Merge branch 'master' into unlock-minitest

24 files changed, 438 insertions, 111 deletions

diff --git a/activesupport/lib/active_support.rb b/activesupport/lib/active_support.rb
index 03e3ce821a..a667fbb54a 100644
--- a/activesupport/lib/active_support.rb
+++ b/activesupport/lib/active_support.rb
@@ -32,6 +32,7 @@ module ActiveSupport
   extend ActiveSupport::Autoload
 
   autoload :Concern
+  autoload :CurrentAttributes
   autoload :Dependencies
   autoload :DescendantsTracker
   autoload :ExecutionWrapper
diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb
index 4d8c2046e8..a1093a2e23 100644
--- a/activesupport/lib/active_support/cache.rb
+++ b/activesupport/lib/active_support/cache.rb
@@ -88,10 +88,11 @@ module ActiveSupport
       private
         def retrieve_cache_key(key)
           case
-          when key.respond_to?(:cache_key) then key.cache_key
-          when key.is_a?(Array)            then key.map { |element| retrieve_cache_key(element) }.to_param
-          when key.respond_to?(:to_a)      then retrieve_cache_key(key.to_a)
-          else                                  key.to_param
+          when key.respond_to?(:cache_key_with_version) then key.cache_key_with_version
+          when key.respond_to?(:cache_key)              then key.cache_key
+          when key.is_a?(Array)                         then key.map { |element| retrieve_cache_key(element) }.to_param
+          when key.respond_to?(:to_a)                   then retrieve_cache_key(key.to_a)
+          else                                               key.to_param
           end.to_s
         end
 
@@ -219,6 +220,10 @@ module ActiveSupport
       #   cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 5.minutes)
       #   cache.write(key, value, expires_in: 1.minute) # Set a lower value for one entry
       #
+      # Setting <tt>:version</tt> verifies the cache stored under <tt>name</tt>
+      # is of the same version. nil is returned on mismatches despite contents.
+      # This feature is used to support recyclable cache keys.
+      #
       # Setting <tt>:race_condition_ttl</tt> is very useful in situations where
       # a cache entry is used very frequently and is under heavy load. If a
       # cache expires and due to heavy load several different processes will try
@@ -287,6 +292,7 @@ module ActiveSupport
           instrument(:read, name, options) do |payload|
             cached_entry = read_entry(key, options) unless options[:force]
             entry = handle_expired_entry(cached_entry, key, options)
+            entry = nil if entry && entry.mismatched?(normalize_version(name, options))
             payload[:super_operation] = :fetch if payload
             payload[:hit] = !!entry if payload
           end
@@ -303,21 +309,30 @@ module ActiveSupport
         end
       end
 
-      # Fetches data from the cache, using the given key. If there is data in
+      # Reads data from the cache, using the given key. If there is data in
       # the cache with the given key, then that data is returned. Otherwise,
       # +nil+ is returned.
       #
+      # Note, if data was written with the <tt>:expires_in<tt> or <tt>:version</tt> options,
+      # both of these conditions are applied before the data is returned.
+      #
       # Options are passed to the underlying cache implementation.
       def read(name, options = nil)
         options = merged_options(options)
-        key = normalize_key(name, options)
+        key     = normalize_key(name, options)
+        version = normalize_version(name, options)
+
         instrument(:read, name, options) do |payload|
           entry = read_entry(key, options)
+
           if entry
             if entry.expired?
               delete_entry(key, options)
               payload[:hit] = false if payload
               nil
+            elsif entry.mismatched?(version)
+              payload[:hit] = false if payload
+              nil
             else
               payload[:hit] = true if payload
               entry.value
@@ -341,11 +356,15 @@ module ActiveSupport
 
         results = {}
         names.each do |name|
-          key = normalize_key(name, options)
-          entry = read_entry(key, options)
+          key     = normalize_key(name, options)
+          version = normalize_version(name, options)
+          entry   = read_entry(key, options)
+
           if entry
             if entry.expired?
               delete_entry(key, options)
+            elsif entry.mismatched?(version)
+              # Skip mismatched versions
             else
               results[name] = entry.value
             end
@@ -396,7 +415,7 @@ module ActiveSupport
         options = merged_options(options)
 
         instrument(:write, name, options) do
-          entry = Entry.new(value, options)
+          entry = Entry.new(value, options.merge(version: normalize_version(name, options)))
           write_entry(normalize_key(name, options), entry, options)
         end
       end
@@ -420,7 +439,7 @@ module ActiveSupport
 
         instrument(:exist?, name) do
           entry = read_entry(normalize_key(name, options), options)
-          (entry && !entry.expired?) || false
+          (entry && !entry.expired? && !entry.mismatched?(normalize_version(name, options))) || false
         end
       end
 
@@ -517,6 +536,16 @@ module ActiveSupport
           end
         end
 
+        # Prefixes a key with the namespace. Namespace and key will be delimited
+        # with a colon.
+        def normalize_key(key, options)
+          key = expanded_key(key)
+          namespace = options[:namespace] if options
+          prefix = namespace.is_a?(Proc) ? namespace.call : namespace
+          key = "#{prefix}:#{key}" if prefix
+          key
+        end
+
         # Expands key to be a consistent string value. Invokes +cache_key+ if
         # object responds to +cache_key+. Otherwise, +to_param+ method will be
         # called. If the key is a Hash, then keys will be sorted alphabetically.
@@ -537,14 +566,16 @@ module ActiveSupport
           key.to_param
         end
 
-        # Prefixes a key with the namespace. Namespace and key will be delimited
-        # with a colon.
-        def normalize_key(key, options)
-          key = expanded_key(key)
-          namespace = options[:namespace] if options
-          prefix = namespace.is_a?(Proc) ? namespace.call : namespace
-          key = "#{prefix}:#{key}" if prefix
-          key
+        def normalize_version(key, options = nil)
+          (options && options[:version].try(:to_param)) || expanded_version(key)
+        end
+
+        def expanded_version(key)
+          case
+          when key.respond_to?(:cache_version) then key.cache_version.to_param
+          when key.is_a?(Array)                then key.map { |element| expanded_version(element) }.compact.to_param
+          when key.respond_to?(:to_a)          then expanded_version(key.to_a)
+          end
         end
 
         def instrument(operation, key, options = nil)
@@ -591,13 +622,16 @@ module ActiveSupport
         end
     end
 
-    # This class is used to represent cache entries. Cache entries have a value and an optional
-    # expiration time. The expiration time is used to support the :race_condition_ttl option
-    # on the cache.
+    # This class is used to represent cache entries. Cache entries have a value, an optional
+    # expiration time, and an optional version. The expiration time is used to support the :race_condition_ttl option
+    # on the cache. The version is used to support the :version option on the cache for rejecting
+    # mismatches.
     #
     # Since cache entries in most instances will be serialized, the internals of this class are highly optimized
     # using short instance variable names that are lazily defined.
     class Entry # :nodoc:
+      attr_reader :version
+
       DEFAULT_COMPRESS_LIMIT = 16.kilobytes
 
       # Creates a new cache entry for the specified value. Options supported are
@@ -610,6 +644,7 @@ module ActiveSupport
           @value = value
         end
 
+        @version    = options[:version]
         @created_at = Time.now.to_f
         @expires_in = options[:expires_in]
         @expires_in = @expires_in.to_f if @expires_in
@@ -619,6 +654,10 @@ module ActiveSupport
         compressed? ? uncompress(@value) : @value
       end
 
+      def mismatched?(version)
+        @version && version && @version != version
+      end
+
       # Checks if the entry is expired. The +expires_in+ parameter can override
       # the value set when the entry was created.
       def expired?
diff --git a/activesupport/lib/active_support/cache/mem_cache_store.rb b/activesupport/lib/active_support/cache/mem_cache_store.rb
index e09cee3335..06fa9f67ad 100644
--- a/activesupport/lib/active_support/cache/mem_cache_store.rb
+++ b/activesupport/lib/active_support/cache/mem_cache_store.rb
@@ -97,12 +97,18 @@ module ActiveSupport
         options = merged_options(options)
 
         keys_to_names = Hash[names.map { |name| [normalize_key(name, options), name] }]
+
         raw_values = @data.get_multi(keys_to_names.keys)
         values = {}
+
         raw_values.each do |key, value|
           entry = deserialize_entry(value)
-          values[keys_to_names[key]] = entry.value unless entry.expired?
+
+          unless entry.expired? || entry.mismatched?(normalize_version(keys_to_names[key], options))
+            values[keys_to_names[key]] = entry.value
+          end
         end
+
         values
       end
 
diff --git a/activesupport/lib/active_support/cache/strategy/local_cache.rb b/activesupport/lib/active_support/cache/strategy/local_cache.rb
index 672eb2bb80..91875a56f5 100644
--- a/activesupport/lib/active_support/cache/strategy/local_cache.rb
+++ b/activesupport/lib/active_support/cache/strategy/local_cache.rb
@@ -115,7 +115,12 @@ module ActiveSupport
           end
 
           def write_entry(key, entry, options)
-            local_cache.write_entry(key, entry, options) if local_cache
+            if options[:unless_exist]
+              local_cache.delete_entry(key, options) if local_cache
+            else
+              local_cache.write_entry(key, entry, options) if local_cache
+            end
+
             super
           end
 
diff --git a/activesupport/lib/active_support/callbacks.rb b/activesupport/lib/active_support/callbacks.rb
index d771cab68b..ddfa91a342 100644
--- a/activesupport/lib/active_support/callbacks.rb
+++ b/activesupport/lib/active_support/callbacks.rb
@@ -62,8 +62,7 @@ module ActiveSupport
 
     included do
       extend ActiveSupport::DescendantsTracker
-      class_attribute :__callbacks, instance_writer: false
-      self.__callbacks ||= {}
+      class_attribute :__callbacks, instance_writer: false, default: {}
     end
 
     CALLBACK_FILTER_TYPES = [:before, :after, :around]
diff --git a/activesupport/lib/active_support/core_ext.rb b/activesupport/lib/active_support/core_ext.rb
index f397f658f3..42e0acf66a 100644
--- a/activesupport/lib/active_support/core_ext.rb
+++ b/activesupport/lib/active_support/core_ext.rb
@@ -1,3 +1,3 @@
-(Dir["#{File.dirname(__FILE__)}/core_ext/*.rb"]).each do |path|
+Dir.glob(File.expand_path("core_ext/*.rb", __dir__)).each do |path|
   require path
 end
diff --git a/activesupport/lib/active_support/core_ext/class/attribute.rb b/activesupport/lib/active_support/core_ext/class/attribute.rb
index ba422f9071..8caddcd5c3 100644
--- a/activesupport/lib/active_support/core_ext/class/attribute.rb
+++ b/activesupport/lib/active_support/core_ext/class/attribute.rb
@@ -68,11 +68,16 @@ class Class
   #   object.setting = false  # => NoMethodError
   #
   # To opt out of both instance methods, pass <tt>instance_accessor: false</tt>.
+  #
+  # To set a default value for the attribute, pass <tt>default:</tt>, like so:
+  #
+  #   class_attribute :settings, default: {}
   def class_attribute(*attrs)
     options = attrs.extract_options!
-    instance_reader = options.fetch(:instance_accessor, true) && options.fetch(:instance_reader, true)
-    instance_writer = options.fetch(:instance_accessor, true) && options.fetch(:instance_writer, true)
+    instance_reader    = options.fetch(:instance_accessor, true) && options.fetch(:instance_reader, true)
+    instance_writer    = options.fetch(:instance_accessor, true) && options.fetch(:instance_writer, true)
     instance_predicate = options.fetch(:instance_predicate, true)
+    default_value      = options.fetch(:default, nil)
 
     attrs.each do |name|
       remove_possible_singleton_method(name)
@@ -123,6 +128,10 @@ class Class
         remove_possible_method "#{name}="
         attr_writer name
       end
+
+      unless default_value.nil?
+        self.send("#{name}=", default_value)
+      end
     end
   end
 end
diff --git a/activesupport/lib/active_support/core_ext/date_time/compatibility.rb b/activesupport/lib/active_support/core_ext/date_time/compatibility.rb
index eb8b8b2c65..870391aeaa 100644
--- a/activesupport/lib/active_support/core_ext/date_time/compatibility.rb
+++ b/activesupport/lib/active_support/core_ext/date_time/compatibility.rb
@@ -1,4 +1,5 @@
 require "active_support/core_ext/date_and_time/compatibility"
+require "active_support/core_ext/module/remove_method"
 
 class DateTime
   include DateAndTime::Compatibility
diff --git a/activesupport/lib/active_support/core_ext/module/delegation.rb b/activesupport/lib/active_support/core_ext/module/delegation.rb
index 85ab739095..13f3894e6c 100644
--- a/activesupport/lib/active_support/core_ext/module/delegation.rb
+++ b/activesupport/lib/active_support/core_ext/module/delegation.rb
@@ -219,48 +219,43 @@ class Module
   # When building decorators, a common pattern may emerge:
   #
   #   class Partition
-  #     def initialize(first_event)
-  #       @events = [ first_event ]
+  #     def initialize(event)
+  #       @event = event
   #     end
   #
-  #     def people
-  #       if @events.first.detail.people.any?
-  #         @events.collect { |e| Array(e.detail.people) }.flatten.uniq
-  #       else
-  #         @events.collect(&:creator).uniq
-  #       end
+  #     def person
+  #       @event.detail.person || @event.creator
   #     end
   #
   #     private
   #       def respond_to_missing?(name, include_private = false)
-  #         @events.respond_to?(name, include_private)
+  #         @event.respond_to?(name, include_private)
   #       end
   #
   #       def method_missing(method, *args, &block)
-  #         @events.send(method, *args, &block)
+  #         @event.send(method, *args, &block)
   #       end
   #   end
   #
-  # With `Module#delegate_missing_to`, the above is condensed to:
+  # With <tt>Module#delegate_missing_to</tt>, the above is condensed to:
   #
   #   class Partition
-  #     delegate_missing_to :@events
+  #     delegate_missing_to :@event
   #
-  #     def initialize(first_event)
-  #       @events = [ first_event ]
+  #     def initialize(event)
+  #       @event = event
   #     end
   #
-  #     def people
-  #       if @events.first.detail.people.any?
-  #         @events.collect { |e| Array(e.detail.people) }.flatten.uniq
-  #       else
-  #         @events.collect(&:creator).uniq
-  #       end
+  #     def person
+  #       @event.detail.person || @event.creator
   #     end
   #   end
   #
-  # The target can be anything callable within the object. E.g. instance
-  # variables, methods, constants and the likes.
+  # The target can be anything callable within the object, e.g. instance
+  # variables, methods, constants, etc.
+  #
+  # The delegated method must be public on the target, otherwise it will
+  # raise +NoMethodError+.
   def delegate_missing_to(target)
     target = target.to_s
     target = "self.#{target}" if DELEGATION_RESERVED_METHOD_NAMES.include?(target)
diff --git a/activesupport/lib/active_support/current_attributes.rb b/activesupport/lib/active_support/current_attributes.rb
new file mode 100644
index 0000000000..872b0663c7
--- /dev/null
+++ b/activesupport/lib/active_support/current_attributes.rb
@@ -0,0 +1,193 @@
+module ActiveSupport
+  # Abstract super class that provides a thread-isolated attributes singleton, which resets automatically
+  # before and after each request. This allows you to keep all the per-request attributes easily
+  # available to the whole system.
+  #
+  # The following full app-like example demonstrates how to use a Current class to
+  # facilitate easy access to the global, per-request attributes without passing them deeply
+  # around everywhere:
+  #
+  #   # app/models/current.rb
+  #   class Current < ActiveSupport::CurrentAttributes
+  #     attribute :account, :user
+  #     attribute :request_id, :user_agent, :ip_address
+  #
+  #     resets { Time.zone = nil }
+  #
+  #     def user=(user)
+  #       super
+  #       self.account = user.account
+  #       Time.zone    = user.time_zone
+  #     end
+  #   end
+  #
+  #   # app/controllers/concerns/authentication.rb
+  #   module Authentication
+  #     extend ActiveSupport::Concern
+  #
+  #     included do
+  #       before_action :authenticate
+  #     end
+  #
+  #     private
+  #       def authenticate
+  #         if authenticated_user = User.find_by(id: cookies.signed[:user_id])
+  #           Current.user = authenticated_user
+  #         else
+  #           redirect_to new_session_url
+  #         end
+  #       end
+  #   end
+  #
+  #   # app/controllers/concerns/set_current_request_details.rb
+  #   module SetCurrentRequestDetails
+  #     extend ActiveSupport::Concern
+  #
+  #     included do
+  #       before_action do
+  #         Current.request_id = request.uuid
+  #         Current.user_agent = request.user_agent
+  #         Current.ip_address = request.ip
+  #       end
+  #     end
+  #   end
+  #
+  #   class ApplicationController < ActionController::Base
+  #     include Authentication
+  #     include SetCurrentRequestDetails
+  #   end
+  #
+  #   class MessagesController < ApplicationController
+  #     def create
+  #       Current.account.messages.create(message_params)
+  #     end
+  #   end
+  #
+  #   class Message < ApplicationRecord
+  #     belongs_to :creator, default: -> { Current.user }
+  #     after_create { |message| Event.create(record: message) }
+  #   end
+  #
+  #   class Event < ApplicationRecord
+  #     before_create do
+  #       self.request_id = Current.request_id
+  #       self.user_agent = Current.user_agent
+  #       self.ip_address = Current.ip_address
+  #     end
+  #   end
+  #
+  # A word of caution: It's easy to overdo a global singleton like Current and tangle your model as a result.
+  # Current should only be used for a few, top-level globals, like account, user, and request details.
+  # The attributes stuck in Current should be used by more or less all actions on all requests. If you start
+  # sticking controller-specific attributes in there, you're going to create a mess.
+  class CurrentAttributes
+    include ActiveSupport::Callbacks
+    define_callbacks :reset
+
+    class << self
+      # Returns singleton instance for this class in this thread. If none exists, one is created.
+      def instance
+        current_instances[name] ||= new
+      end
+
+      # Declares one or more attributes that will be given both class and instance accessor methods.
+      def attribute(*names)
+        generated_attribute_methods.module_eval do
+          names.each do |name|
+            define_method(name) do
+              attributes[name.to_sym]
+            end
+
+            define_method("#{name}=") do |attribute|
+              attributes[name.to_sym] = attribute
+            end
+          end
+        end
+
+        names.each do |name|
+          define_singleton_method(name) do
+            instance.public_send(name)
+          end
+
+          define_singleton_method("#{name}=") do |attribute|
+            instance.public_send("#{name}=", attribute)
+          end
+        end
+      end
+
+      # Calls this block after #reset is called on the instance. Used for resetting external collaborators, like Time.zone.
+      def resets(&block)
+        set_callback :reset, :after, &block
+      end
+
+      delegate :set, :reset, to: :instance
+
+      def reset_all # :nodoc:
+        current_instances.each_value(&:reset)
+      end
+
+      def clear_all # :nodoc:
+        reset_all
+        current_instances.clear
+      end
+
+      private
+        def generated_attribute_methods
+          @generated_attribute_methods ||= Module.new.tap { |mod| include mod }
+        end
+
+        def current_instances
+          Thread.current[:current_attributes_instances] ||= {}
+        end
+
+        def method_missing(name, *args, &block)
+          # Caches the method definition as a singleton method of the receiver.
+          #
+          # By letting #delegate handle it, we avoid an enclosure that'll capture args.
+          singleton_class.delegate name, to: :instance
+
+          send(name, *args, &block)
+        end
+    end
+
+    attr_accessor :attributes
+
+    def initialize
+      @attributes = {}
+    end
+
+    # Expose one or more attributes within a block. Old values are returned after the block concludes.
+    # Example demonstrating the common use of needing to set Current attributes outside the request-cycle:
+    #
+    #   class Chat::PublicationJob < ApplicationJob
+    #     def perform(attributes, room_number, creator)
+    #       Current.set(person: creator) do
+    #         Chat::Publisher.publish(attributes: attributes, room_number: room_number)
+    #       end
+    #     end
+    #   end
+    def set(set_attributes)
+      old_attributes = compute_attributes(set_attributes.keys)
+      assign_attributes(set_attributes)
+      yield
+    ensure
+      assign_attributes(old_attributes)
+    end
+
+    # Reset all attributes. Should be called before and after actions, when used as a per-request singleton.
+    def reset
+      run_callbacks :reset do
+        self.attributes = {}
+      end
+    end
+
+    private
+      def assign_attributes(new_attributes)
+        new_attributes.each { |key, value| public_send("#{key}=", value) }
+      end
+
+      def compute_attributes(keys)
+        keys.collect { |key| [ key, public_send(key) ] }.to_h
+      end
+  end
+end
diff --git a/activesupport/lib/active_support/deprecation/reporting.rb b/activesupport/lib/active_support/deprecation/reporting.rb
index 851d8eeda1..140bdccbb3 100644
--- a/activesupport/lib/active_support/deprecation/reporting.rb
+++ b/activesupport/lib/active_support/deprecation/reporting.rb
@@ -102,7 +102,7 @@ module ActiveSupport
           end
         end
 
-        RAILS_GEM_ROOT = File.expand_path("../../../../..", __FILE__) + "/"
+        RAILS_GEM_ROOT = File.expand_path("../../../..", __dir__)
 
         def ignored_callstack(path)
           path.start_with?(RAILS_GEM_ROOT) || path.start_with?(RbConfig::CONFIG["rubylibdir"])
diff --git a/activesupport/lib/active_support/duration.rb b/activesupport/lib/active_support/duration.rb
index d4424ed792..39deb2313f 100644
--- a/activesupport/lib/active_support/duration.rb
+++ b/activesupport/lib/active_support/duration.rb
@@ -37,27 +37,56 @@ module ActiveSupport
       end
 
       def +(other)
-        calculate(:+, other)
+        if Duration === other
+          seconds   = value + other.parts[:seconds]
+          new_parts = other.parts.merge(seconds: seconds)
+          new_value = value + other.value
+
+          Duration.new(new_value, new_parts)
+        else
+          calculate(:+, other)
+        end
       end
 
       def -(other)
-        calculate(:-, other)
+        if Duration === other
+          seconds   = value - other.parts[:seconds]
+          new_parts = other.parts.map { |part, other_value| [part, -other_value] }.to_h
+          new_parts = new_parts.merge(seconds: seconds)
+          new_value = value - other.value
+
+          Duration.new(new_value, new_parts)
+        else
+          calculate(:-, other)
+        end
       end
 
       def *(other)
-        calculate(:*, other)
+        if Duration === other
+          new_parts = other.parts.map { |part, other_value| [part, value * other_value] }.to_h
+          new_value = value * other.value
+
+          Duration.new(new_value, new_parts)
+        else
+          calculate(:*, other)
+        end
       end
 
       def /(other)
-        calculate(:/, other)
+        if Duration === other
+          new_parts = other.parts.map { |part, other_value| [part, value / other_value] }.to_h
+          new_value = new_parts.inject(0) { |total, (part, value)| total + value * Duration::PARTS_IN_SECONDS[part] }
+
+          Duration.new(new_value, new_parts)
+        else
+          calculate(:/, other)
+        end
       end
 
       private
         def calculate(op, other)
           if Scalar === other
             Scalar.new(value.public_send(op, other.value))
-          elsif Duration === other
-            Duration.seconds(value).public_send(op, other)
           elsif Numeric === other
             Scalar.new(value.public_send(op, other))
           else
diff --git a/activesupport/lib/active_support/i18n.rb b/activesupport/lib/active_support/i18n.rb
index f0408f429c..1a1f1a1257 100644
--- a/activesupport/lib/active_support/i18n.rb
+++ b/activesupport/lib/active_support/i18n.rb
@@ -10,4 +10,4 @@ end
 require "active_support/lazy_load_hooks"
 
 ActiveSupport.run_load_hooks(:i18n)
-I18n.load_path << "#{File.dirname(__FILE__)}/locale/en.yml"
+I18n.load_path << File.expand_path("locale/en.yml", __dir__)
diff --git a/activesupport/lib/active_support/i18n_railtie.rb b/activesupport/lib/active_support/i18n_railtie.rb
index b749913ee9..51fe6f3418 100644
--- a/activesupport/lib/active_support/i18n_railtie.rb
+++ b/activesupport/lib/active_support/i18n_railtie.rb
@@ -42,7 +42,7 @@ module I18n
         case setting
         when :railties_load_path
           reloadable_paths = value
-          app.config.i18n.load_path.unshift(*value.map(&:existent).flatten)
+          app.config.i18n.load_path.unshift(*value.flat_map(&:existent))
         when :load_path
           I18n.load_path += value
         else
@@ -58,7 +58,7 @@ module I18n
       directories = watched_dirs_with_extensions(reloadable_paths)
       reloader = app.config.file_watcher.new(I18n.load_path.dup, directories) do
         I18n.load_path.keep_if { |p| File.exist?(p) }
-        I18n.load_path |= reloadable_paths.map(&:existent).flatten
+        I18n.load_path |= reloadable_paths.flat_map(&:existent)
 
         I18n.reload!
       end
@@ -66,10 +66,6 @@ module I18n
       app.reloaders << reloader
       app.reloader.to_run do
         reloader.execute_if_updated { require_unload_lock! }
-        # TODO: remove the following line as soon as the return value of
-        # callbacks is ignored, that is, returning `false` does not
-        # display a deprecation warning or halts the callback chain.
-        true
       end
       reloader.execute
 
diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index 1b089a7538..ff1a0cb8c7 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -28,7 +28,7 @@ module ActiveSupport
     #   pluralize('CamelOctopus')     # => "CamelOctopi"
     #   pluralize('ley', :es)         # => "leyes"
     def pluralize(word, locale = :en)
-      apply_inflections(word, inflections(locale).plurals)
+      apply_inflections(word, inflections(locale).plurals, locale)
     end
 
     # The reverse of #pluralize, returns the singular form of a word in a
@@ -45,7 +45,7 @@ module ActiveSupport
     #   singularize('CamelOctopi')      # => "CamelOctopus"
     #   singularize('leyes', :es)       # => "ley"
     def singularize(word, locale = :en)
-      apply_inflections(word, inflections(locale).singulars)
+      apply_inflections(word, inflections(locale).singulars, locale)
     end
 
     # Converts strings to UpperCamelCase.
@@ -387,12 +387,15 @@ module ActiveSupport
 
       # Applies inflection rules for +singularize+ and +pluralize+.
       #
-      #  apply_inflections('post', inflections.plurals)    # => "posts"
-      #  apply_inflections('posts', inflections.singulars) # => "post"
-      def apply_inflections(word, rules)
+      # If passed an optional +locale+ parameter, the uncountables will be
+      # found for that locale.
+      #
+      #  apply_inflections('post', inflections.plurals, :en)    # => "posts"
+      #  apply_inflections('posts', inflections.singulars, :en) # => "post"
+      def apply_inflections(word, rules, locale = :en)
         result = word.to_s.dup
 
-        if word.empty? || inflections.uncountables.uncountable?(result)
+        if word.empty? || inflections(locale).uncountables.uncountable?(result)
           result
         else
           rules.each { |(rule, replacement)| break if result.sub!(rule, replacement) }
diff --git a/activesupport/lib/active_support/message_encryptor.rb b/activesupport/lib/active_support/message_encryptor.rb
index 24053b4fe5..726e1464ad 100644
--- a/activesupport/lib/active_support/message_encryptor.rb
+++ b/activesupport/lib/active_support/message_encryptor.rb
@@ -115,7 +115,7 @@ module ActiveSupport
         # Currently the OpenSSL bindings do not raise an error if auth_tag is
         # truncated, which would allow an attacker to easily forge it. See
         # https://github.com/ruby/openssl/issues/63
-        raise InvalidMessage if aead_mode? && auth_tag.bytes.length != 16
+        raise InvalidMessage if aead_mode? && (auth_tag.nil? || auth_tag.bytes.length != 16)
 
         cipher.decrypt
         cipher.key = @secret
diff --git a/activesupport/lib/active_support/multibyte/unicode.rb b/activesupport/lib/active_support/multibyte/unicode.rb
index 0912912aba..8223e45e5a 100644
--- a/activesupport/lib/active_support/multibyte/unicode.rb
+++ b/activesupport/lib/active_support/multibyte/unicode.rb
@@ -357,7 +357,7 @@ module ActiveSupport
 
         # Returns the directory in which the data files are stored.
         def self.dirname
-          File.dirname(__FILE__) + "/../values/"
+          File.expand_path("../values", __dir__)
         end
 
         # Returns the filename for the data file for this version.
diff --git a/activesupport/lib/active_support/number_helper.rb b/activesupport/lib/active_support/number_helper.rb
index 880340ca86..9cb2821cb6 100644
--- a/activesupport/lib/active_support/number_helper.rb
+++ b/activesupport/lib/active_support/number_helper.rb
@@ -4,6 +4,7 @@ module ActiveSupport
 
     eager_autoload do
       autoload :NumberConverter
+      autoload :RoundingHelper
       autoload :NumberToRoundedConverter
       autoload :NumberToDelimitedConverter
       autoload :NumberToHumanConverter
diff --git a/activesupport/lib/active_support/number_helper/number_to_human_converter.rb b/activesupport/lib/active_support/number_helper/number_to_human_converter.rb
index 56185ddf4b..040343b5dd 100644
--- a/activesupport/lib/active_support/number_helper/number_to_human_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_human_converter.rb
@@ -9,6 +9,7 @@ module ActiveSupport
       self.validate_float = true
 
       def convert # :nodoc:
+        @number = RoundingHelper.new(options).round(number)
         @number = Float(number)
 
         # for backwards compatibility with those that didn't add strip_insignificant_zeros to their locale files
@@ -20,10 +21,7 @@ module ActiveSupport
         exponent = calculate_exponent(units)
         @number = number / (10**exponent)
 
-        until (rounded_number = NumberToRoundedConverter.convert(number, options)) != NumberToRoundedConverter.convert(1000, options)
-          @number = number / 1000.0
-          exponent += 3
-        end
+        rounded_number = NumberToRoundedConverter.convert(number, options)
         unit = determine_unit(units, exponent)
         format.gsub("%n".freeze, rounded_number).gsub("%u".freeze, unit).strip
       end
diff --git a/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
index 1f013990ea..c32d85a45f 100644
--- a/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
@@ -5,26 +5,14 @@ module ActiveSupport
       self.validate_float = true
 
       def convert
-        precision = options.delete :precision
+        helper = RoundingHelper.new(options)
+        rounded_number = helper.round(number)
 
-        if precision
-          case number
-          when Float, String
-            @number = BigDecimal(number.to_s)
-          when Rational
-            @number = BigDecimal(number, digit_count(number.to_i) + precision)
-          else
-            @number = number.to_d
-          end
-
-          if options.delete(:significant) && precision > 0
-            digits, rounded_number = digits_and_rounded_number(precision)
+        if precision = options[:precision]
+          if options[:significant] && precision > 0
+            digits = helper.digit_count(rounded_number)
             precision -= digits
             precision = 0 if precision < 0 # don't let it be negative
-          else
-            rounded_number = number.round(precision)
-            rounded_number = rounded_number.to_i if precision == 0 && rounded_number.finite?
-            rounded_number = rounded_number.abs if rounded_number.zero? # prevent showing negative zeros
           end
 
           formatted_string =
@@ -38,7 +26,7 @@ module ActiveSupport
               "%00.#{precision}f" % rounded_number
             end
         else
-          formatted_string = number
+          formatted_string = rounded_number
         end
 
         delimited_number = NumberToDelimitedConverter.convert(formatted_string, options)
@@ -79,14 +67,6 @@ module ActiveSupport
             number
           end
         end
-
-        def absolute_number(number)
-          number.respond_to?(:abs) ? number.abs : number.to_d.abs
-        end
-
-        def zero?
-          number.respond_to?(:zero?) ? number.zero? : number.to_d.zero?
-        end
     end
   end
 end
diff --git a/activesupport/lib/active_support/number_helper/rounding_helper.rb b/activesupport/lib/active_support/number_helper/rounding_helper.rb
new file mode 100644
index 0000000000..d9644df17d
--- /dev/null
+++ b/activesupport/lib/active_support/number_helper/rounding_helper.rb
@@ -0,0 +1,64 @@
+module ActiveSupport
+  module NumberHelper
+    class RoundingHelper # :nodoc:
+      attr_reader :options
+
+      def initialize(options)
+        @options = options
+      end
+
+      def round(number)
+        return number unless precision
+        number = convert_to_decimal(number)
+        if significant && precision > 0
+          round_significant(number)
+        else
+          round_without_significant(number)
+        end
+      end
+
+      def digit_count(number)
+        return 1 if number.zero?
+        (Math.log10(absolute_number(number)) + 1).floor
+      end
+
+      private
+        def round_without_significant(number)
+          number = number.round(precision)
+          number = number.to_i if precision == 0 && number.finite?
+          number = number.abs if number.zero? # prevent showing negative zeros
+          number
+        end
+
+        def round_significant(number)
+          return 0 if number.zero?
+          digits = digit_count(number)
+          multiplier = 10**(digits - precision)
+          (number / BigDecimal.new(multiplier.to_f.to_s)).round * multiplier
+        end
+
+        def convert_to_decimal(number)
+          case number
+          when Float, String
+            number = BigDecimal(number.to_s)
+          when Rational
+            number = BigDecimal(number, digit_count(number.to_i) + precision)
+          else
+            number = number.to_d
+          end
+        end
+
+        def precision
+          options[:precision]
+        end
+
+        def significant
+          options[:significant]
+        end
+
+        def absolute_number(number)
+          number.respond_to?(:abs) ? number.abs : number.to_d.abs
+        end
+    end
+  end
+end
diff --git a/activesupport/lib/active_support/railtie.rb b/activesupport/lib/active_support/railtie.rb
index b875875afe..1b4ecf4d72 100644
--- a/activesupport/lib/active_support/railtie.rb
+++ b/activesupport/lib/active_support/railtie.rb
@@ -7,6 +7,12 @@ module ActiveSupport
 
     config.eager_load_namespaces << ActiveSupport
 
+    initializer "active_support.reset_all_current_attributes_instances" do |app|
+      app.reloader.before_class_unload { ActiveSupport::CurrentAttributes.clear_all }
+      app.executor.to_run              { ActiveSupport::CurrentAttributes.reset_all }
+      app.executor.to_complete         { ActiveSupport::CurrentAttributes.reset_all }
+    end
+
     initializer "active_support.deprecation_behavior" do |app|
       if deprecation = app.config.active_support.deprecation
         ActiveSupport::Deprecation.behavior = deprecation
diff --git a/activesupport/lib/active_support/reloader.rb b/activesupport/lib/active_support/reloader.rb
index 121c621751..9558146201 100644
--- a/activesupport/lib/active_support/reloader.rb
+++ b/activesupport/lib/active_support/reloader.rb
@@ -69,11 +69,8 @@ module ActiveSupport
       end
     end
 
-    class_attribute :executor
-    class_attribute :check
-
-    self.executor = Executor
-    self.check = lambda { false }
+    class_attribute :executor, default: Executor
+    class_attribute :check, default: lambda { false }
 
     def self.check! # :nodoc:
       @should_reload ||= check.call
diff --git a/activesupport/lib/active_support/rescuable.rb b/activesupport/lib/active_support/rescuable.rb
index ee6592fb5a..826832ba7d 100644
--- a/activesupport/lib/active_support/rescuable.rb
+++ b/activesupport/lib/active_support/rescuable.rb
@@ -8,8 +8,7 @@ module ActiveSupport
     extend Concern
 
     included do
-      class_attribute :rescue_handlers
-      self.rescue_handlers = []
+      class_attribute :rescue_handlers, default: []
     end
 
     module ClassMethods
@@ -84,12 +83,18 @@ module ActiveSupport
       #     end
       #
       # Returns the exception if it was handled and +nil+ if it was not.
-      def rescue_with_handler(exception, object: self)
+      def rescue_with_handler(exception, object: self, visited_exceptions: [])
+        visited_exceptions << exception
+
         if handler = handler_for_rescue(exception, object: object)
           handler.call exception
           exception
         elsif exception
-          rescue_with_handler(exception.cause, object: object)
+          if visited_exceptions.include?(exception.cause)
+            nil
+          else
+            rescue_with_handler(exception.cause, object: object, visited_exceptions: visited_exceptions)
+          end
         end
       end