User.follow_all: ensure its stays unique

lib/pleroma/user.ex

@@ -315,7 +315,16 @@ def follow_all(follower, followeds) do
     q =
       from(u in User,
         where: u.id == ^follower.id,
-        update: [set: [following: fragment("array_cat(?, ?)", u.following, ^followed_addresses)]]
+        update: [
+          set: [
+            following:
+              fragment(
+                "array(select distinct unnest (array_cat(?, ?)))",
+                u.following,
+                ^followed_addresses
+              )
+          ]
+        ]
       )
 
     {1, [follower]} = Repo.update_all(q, [], returning: true)

test/user_test.exs

@@ -65,6 +65,19 @@ test "follow_all follows mutliple users" do
     refute User.following?(user, not_followed)
   end
 
+  test "follow_all follows mutliple users without duplicating" do
+    user = insert(:user)
+    followed_zero = insert(:user)
+    followed_one = insert(:user)
+    followed_two = insert(:user)
+
+    {:ok, user} = User.follow_all(user, [followed_zero, followed_one])
+    assert length(user.following) == 3
+
+    {:ok, user} = User.follow_all(user, [followed_one, followed_two])
+    assert length(user.following) == 4
+  end
+
   test "follow takes a user and another user" do
     user = insert(:user)
     followed = insert(:user)