♻️ Compile Config.default using AttrVersionDefaults

Similar to the versioned defaults, this could be a source of conflicts
when merging, rebasing, or/cherry-picking feature and backport branches.
Now that all of the attributes specify their defaults, the current
version's default config can be compiled from that.

The sanity-check at the end of `config.rb` has been removed.  It was
there to protect against bad merges.  Now that `Config.default` is also
compiled from the version defaults added to each attr_accessor, the
tests in `test/net/imap/test_config.rb` are good enough.

Author: nevans

lib/net/imap/config.rb

@@ -194,7 +194,7 @@ def self.[](config)
       #
       # *NOTE:* Versioned default configs inherit #debug from Config.global, and
       # #load_defaults will not override #debug.
-      attr_accessor :debug, type: :boolean
+      attr_accessor :debug, type: :boolean, default: false
 
       # method: debug?
       # :call-seq: debug? -> boolean
@@ -491,28 +491,10 @@ def defaults_hash
         to_h.reject {|k,v| DEFAULT_TO_INHERIT.include?(k) }
       end
 
-      @default = new(
-        debug: false,
-        open_timeout: 30,
-        idle_response_timeout: 5,
-        sasl_ir: true,
-        enforce_logindisabled: true,
-        max_response_size: 512 << 20, # 512 MiB
-        responses_without_block: :warn,
-        parser_use_deprecated_uidplus_data: :up_to_max_size,
-        parser_max_deprecated_uidplus_data_size: 100,
-      ).freeze
-
-      @global = default.new
-
+      @default = AttrVersionDefaults.compile_default!
+      @global  = default.new
       AttrVersionDefaults.compile_version_defaults!
 
-      if ($VERBOSE || $DEBUG) && self[:current].to_h != self[:default].to_h
-        warn "Misconfigured Net::IMAP::Config[:current] => %p,\n" \
-             " not equal to Net::IMAP::Config[:default] => %p" % [
-                self[:current].to_h, self[:default].to_h
-              ]
-      end
     end
   end
 end

lib/net/imap/config/attr_version_defaults.rb

@@ -40,7 +40,8 @@ module AttrVersionDefaults
 
         def attr_accessor(name, defaults: nil, default: (unset = true), **kw)
           unless unset
-            defaults ||= { 0.0r => default }
+            version  = DEFAULT_TO_INHERIT.include?(name) ? nil : 0.0r
+            defaults = { version => default }
           end
           defaults&.each_pair do |version, default|
             AttrVersionDefaults.version_defaults[version] ||= {}
@@ -49,6 +50,15 @@ def attr_accessor(name, defaults: nil, default: (unset = true), **kw)
           super(name, **kw)
         end
 
+        def self.compile_default!
+          raise "Config.default already compiled" if Config.default
+          default = VERSIONS.select { _1 <= CURRENT_VERSION }
+            .filter_map { version_defaults[_1] }
+            .prepend(version_defaults.delete(nil))
+            .inject(&:merge)
+          Config.new(default).freeze
+        end
+
         def self.compile_version_defaults!
           # Temporarily assign Config.default, enabling #load_defaults(:default)
           version_defaults[:default] = Config.default