Dalli::Client doesn't pick up the value of MEMCACHE_SERVERS when used with Rails

[radiantshaw]

Steps to reproduce

• Create a new Rails app
• Set config.cache_store to :mem_cache_store
• Install the dalli gem
• Set the value of MEMCACHE_SERVERS env variable
• Access the Memcache server via an instance of Dalli::Client
• Now do the same with the object provided by Rails.cache

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "activesupport", "~> 6.0.4.6"
  gem "dalli", "~> 2.7.6"
end

require "active_support"
require "active_support/core_ext/object/blank"
require "minitest/autorun"

class MemCacheBugTest < Minitest::Test
  def test_dalli_client_reads_memcache_servers_env_var
    ENV.stub :[], "memcached.example.com:11211" do
      dalli_client = Dalli::Client.new
      assert_includes dalli_client.instance_variable_get(:@servers), "memcached.example.com:11211"
    end
  end

  def test_rails_cache_does_not_read_memcache_servers_env_var
    ENV.stub :[], "memcached.example.com:11211" do
      dalli_client = ActiveSupport::Cache::MemCacheStore.new.instance_variable_get(:@data)
      refute_includes dalli_client.instance_variable_get(:@servers), "memcached.example.com:11211"
    end
  end
end

Expected behavior

Rails configuration shouldn't prevent Dalli::Client instances from reading the value of MEMCACHE_SERVERS env variable.

Actual behavior

Rails configuration prevents Dalli::Client instances from reading the value of MEMCACHE_SERVERS env variable.

System configuration

Rails version: 6.0.4.6

Ruby version: 2.7.5

[fatkodima]

It was fixed in rails 6.1.0 - #40420, you need to upgrade.