🔧 Add very basic Config class (currently unused)

Nothing uses this new Config class yet.  Currently, it holds only three
config options: `debug`, `open_timeout`, and `idle_response_timeout`,
but more will be added soon.

This version does not have any support for inheritance.  That will be
added in one of the next commits.

Author: nevans

lib/net/imap.rb

@@ -725,6 +725,8 @@ class IMAP < Protocol
       "UTF8=ONLY" => "UTF8=ACCEPT",
     }.freeze
 
+    autoload :Config,      File.expand_path("imap/config",       __dir__)
+
     autoload :SASL,        File.expand_path("imap/sasl",         __dir__)
     autoload :SASLAdapter, File.expand_path("imap/sasl_adapter", __dir__)
     autoload :StringPrep,  File.expand_path("imap/stringprep",   __dir__)

lib/net/imap/config.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+# :markup: markdown
+
+module Net
+  class IMAP
+
+    # Net::IMAP::Config stores configuration options for Net::IMAP clients.
+    #
+    # ## Thread Safety
+    #
+    # *NOTE:* Updates to config objects are not synchronized for thread-safety.
+    #
+    class Config
+
+      # The debug mode (boolean)
+      attr_accessor :debug
+      alias debug? debug
+
+      # Seconds to wait until a connection is opened.
+      #
+      # If the IMAP object cannot open a connection within this time,
+      # it raises a Net::OpenTimeout exception.  See Net::IMAP.new.
+      attr_accessor :open_timeout
+
+      # Seconds to wait until an IDLE response is received, after
+      # the client asks to leave the IDLE state.  See Net::IMAP#idle_done.
+      attr_accessor :idle_response_timeout
+
+      # Creates a new config object and initialize its attribute with +attrs+.
+      #
+      # If a block is given, the new config object is yielded to it.
+      def initialize(**attrs)
+        super()
+        attrs.each do send(:"#{_1}=", _2) end
+        yield self if block_given?
+      end
+
+    end
+  end
+end

test/net/imap/test_config.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require "net/imap"
+require "test/unit"
+
+class ConfigTest < Test::Unit::TestCase
+  Config = Net::IMAP::Config
+
+  test "#debug" do
+    assert Config.new(debug: true).debug
+    refute Config.new(debug: false).debug
+    assert Config.new(debug: true).debug?
+    refute Config.new(debug: false).debug?
+    config = Config.new do |c|
+      c.debug = true
+    end
+    assert config.debug
+    config = Config.new
+    config.debug = true
+    assert config.debug
+    assert config.debug?
+    config.debug = false
+    refute config.debug
+    refute config.debug?
+  end
+
+end