♻️ Make Config.global ractor safe

Config.global now delegates to a frozen config, and updates are handled
by swapping that frozen config for a new one.

Author: nevans

lib/net/imap/config.rb

@@ -4,6 +4,7 @@
 require_relative "config/attr_inheritance"
 require_relative "config/attr_type_coercion"
 require_relative "config/attr_version_defaults"
+require_relative "config/global"
 
 module Net
   class IMAP
@@ -632,7 +633,7 @@ def defaults_hash
       end
 
       @default = AttrVersionDefaults.compile_default!
-      @global  = default.new
+      @global  = Global.setup!
       AttrVersionDefaults.compile_version_defaults!
 
     end

lib/net/imap/config/attr_accessors.rb

@@ -33,7 +33,6 @@ def self.attr_accessor(name) # :nodoc: internal API
         def self.attributes
           instance_methods.grep(/=\z/).map { _1.to_s.delete_suffix("=").to_sym }
         end
-        private_class_method :attributes
 
         def self.struct # :nodoc: internal API
           unless defined?(self::Struct)

lib/net/imap/config/attr_type_coercion.rb

@@ -45,7 +45,7 @@ def self.safe(&b)
         else
           def self.safe(&b) nil.instance_eval(&b).freeze end
         end
-        private_class_method :safe
+        # private_class_method :safe
 
         Types = Hash.new do |h, type| type => Proc | nil; safe{type} end
         Types[:boolean] = Boolean = safe{-> {!!_1}}

lib/net/imap/config/attr_version_defaults.rb

@@ -26,14 +26,15 @@ module AttrVersionDefaults
         # See Config.version_defaults.
         singleton_class.attr_reader :version_defaults
 
-        @version_defaults = Hash.new {|h, k|
+        @version_defaults = {}
+        version_defaults.default_proc = AttrTypeCoercion.safe {->(h, k){
           # NOTE: String responds to both so the order is significant.
           # And ignore non-numeric conversion to zero, because: "wat!?".to_r == 0
           (h.fetch(k.to_r, nil) || h.fetch(k.to_f, nil) if k.is_a?(Numeric)) ||
-            (h.fetch(k.to_sym, nil) if k.respond_to?(:to_sym)) ||
-            (h.fetch(k.to_r,   nil) if k.respond_to?(:to_r) && k.to_r != 0r) ||
-            (h.fetch(k.to_f,   nil) if k.respond_to?(:to_f) && k.to_f != 0.0)
-        }
+          (h.fetch(k.to_sym, nil) if k.respond_to?(:to_sym)) ||
+          (h.fetch(k.to_r,   nil) if k.respond_to?(:to_r) && k.to_r != 0r) ||
+          (h.fetch(k.to_f,   nil) if k.respond_to?(:to_f) && k.to_f != 0.0)
+        }}
 
         # :stopdoc: internal APIs only
 

lib/net/imap/config/global.rb

@@ -1,27 +1,55 @@
-include "singleton"
+require "singleton"
 
 module Net
   class IMAP
     class Config
       class Global < Config
         include Singleton
+        extend Forwardable
+        singleton_class.extend(Forwardable)
 
-        def initialize(...)
-          super
+        singleton_class.attr_reader :snapshot
+
+        def_delegators :"self.class", :reset, :snapshot
+        protected :snapshot
+
+        def self.setup!
+          @snapshot = Config.default.new.freeze
+          AttrAccessors.attributes.each do |attr|
+            singleton_class.define_method(:"#{attr}=") do |val|
+              @snapshot = snapshot.dup.update(attr => val).freeze
+            end
+            singleton_class.def_delegator :snapshot, attr
+            def_delegators :"self.class", attr, :"#{attr}="
+          end
+          instance
+        end
+
+        def initialize
+          super(Config.default)
           @data = nil
           freeze
         end
 
-        AttrAccessors.attributes.each do |attr|
-          singleton_class.define_method(attr) { snapshot.attr }
-          singleton_class.define_method(:"#{attr}=") do |val|
-            @snapshot = shapshot.with(attr => val)
+        def new(**attrs) Config.new(self, **attrs) end
+
+        def self.reset(attr = nil)
+          if attr.nil?
+            @snapshot = Config.default.new.freeze
+            self
+          elsif snapshot.inherited?(attr)
+            nil
+          else
+            old, new = send(attr), snapshot.dup
+            new.reset(attr)
+            @snapshot = new.freeze
+            old
           end
         end
 
         protected
 
-        def data = self.class.data
+        def data = snapshot.data
 
       end
     end

test/net/imap/test_config.rb

@@ -88,7 +88,7 @@ class ConfigTest < Net::IMAP::TestCase
     assert_equal true, global.debug?
     global.reset(:debug)
     assert_equal false, global.debug?
-    refute global.frozen?
+    assert global.frozen?
   end
 
   test "Net::IMAP.config" do
@@ -158,6 +158,10 @@ class ConfigTest < Net::IMAP::TestCase
   end
 
   if defined?(Ractor)
+    test ".global is deeply frozen (and Ractor shareable)" do
+      assert Ractor.shareable?(Config.global)
+    end
+
     test ".version_defaults is deeply frozen (and Ractor shareable)" do
       assert Ractor.shareable? Config.version_defaults
     end