DEV: Introduce TemporaryRedis and unset DISCOURSE_* env vars in the themes:isolated_test rake task (#13401)

The `themes:isolated_test` rake task will now unset all `DISCOURSE_*` env variables if `UNSET_DISCOURSE_ENV_VARS` env var is set and will also spin up a temporary redis server so the unicorn web server that's spun up for the tests doesn't leak into the "main" redis server.

lib/temporary_redis.rb

@@ -0,0 +1,107 @@
+# frozen_string_literal: true
+
+class TemporaryRedis
+  REDIS_TEMP_DIR = "/tmp/discourse_temp_redis"
+  REDIS_LOG_PATH = "#{REDIS_TEMP_DIR}/redis.log"
+  REDIS_PID_PATH = "#{REDIS_TEMP_DIR}/redis.pid"
+
+  attr_reader :instance
+
+  def initialize
+    set_redis_server_bin
+  end
+
+  def port
+    @port ||= find_free_port(11000..11900)
+  end
+
+  def start
+    return if @started
+    FileUtils.rm_rf(REDIS_TEMP_DIR)
+    Dir.mkdir(REDIS_TEMP_DIR)
+    FileUtils.touch(REDIS_LOG_PATH)
+
+    puts "Starting redis on port: #{port}"
+    @thread = Thread.new do
+      system(
+        @redis_server_bin,
+        "--port", port.to_s,
+        "--pidfile", REDIS_PID_PATH,
+        "--logfile", REDIS_LOG_PATH,
+        "--databases", "1",
+        "--save", '""',
+        "--appendonly", "no",
+        "--daemonize", "no",
+        "--maxclients", "100",
+        "--dir", REDIS_TEMP_DIR
+      )
+    end
+
+    puts "Waiting for redis server to start..."
+    success = false
+    instance = nil
+    config = {
+      port: port,
+      host: "127.0.0.1",
+      db: 0
+    }
+    start = Time.now
+    while !success
+      begin
+        instance = DiscourseRedis.new(config, namespace: true)
+        success = instance.ping == "PONG"
+      rescue Redis::CannotConnectError
+      ensure
+        if !success && (Time.now - start) >= 5
+          STDERR.puts "ERROR: Could not connect to redis in 5 seconds."
+          self.remove
+          exit(1)
+        elsif !success
+          sleep 0.1
+        end
+      end
+    end
+    puts "Redis is ready"
+    @instance = instance
+    @started = true
+  end
+
+  def remove
+    if @instance
+      @instance.shutdown
+      @thread.join
+      puts "Redis has been shutdown."
+    end
+    FileUtils.rm_rf(REDIS_TEMP_DIR)
+    @started = false
+    puts "Redis files have been cleaned up."
+  end
+
+  private
+
+  def set_redis_server_bin
+    path = `which redis-server 2> /dev/null`.strip
+    if path.size < 1
+      STDERR.puts 'ERROR: redis-server is not installed on this machine. Please install it'
+      exit(1)
+    end
+    @redis_server_bin = path
+  rescue => ex
+    STDERR.puts 'ERROR: Failed to find redis-server binary:'
+    STDERR.puts ex.inspect
+    exit(1)
+  end
+
+  def find_free_port(range)
+    range.each do |port|
+      return port if port_available?(port)
+    end
+  end
+
+  def port_available?(port)
+    TCPServer.open(port).close
+    true
+  rescue Errno::EADDRINUSE
+    false
+  end
+end