Bump redis to 4.2.0.

lib/admin_confirmation.rb

@@ -43,7 +43,7 @@ class AdminConfirmation
   end
 
   def self.exists_for?(user_id)
-    Discourse.redis.exists "admin-confirmation:#{user_id}"
+    Discourse.redis.exists? "admin-confirmation:#{user_id}"
   end
 
   def self.find_by_code(token)

lib/discourse.rb

@@ -489,7 +489,7 @@ module Discourse
   end
 
   def self.readonly_mode?(keys = READONLY_KEYS)
-    recently_readonly? || Discourse.redis.exists(*keys)
+    recently_readonly? || Discourse.redis.exists?(*keys)
   end
 
   def self.pg_readonly_mode?

lib/discourse_redis.rb

@@ -193,7 +193,7 @@ class DiscourseRedis
   end
 
   # Proxy key methods through, but prefix the keys with the namespace
-  [:append, :blpop, :brpop, :brpoplpush, :decr, :decrby, :expire, :expireat, :get, :getbit, :getrange, :getset,
+  [:append, :blpop, :brpop, :brpoplpush, :decr, :decrby, :expire, :expireat, :exists, :exists?, :get, :getbit, :getrange, :getset,
    :hdel, :hexists, :hget, :hgetall, :hincrby, :hincrbyfloat, :hkeys, :hlen, :hmget, :hmset, :hset, :hsetnx, :hvals, :incr,
    :incrby, :incrbyfloat, :lindex, :linsert, :llen, :lpop, :lpush, :lpushx, :lrange, :lrem, :lset, :ltrim,
    :mapped_hmset, :mapped_hmget, :mapped_mget, :mapped_mset, :mapped_msetnx, :move, :mset,
@@ -207,19 +207,6 @@ class DiscourseRedis
     end
   end
 
-  # Implement our own because https://github.com/redis/redis-rb/issues/698 has stalled
-  def exists(*keys)
-    keys.map! { |a| "#{namespace}:#{a}" }  if @namespace
-
-    DiscourseRedis.ignore_readonly do
-      @redis.synchronize do |client|
-        client.call([:exists, *keys]) do |value|
-          value > 0
-        end
-      end
-    end
-  end
-
   def mget(*args)
     args.map! { |a| "#{namespace}:#{a}" }  if @namespace
     DiscourseRedis.ignore_readonly { @redis.mget(*args) }