Only prepare 10 shares per command to prevent exceeding allowed command size

When a large number of shares are defined it may cause the generated
command to exceed the maximum allowed length. To prevent this, only
allow 10 shares to be processed at a time.

Fixes #10483

plugins/hosts/windows/cap/smb.rb

@@ -100,9 +100,14 @@ module VagrantPlugins
             ]
           end
           if !shares.empty?
+            uac_notified = false
+            shares.each_slice(10) do |s_shares|
+              if !uac_notified
                 machine.env.ui.warn("\n" + I18n.t("vagrant_sf_smb.uac.create_warning") + "\n")
+                uac_notified = true
                 sleep(UAC_PROMPT_WAIT)
-            result = Vagrant::Util::PowerShell.execute(script_path, *shares, sudo: true)
+              end
+              result = Vagrant::Util::PowerShell.execute(script_path, *s_shares, sudo: true)
               if result.exit_code != 0
                 share_path = result.stdout.to_s.sub("share path: ", "")
                 raise SyncedFolderSMB::Errors::DefineShareFailed,
@@ -112,6 +117,7 @@ module VagrantPlugins
               end
             end
           end
+        end
 
         # Generate a list of existing local smb shares
         #

test/unit/plugins/hosts/windows/cap/smb_test.rb

@@ -228,6 +228,18 @@ Remark     Not Vagrant Owned
         expect(machine.env.ui).not_to receive(:warn)
       end
     end
+
+    context "when more than 10 shares are defined" do
+      let(:folders) {
+        Hash[12.times.map{|i| ["/path#{i}", {hostpath: "/host#{i}"}]}]
+      }
+
+      after{ subject.smb_prepare(env, machine, folders, options) }
+
+      it "should execute multiple powershell commands" do
+        expect(Vagrant::Util::PowerShell).to receive(:execute).twice.with(any_args, sudo: true)
+      end
+    end
   end
 
   describe ".get_smbshares" do