Fix empty home feed before first follow has finished processing (#16152)

Change queue of merge worker from pull to default

app/models/concerns/account_interactions.rb

@@ -184,6 +184,14 @@ module AccountInteractions
     active_relationships.where(target_account: other_account).exists?
   end
 
+  def following_anyone?
+    active_relationships.exists?
+  end
+
+  def not_following_anyone?
+    !following_anyone?
+  end
+
   def blocking?(other_account)
     block_relationships.where(target_account: other_account).exists?
   end

app/models/user.rb

@@ -458,9 +458,7 @@ class User < ApplicationRecord
   end
 
   def regenerate_feed!
-    return unless Redis.current.setnx("account:#{account_id}:regeneration", true)
-    Redis.current.expire("account:#{account_id}:regeneration", 1.day.seconds)
-    RegenerationWorker.perform_async(account_id)
+    RegenerationWorker.perform_async(account_id) if Redis.current.set("account:#{account_id}:regeneration", true, nx: true, ex: 1.day.seconds)
   end
 
   def needs_feed_update?

app/services/follow_service.rb

@@ -30,6 +30,11 @@ class FollowService < BaseService
 
     ActivityTracker.increment('activity:interactions')
 
+    # When an account follows someone for the first time, avoid showing
+    # an empty home feed while the follow request is being processed
+    # and the feeds are being merged
+    mark_home_feed_as_partial! if @source_account.not_following_anyone?
+
     if (@target_account.locked? && !@options[:bypass_locked]) || @source_account.silenced? || @target_account.activitypub?
       request_follow!
     elsif @target_account.local?
@@ -39,6 +44,10 @@ class FollowService < BaseService
 
   private
 
+  def mark_home_feed_as_partial!
+    redis.set("account:#{@source_account.id}:regeneration", true, nx: true, ex: 1.day.seconds)
+  end
+
   def following_not_possible?
     @target_account.nil? || @target_account.id == @source_account.id || @target_account.suspended?
   end

app/workers/merge_worker.rb

@@ -3,11 +3,11 @@
 class MergeWorker
   include Sidekiq::Worker
 
-  sidekiq_options queue: 'pull'
-
   def perform(from_account_id, into_account_id)
     FeedManager.instance.merge_into_home(Account.find(from_account_id), Account.find(into_account_id))
   rescue ActiveRecord::RecordNotFound
     true
+  ensure
+    Redis.current.del("account:#{into_account_id}:regeneration")
   end
 end