlugins::SyncedFolderSMB::SyncedFolder do
   describe ".prepare" do
     let(:host_caps){ [:smb_start, :smb_prepare] }
 
+    context "with username credentials provided" do
+      let(:folders){ {'/first/path' => {smb_username: 'smbuser'}} }
+
+      it "should prompt for credentials" do
+        expect(machine.env.ui).to receive(:ask).with(/name/, any_args).and_return('username').at_least(1)
+        expect(machine.env.ui).to receive(:ask).with(/word/, any_args).and_return('password').at_least(1)
+
+        subject.prepare(machine, folders, options)
+      end
+
+      it "should set credential information into all folder options and override username" do
+        expect(machine.env.ui).to receive(:ask).with(/name/, any_args).and_return('username').at_least(1)
+        expect(machine.env.ui).to receive(:ask).with(/word/, any_args).and_return('password').at_least(1)
+
+        subject.prepare(machine, folders, options)
+        expect(folders['/first/path'][:smb_username]).to eq('username')
+        expect(folders['/first/path'][:smb_password]).to eq('password')
+      end
+
+
+      it "will use configured default with no input" do
+        expect(machine.env.ui).to receive(:ask).with(/name/, any_args).and_return('').at_least(1)
+        expect(machine.env.ui).to receive(:ask).with(/word/, any_args).and_return('password').at_least(1)
+
+        subject.prepare(machine, folders, options)
+        expect(folders['/first/path'][:smb_username]).to eq('smbuser')
+        expect(folders['/first/path'][:smb_password]).to eq('password')
+      end
+    end
+
     context "without credentials provided" do
       before do
         expect(machine.env.ui).to receive(:ask).with(/name/, any_args).and_return('username').at_least(1)