User: Don't allow local users in remote changesets

lib/pleroma/user.ex

@@ -472,7 +472,20 @@ def remote_user_changeset(struct \\ %User{local: false}, params) do
     |> validate_format(:nickname, @email_regex)
     |> validate_length(:bio, max: bio_limit)
     |> validate_length(:name, max: name_limit)
+    |> validate_inclusion(:local, [true])
     |> validate_fields(true)
+    |> validate_non_local()
+  end
+
+  defp validate_non_local(cng) do
+    local? = get_field(cng, :local)
+
+    if local? do
+      cng
+      |> add_error(:local, "User is local, can't update with this changeset.")
+    else
+      cng
+    end
   end
 
   def update_changeset(struct, params \\ %{}) do

test/pleroma/user_test.exs

@@ -895,6 +895,13 @@ test "it has required fields" do
         refute cs.valid?
       end)
     end
+
+    test "it is invalid given a local user" do
+      user = insert(:user)
+      cs = User.remote_user_changeset(user, %{name: "tom from myspace"})
+
+      refute cs.valid?
+    end
   end
 
   describe "followers and friends" do