# <!-- rdoc-file=lib/logger.rb -->
# Class Logger provides a simple but sophisticated logging utility that you can
# use to create one or more [event
# logs](https://en.wikipedia.org/wiki/Logging_(software)#Event_logs) for your
# program. Each such log contains a chronological sequence of entries that
# provides a record of the program's activities.
#
# ## About the Examples
#
# All examples on this page assume that Logger has been required:
#
#     require 'logger'
#
# ## Synopsis
#
# Create a log with Logger.new:
#
#     # Single log file.
#     logger = Logger.new('t.log')
#     # Size-based rotated logging: 3 10-megabyte files.
#     logger = Logger.new('t.log', 3, 10485760)
#     # Period-based rotated logging: daily (also allowed: 'weekly', 'monthly').
#     logger = Logger.new('t.log', 'daily')
#     # Log to an IO stream.
#     logger = Logger.new($stdout)
#
# Add entries (level, message) with Logger#add:
#
#     logger.add(Logger::DEBUG, 'Maximal debugging info')
#     logger.add(Logger::INFO, 'Non-error information')
#     logger.add(Logger::WARN, 'Non-error warning')
#     logger.add(Logger::ERROR, 'Non-fatal error')
#     logger.add(Logger::FATAL, 'Fatal error')
#     logger.add(Logger::UNKNOWN, 'Most severe')
#
# Close the log with Logger#close:
#
#     logger.close
#
# ## Entries
#
# You can add entries with method Logger#add:
#
#     logger.add(Logger::DEBUG, 'Maximal debugging info')
#     logger.add(Logger::INFO, 'Non-error information')
#     logger.add(Logger::WARN, 'Non-error warning')
#     logger.add(Logger::ERROR, 'Non-fatal error')
#     logger.add(Logger::FATAL, 'Fatal error')
#     logger.add(Logger::UNKNOWN, 'Most severe')
#
# These shorthand methods also add entries:
#
#     logger.debug('Maximal debugging info')
#     logger.info('Non-error information')
#     logger.warn('Non-error warning')
#     logger.error('Non-fatal error')
#     logger.fatal('Fatal error')
#     logger.unknown('Most severe')
#
# When you call any of these methods, the entry may or may not be written to the
# log, depending on the entry's severity and on the log level; see [Log
# Level](rdoc-ref:Logger@Log+Level)
#
# An entry always has:
#
# *   A severity (the required argument to #add).
# *   An automatically created timestamp.
#
#
# And may also have:
#
# *   A message.
# *   A program name.
#
#
# Example:
#
#     logger = Logger.new($stdout)
#     logger.add(Logger::INFO, 'My message.', 'mung')
#     # => I, [2022-05-07T17:21:46.536234 #20536]  INFO -- mung: My message.
#
# The default format for an entry is:
#
#     "%s, [%s #%d] %5s -- %s: %s\n"
#
# where the values to be formatted are:
#
# *   Severity (one letter).
# *   Timestamp.
# *   Process id.
# *   Severity (word).
# *   Program name.
# *   Message.
#
#
# You can use a different entry format by:
#
# *   Setting a custom format proc (affects following entries); see
#     [formatter=](Logger.html#attribute-i-formatter).
# *   Calling any of the methods above with a block (affects only the one
#     entry). Doing so can have two benefits:
#
#     *   Context: the block can evaluate the entire program context and create
#         a context-dependent message.
#     *   Performance: the block is not evaluated unless the log level permits
#         the entry actually to be written:
#
#             logger.error { my_slow_message_generator }
#
#         Contrast this with the string form, where the string is always
#         evaluated, regardless of the log level:
#
#             logger.error("#{my_slow_message_generator}")
#
#
#
# ### Severity
#
# The severity of a log entry has two effects:
#
# *   Determines whether the entry is selected for inclusion in the log; see
#     [Log Level](rdoc-ref:Logger@Log+Level).
# *   Indicates to any log reader (whether a person or a program) the relative
#     importance of the entry.
#
#
# ### Timestamp
#
# The timestamp for a log entry is generated automatically when the entry is
# created.
#
# The logged timestamp is formatted by method
# [Time#strftime](rdoc-ref:Time#strftime) using this format string:
#
#     '%Y-%m-%dT%H:%M:%S.%6N'
#
# Example:
#
#     logger = Logger.new($stdout)
#     logger.add(Logger::INFO)
#     # => I, [2022-05-07T17:04:32.318331 #20536]  INFO -- : nil
#
# You can set a different format using method #datetime_format=.
#
# ### Message
#
# The message is an optional argument to an entry method:
#
#     logger = Logger.new($stdout)
#     logger.add(Logger::INFO, 'My message')
#     # => I, [2022-05-07T18:15:37.647581 #20536]  INFO -- : My message
#
# For the default entry formatter, `Logger::Formatter`, the message object may
# be:
#
# *   A string: used as-is.
# *   An Exception: `message.message` is used.
# *   Anything else: `message.inspect` is used.
#
#
# **Note**: Logger::Formatter does not escape or sanitize the message passed to
# it. Developers should be aware that malicious data (user input) may be in the
# message, and should explicitly escape untrusted data.
#
# You can use a custom formatter to escape message data; see the example at
# [formatter=](Logger.html#attribute-i-formatter).
#
# ### Program Name
#
# The program name is an optional argument to an entry method:
#
#     logger = Logger.new($stdout)
#     logger.add(Logger::INFO, 'My message', 'mung')
#     # => I, [2022-05-07T18:17:38.084716 #20536]  INFO -- mung: My message
#
# The default program name for a new logger may be set in the call to Logger.new
# via optional keyword argument `progname`:
#
#     logger = Logger.new('t.log', progname: 'mung')
#
# The default program name for an existing logger may be set by a call to method
# #progname=:
#
#     logger.progname = 'mung'
#
# The current program name may be retrieved with method
# [progname](Logger.html#attribute-i-progname):
#
#     logger.progname # => "mung"
#
# ## Log Level
#
# The log level setting determines whether an entry is actually written to the
# log, based on the entry's severity.
#
# These are the defined severities (least severe to most severe):
#
#     logger = Logger.new($stdout)
#     logger.add(Logger::DEBUG, 'Maximal debugging info')
#     # => D, [2022-05-07T17:57:41.776220 #20536] DEBUG -- : Maximal debugging info
#     logger.add(Logger::INFO, 'Non-error information')
#     # => I, [2022-05-07T17:59:14.349167 #20536]  INFO -- : Non-error information
#     logger.add(Logger::WARN, 'Non-error warning')
#     # => W, [2022-05-07T18:00:45.337538 #20536]  WARN -- : Non-error warning
#     logger.add(Logger::ERROR, 'Non-fatal error')
#     # => E, [2022-05-07T18:02:41.592912 #20536] ERROR -- : Non-fatal error
#     logger.add(Logger::FATAL, 'Fatal error')
#     # => F, [2022-05-07T18:05:24.703931 #20536] FATAL -- : Fatal error
#     logger.add(Logger::UNKNOWN, 'Most severe')
#     # => A, [2022-05-07T18:07:54.657491 #20536]   ANY -- : Most severe
#
# The default initial level setting is Logger::DEBUG, the lowest level, which
# means that all entries are to be written, regardless of severity:
#
#     logger = Logger.new($stdout)
#     logger.level # => 0
#     logger.add(0, "My message")
#     # => D, [2022-05-11T15:10:59.773668 #20536] DEBUG -- : My message
#
# You can specify a different setting in a new logger using keyword argument
# `level` with an appropriate value:
#
#     logger = Logger.new($stdout, level: Logger::ERROR)
#     logger = Logger.new($stdout, level: 'error')
#     logger = Logger.new($stdout, level: :error)
#     logger.level # => 3
#
# With this level, entries with severity Logger::ERROR and higher are written,
# while those with lower severities are not written:
#
#     logger = Logger.new($stdout, level: Logger::ERROR)
#     logger.add(3)
#     # => E, [2022-05-11T15:17:20.933362 #20536] ERROR -- : nil
#     logger.add(2) # Silent.
#
# You can set the log level for an existing logger with method #level=:
#
#     logger.level = Logger::ERROR
#
# These shorthand methods also set the level:
#
#     logger.debug! # => 0
#     logger.info!  # => 1
#     logger.warn!  # => 2
#     logger.error! # => 3
#     logger.fatal! # => 4
#
# You can retrieve the log level with method #level.
#
#     logger.level = Logger::ERROR
#     logger.level # => 3
#
# These methods return whether a given level is to be written:
#
#     logger.level = Logger::ERROR
#     logger.debug? # => false
#     logger.info?  # => false
#     logger.warn?  # => false
#     logger.error? # => true
#     logger.fatal? # => true
#
# ## Log File Rotation
#
# By default, a log file is a single file that grows indefinitely (until
# explicitly closed); there is no file rotation.
#
# To keep log files to a manageable size, you can use *log* *file* *rotation*,
# which uses multiple log files:
#
# *   Each log file has entries for a non-overlapping time interval.
# *   Only the most recent log file is open and active; the others are closed
#     and inactive.
#
#
# ### Size-Based Rotation
#
# For size-based log file rotation, call Logger.new with:
#
# *   Argument `logdev` as a file path.
# *   Argument `shift_age` with a positive integer: the number of log files to
#     be in the rotation.
# *   Argument `shift_size` as a positive integer: the maximum size (in bytes)
#     of each log file; defaults to 1048576 (1 megabyte).
#
#
# Examples:
#
#     logger = Logger.new('t.log', 3)           # Three 1-megabyte files.
#     logger = Logger.new('t.log', 5, 10485760) # Five 10-megabyte files.
#
# For these examples, suppose:
#
#     logger = Logger.new('t.log', 3)
#
# Logging begins in the new log file, `t.log`; the log file is "full" and ready
# for rotation when a new entry would cause its size to exceed `shift_size`.
#
# The first time `t.log` is full:
#
# *   `t.log` is closed and renamed to `t.log.0`.
# *   A new file `t.log` is opened.
#
#
# The second time `t.log` is full:
#
# *   +t.log.0 is renamed as `t.log.1`.
# *   `t.log` is closed and renamed to `t.log.0`.
# *   A new file `t.log` is opened.
#
#
# Each subsequent time that `t.log` is full, the log files are rotated:
#
# *   `t.log.1` is removed.
# *   +t.log.0 is renamed as `t.log.1`.
# *   `t.log` is closed and renamed to `t.log.0`.
# *   A new file `t.log` is opened.
#
#
# ### Periodic Rotation
#
# For periodic rotation, call Logger.new with:
#
# *   Argument `logdev` as a file path.
# *   Argument `shift_age` as a string period indicator.
#
#
# Examples:
#
#     logger = Logger.new('t.log', 'daily')   # Rotate log files daily.
#     logger = Logger.new('t.log', 'weekly')  # Rotate log files weekly.
#     logger = Logger.new('t.log', 'monthly') # Rotate log files monthly.
#
# Example:
#
#     logger = Logger.new('t.log', 'daily')
#
# When the given period expires:
#
# *   The base log file, `t.log` is closed and renamed with a date-based suffix
#     such as `t.log.20220509`.
# *   A new log file `t.log` is opened.
# *   Nothing is removed.
#
#
# The default format for the suffix is `'%Y%m%d'`, which produces a suffix
# similar to the one above. You can set a different format using create-time
# option `shift_period_suffix`; see details and suggestions at
# [Time#strftime](rdoc-ref:Time#strftime).
#
class Logger
  interface _WriteCloser
    def write: (_ToS) -> untyped

    def close: () -> untyped
  end
  type logdev = _WriteCloser | String

  include Logger::Severity

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - <<(msg)
  # -->
  # Writes the given `msg` to the log with no formatting; returns the number of
  # characters written, or `nil` if no log device exists:
  #
  #     logger = Logger.new($stdout)
  #     logger << 'My message.' # => 10
  #
  # Output:
  #
  #     My message.
  #
  def <<: (untyped msg) -> (untyped | nil)

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - add(severity, message = nil, progname = nil) { || ... }
  # -->
  # Creates a log entry, which may or may not be written to the log, depending on
  # the entry's severity and on the log level. See [Log
  # Level](rdoc-ref:Logger@Log+Level) and [Entries](rdoc-ref:Logger@Entries) for
  # details.
  #
  # Examples:
  #
  #     logger = Logger.new($stdout, progname: 'mung')
  #     logger.add(Logger::INFO)
  #     logger.add(Logger::ERROR, 'No good')
  #     logger.add(Logger::ERROR, 'No good', 'gnum')
  #
  # Output:
  #
  #     I, [2022-05-12T16:25:31.469726 #36328]  INFO -- mung: mung
  #     E, [2022-05-12T16:25:55.349414 #36328] ERROR -- mung: No good
  #     E, [2022-05-12T16:26:35.841134 #36328] ERROR -- gnum: No good
  #
  # These convenience methods have implicit severity:
  #
  # *   #debug.
  # *   #info.
  # *   #warn.
  # *   #error.
  # *   #fatal.
  # *   #unknown.
  #
  def add: (Integer severity, ?untyped message, ?untyped progname) ?{ () -> untyped } -> true

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - close()
  # -->
  # Closes the logger; returns `nil`:
  #
  #     logger = Logger.new('t.log')
  #     logger.close       # => nil
  #     logger.info('foo') # Prints "log writing failed. closed stream"
  #
  # Related: Logger#reopen.
  #
  def close: () -> untyped

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - datetime_format()
  # -->
  # Returns the date-time format; see #datetime_format=.
  #
  def datetime_format: () -> String?

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - datetime_format=(datetime_format)
  # -->
  # Sets the date-time format.
  #
  # Argument `datetime_format` should be either of these:
  #
  # *   A string suitable for use as a format for method
  #     [Time#strftime](rdoc-ref:Time#strftime).
  # *   `nil`: the logger uses `'%Y-%m-%dT%H:%M:%S.%6N'`.
  #
  def datetime_format=: (String datetime_format) -> String
                      | (nil datetime_format) -> nil

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - debug(progname = nil, &block)
  # -->
  # Equivalent to calling #add with severity `Logger::DEBUG`.
  #
  def debug: (?untyped progname) ?{ () -> untyped } -> true

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - debug!()
  # -->
  # Sets the log level to Logger::DEBUG. See [Log
  # Level](rdoc-ref:Logger@Log+Level).
  #
  def debug!: () -> Integer

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - debug?()
  # -->
  # Returns `true` if the log level allows entries with severity Logger::DEBUG to
  # be written, `false` otherwise. See [Log Level](rdoc-ref:Logger@Log+Level).
  #
  def debug?: () -> bool

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - error(progname = nil, &block)
  # -->
  # Equivalent to calling #add with severity `Logger::ERROR`.
  #
  def error: (?untyped progname) ?{ () -> untyped } -> true

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - error!()
  # -->
  # Sets the log level to Logger::ERROR. See [Log
  # Level](rdoc-ref:Logger@Log+Level).
  #
  def error!: () -> Integer

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - error?()
  # -->
  # Returns `true` if the log level allows entries with severity Logger::ERROR to
  # be written, `false` otherwise. See [Log Level](rdoc-ref:Logger@Log+Level).
  #
  def error?: () -> bool

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - fatal(progname = nil, &block)
  # -->
  # Equivalent to calling #add with severity `Logger::FATAL`.
  #
  def fatal: (?untyped progname) ?{ () -> untyped } -> true

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - fatal!()
  # -->
  # Sets the log level to Logger::FATAL. See [Log
  # Level](rdoc-ref:Logger@Log+Level).
  #
  def fatal!: () -> Integer

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - fatal?()
  # -->
  # Returns `true` if the log level allows entries with severity Logger::FATAL to
  # be written, `false` otherwise. See [Log Level](rdoc-ref:Logger@Log+Level).
  #
  def fatal?: () -> bool

  # <!-- rdoc-file=lib/logger.rb -->
  # Sets or retrieves the logger entry formatter proc.
  #
  # When `formatter` is `nil`, the logger uses Logger::Formatter.
  #
  # When `formatter` is a proc, a new entry is formatted by the proc, which is
  # called with four arguments:
  #
  # *   `severity`: The severity of the entry.
  # *   `time`: A Time object representing the entry's timestamp.
  # *   `progname`: The program name for the entry.
  # *   `msg`: The message for the entry (string or string-convertible object).
  #
  #
  # The proc should return a string containing the formatted entry.
  #
  # This custom formatter uses [String#dump](rdoc-ref:String#dump) to escape the
  # message string:
  #
  #     logger = Logger.new($stdout, progname: 'mung')
  #     original_formatter = logger.formatter || Logger::Formatter.new
  #     logger.formatter = proc { |severity, time, progname, msg|
  #       original_formatter.call(severity, time, progname, msg.dump)
  #     }
  #     logger.add(Logger::INFO, "hello \n ''")
  #     logger.add(Logger::INFO, "\f\x00\xff\\\"")
  #
  # Output:
  #
  #     I, [2022-05-13T13:16:29.637488 #8492]  INFO -- mung: "hello \n ''"
  #     I, [2022-05-13T13:16:29.637610 #8492]  INFO -- mung: "\f\x00\xFF\\\""
  #
  def formatter: () -> (_Formatter | nil)

  # <!-- rdoc-file=lib/logger.rb -->
  # Sets or retrieves the logger entry formatter proc.
  #
  # When `formatter` is `nil`, the logger uses Logger::Formatter.
  #
  # When `formatter` is a proc, a new entry is formatted by the proc, which is
  # called with four arguments:
  #
  # *   `severity`: The severity of the entry.
  # *   `time`: A Time object representing the entry's timestamp.
  # *   `progname`: The program name for the entry.
  # *   `msg`: The message for the entry (string or string-convertible object).
  #
  #
  # The proc should return a string containing the formatted entry.
  #
  # This custom formatter uses [String#dump](rdoc-ref:String#dump) to escape the
  # message string:
  #
  #     logger = Logger.new($stdout, progname: 'mung')
  #     original_formatter = logger.formatter || Logger::Formatter.new
  #     logger.formatter = proc { |severity, time, progname, msg|
  #       original_formatter.call(severity, time, progname, msg.dump)
  #     }
  #     logger.add(Logger::INFO, "hello \n ''")
  #     logger.add(Logger::INFO, "\f\x00\xff\\\"")
  #
  # Output:
  #
  #     I, [2022-05-13T13:16:29.637488 #8492]  INFO -- mung: "hello \n ''"
  #     I, [2022-05-13T13:16:29.637610 #8492]  INFO -- mung: "\f\x00\xFF\\\""
  #
  def formatter=: (_Formatter) -> _Formatter
                | (nil) -> nil

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - info(progname = nil, &block)
  # -->
  # Equivalent to calling #add with severity `Logger::INFO`.
  #
  def info: (?untyped progname) ?{ () -> untyped } -> true

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - info!()
  # -->
  # Sets the log level to Logger::INFO. See [Log
  # Level](rdoc-ref:Logger@Log+Level).
  #
  def info!: () -> Integer

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - info?()
  # -->
  # Returns `true` if the log level allows entries with severity Logger::INFO to
  # be written, `false` otherwise. See [Log Level](rdoc-ref:Logger@Log+Level).
  #
  def info?: () -> bool

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - level()
  # -->
  # Logging severity threshold (e.g. `Logger::INFO`).
  #
  def level: () -> Integer

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - level=(severity)
  # -->
  # Sets the log level; returns `severity`. See [Log
  # Level](rdoc-ref:Logger@Log+Level).
  #
  # Argument `severity` may be an integer, a string, or a symbol:
  #
  #     logger.level = Logger::ERROR # => 3
  #     logger.level = 3             # => 3
  #     logger.level = 'error'       # => "error"
  #     logger.level = :error        # => :error
  #
  # Logger#sev_threshold= is an alias for Logger#level=.
  #
  def level=: (Integer | interned severity) -> Integer

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - log(severity, message = nil, progname = nil)
  # -->
  #
  alias log add

  # <!-- rdoc-file=lib/logger.rb -->
  # Program name to include in log messages.
  #
  def progname: () -> untyped

  # <!-- rdoc-file=lib/logger.rb -->
  # Program name to include in log messages.
  #
  def progname=: (untyped) -> untyped

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - reopen(logdev = nil)
  # -->
  # Sets the logger's output stream:
  #
  # *   If `logdev` is `nil`, reopens the current output stream.
  # *   If `logdev` is a filepath, opens the indicated file for append.
  # *   If `logdev` is an IO stream (usually `$stdout`, `$stderr`, or an open File
  #     object), opens the stream for append.
  #
  #
  # Example:
  #
  #     logger = Logger.new('t.log')
  #     logger.add(Logger::ERROR, 'one')
  #     logger.close
  #     logger.add(Logger::ERROR, 'two') # Prints 'log writing failed. closed stream'
  #     logger.reopen
  #     logger.add(Logger::ERROR, 'three')
  #     logger.close
  #     File.readlines('t.log')
  #     # =>
  #     # ["# Logfile created on 2022-05-12 14:21:19 -0500 by logger.rb/v1.5.0\n",
  #     #  "E, [2022-05-12T14:21:27.596726 #22428] ERROR -- : one\n",
  #     #  "E, [2022-05-12T14:23:05.847241 #22428] ERROR -- : three\n"]
  #
  def reopen: () -> self
            | (logdev?) -> self

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - sev_threshold()
  # -->
  #
  alias sev_threshold level

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - sev_threshold=(severity)
  # -->
  #
  alias sev_threshold= level=

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - unknown(progname = nil, &block)
  # -->
  # Equivalent to calling #add with severity `Logger::UNKNOWN`.
  #
  def unknown: (?untyped progname) ?{ () -> untyped } -> true

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - warn(progname = nil, &block)
  # -->
  # Equivalent to calling #add with severity `Logger::WARN`.
  #
  def warn: (?untyped progname) ?{ () -> untyped } -> true

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - warn!()
  # -->
  # Sets the log level to Logger::WARN. See [Log
  # Level](rdoc-ref:Logger@Log+Level).
  #
  def warn!: () -> Integer

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - warn?()
  # -->
  # Returns `true` if the log level allows entries with severity Logger::WARN to
  # be written, `false` otherwise. See [Log Level](rdoc-ref:Logger@Log+Level).
  #
  def warn?: () -> bool

  private

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - format_message(severity, datetime, progname, msg)
  # -->
  #
  def format_message: (String severity, Time datetime, untyped progname, untyped msg) -> _ToS

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - format_severity(severity)
  # -->
  #
  def format_severity: (Integer severity) -> String

  # <!--
  #   rdoc-file=lib/logger.rb
  #   - Logger.new(logdev, shift_age = 0, shift_size = 1048576, **options)
  # -->
  # With the single argument `logdev`, returns a new logger with all default
  # options:
  #
  #     Logger.new('t.log') # => #<Logger:0x000001e685dc6ac8>
  #
  # Argument `logdev` must be one of:
  #
  # *   A string filepath: entries are to be written to the file at that path; if
  #     the file at that path exists, new entries are appended.
  # *   An IO stream (typically +$stdout+, +$stderr+. or an open file): entries
  #     are to be written to the given stream.
  # *   `nil` or `File::NULL`: no entries are to be written.
  #
  #
  # Examples:
  #
  #     Logger.new('t.log')
  #     Logger.new($stdout)
  #
  # The keyword options are:
  #
  # *   `level`: sets the log level; default value is Logger::DEBUG. See [Log
  #     Level](rdoc-ref:Logger@Log+Level):
  #
  #         Logger.new('t.log', level: Logger::ERROR)
  #
  # *   `progname`: sets the default program name; default is `nil`. See [Program
  #     Name](rdoc-ref:Logger@Program+Name):
  #
  #         Logger.new('t.log', progname: 'mung')
  #
  # *   `formatter`: sets the entry formatter; default is `nil`. See
  #     [formatter=](Logger.html#attribute-i-formatter).
  # *   `datetime_format`: sets the format for entry timestamp; default is `nil`.
  #     See #datetime_format=.
  # *   `binmode`: sets whether the logger writes in binary mode; default is
  #     `false`.
  # *   `shift_period_suffix`: sets the format for the filename suffix for
  #     periodic log file rotation; default is `'%Y%m%d'`. See [Periodic
  #     Rotation](rdoc-ref:Logger@Periodic+Rotation).
  #
  def initialize: (logdev? logdev, ?Numeric | String shift_age, ?Integer shift_size, ?shift_period_suffix: String, ?binmode: boolish, ?datetime_format: String, ?formatter: _Formatter, ?progname: String, ?level: Integer | interned) -> void
end

Logger::ProgName: String

# <!-- rdoc-file=lib/logger.rb -->
# Severity label for logging (max 5 chars).
#
Logger::SEV_LABEL: Array[String]

Logger::VERSION: String