Fix voters count field

Mastodon API demands this be null unless it’s a multi-selection poll.
Not abiding by this can mess up display in some clients.

Fixes: AkkomaGang/akkoma#190

CHANGELOG.md

@@ -18,6 +18,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## Fixed
 - Meilisearch: order of results returned from our REST API now actually matches how Meilisearch ranks results
 - AP objects with additional JSON-LD profiles beyond ActivityStreams can now be fetched
+- Single-selection polls no longer expose the voter_count; MastoAPI demands it be null
+  and this confused some clients leading to vote distributions >100%
 
 ## Changed
 - Refactored Rich Media to cache the content in the database. Fetching operations that could block status rendering have been eliminated.

lib/pleroma/web/api_spec/schemas/poll.ex

@@ -32,7 +32,9 @@ defmodule Pleroma.Web.ApiSpec.Schemas.Poll do
       },
       voters_count: %Schema{
         type: :integer,
-        description: "How many unique accounts have voted. Number."
+        nullable: true,
+        description:
+          "How many unique accounts have voted for a multi-selection poll. Number, or null if single-selection poll."
       },
       voted: %Schema{
         type: :boolean,

lib/pleroma/web/mastodon_api/views/poll_view.ex

@@ -19,7 +19,7 @@ def render("show.json", %{object: object, multiple: multiple, options: options}
       expired: expired,
       multiple: multiple,
       votes_count: votes_count,
-      voters_count: voters_count(object),
+      voters_count: voters_count(multiple, object),
       options: options,
       emojis: Pleroma.Web.MastodonAPI.StatusView.build_emojis(object.data["emoji"])
     }
@@ -68,11 +68,19 @@ defp options_and_votes_count(options) do
     end)
   end
 
-  defp voters_count(%{data: %{"voters" => voters}}) when is_list(voters) do
+  defp voters_count(false, _poll_data) do
+    # Mastodon always sets voter count to "null" unless multiple options were selectable
+    # Some clients may rely on this to detect multiple selection polls and it can mess
+    # up percentages for some clients if we never got a correct remote voter count and
+    # only count local voters here; see https://akkoma.dev/AkkomaGang/akkoma/issues/190
+    nil
+  end
+
+  defp voters_count(_multiple, %{data: %{"voters" => voters}}) when is_list(voters) do
     length(voters)
   end
 
-  defp voters_count(_), do: 0
+  defp voters_count(_, _), do: 0
 
   defp voted_and_own_votes(%{object: object} = params, options) do
     if params[:for] do

test/pleroma/web/mastodon_api/views/poll_view_test.exs

@@ -43,7 +43,7 @@ test "renders a poll" do
         %{title: "why are you even asking?", votes_count: 0}
       ],
       votes_count: 0,
-      voters_count: 0
+      voters_count: nil
     }
 
     result = PollView.render("show.json", %{object: object})