Wraps any standard Logger class to provide tagging capabilities. Examples:

Logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))
Logger.tagged("BCX") { Logger.info "Stuff" }                            # Logs "[BCX] Stuff"
Logger.tagged("BCX", "Jason") { Logger.info "Stuff" }                   # Logs "[BCX] [Jason] Stuff"
Logger.tagged("BCX") { Logger.tagged("Jason") { Logger.info "Stuff" } } # Logs "[BCX] [Jason] Stuff"

This is used by the default Rails.logger as configured by Railties to make it easy to stamp log lines with subdomains, request ids, and anything else to aid debugging of multi-user production applications.

Methods
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Class Public methods
new(logger)
# File activesupport/lib/active_support/tagged_logging.rb, line 16
def initialize(logger)
  @logger = logger
  @tags   = Hash.new { |h,k| h[k] = [] }
end
Instance Public methods
add(severity, message = nil, progname = nil, &block)
# File activesupport/lib/active_support/tagged_logging.rb, line 35
def add(severity, message = nil, progname = nil, &block)
  message = (block_given? ? block.call : progname) if message.nil?
  @logger.add(severity, "#{tags_text}#{message}", progname)
end
flush()
# File activesupport/lib/active_support/tagged_logging.rb, line 48
def flush
  @tags.delete(Thread.current)
  @logger.flush if @logger.respond_to?(:flush)
end
method_missing(method, *args)
# File activesupport/lib/active_support/tagged_logging.rb, line 53
def method_missing(method, *args)
  @logger.send(method, *args)
end
silence(temporary_level = Logger::ERROR, &block)
# File activesupport/lib/active_support/tagged_logging.rb, line 30
def silence(temporary_level = Logger::ERROR, &block)
  @logger.silence(temporary_level, &block)
end
tagged(*new_tags)
# File activesupport/lib/active_support/tagged_logging.rb, line 21
def tagged(*new_tags)
  tags     = current_tags
  new_tags = Array.wrap(new_tags).flatten.reject(&:blank?)
  tags.concat new_tags
  yield
ensure
  new_tags.size.times { tags.pop }
end
Instance Protected methods
current_tags()
# File activesupport/lib/active_support/tagged_logging.rb, line 66
def current_tags
  @tags[Thread.current]
end
tags_text()
# File activesupport/lib/active_support/tagged_logging.rb, line 59
def tags_text
  tags = current_tags
  if tags.any?
    tags.collect { |tag| "[#{tag}]" }.join(" ") + " "
  end
end