Merge branch 'master' into feature/reselect-method

50 files changed, 295 insertions, 102 deletions

diff --git a/activesupport/lib/active_support/backtrace_cleaner.rb b/activesupport/lib/active_support/backtrace_cleaner.rb
index 16dd733ddb..62973eca58 100644
--- a/activesupport/lib/active_support/backtrace_cleaner.rb
+++ b/activesupport/lib/active_support/backtrace_cleaner.rb
@@ -31,6 +31,9 @@ module ActiveSupport
   class BacktraceCleaner
     def initialize
       @filters, @silencers = [], []
+      add_gem_filter
+      add_gem_silencer
+      add_stdlib_silencer
     end
 
     # Returns the backtrace after all filters and silencers have been run
@@ -82,6 +85,26 @@ module ActiveSupport
     end
 
     private
+
+      FORMATTED_GEMS_PATTERN = /\A[^\/]+ \([\w.]+\) /
+
+      def add_gem_filter
+        gems_paths = (Gem.path | [Gem.default_dir]).map { |p| Regexp.escape(p) }
+        return if gems_paths.empty?
+
+        gems_regexp = %r{(#{gems_paths.join('|')})/(bundler/)?gems/([^/]+)-([\w.]+)/(.*)}
+        gems_result = '\3 (\4) \5'
+        add_filter { |line| line.sub(gems_regexp, gems_result) }
+      end
+
+      def add_gem_silencer
+        add_silencer { |line| FORMATTED_GEMS_PATTERN.match?(line) }
+      end
+
+      def add_stdlib_silencer
+        add_silencer { |line| line.start_with?(RbConfig::CONFIG["rubylibdir"]) }
+      end
+
       def filter_backtrace(backtrace)
         @filters.each do |f|
           backtrace = backtrace.map { |line| f.call(line) }
diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb
index 8e516de4c9..a5d0c52b13 100644
--- a/activesupport/lib/active_support/cache.rb
+++ b/activesupport/lib/active_support/cache.rb
@@ -694,7 +694,7 @@ module ActiveSupport
         end
 
         def get_entry_value(entry, name, options)
-          instrument(:fetch_hit, name, options) {}
+          instrument(:fetch_hit, name, options) { }
           entry.value
         end
 
diff --git a/activesupport/lib/active_support/cache/file_store.rb b/activesupport/lib/active_support/cache/file_store.rb
index a0f44aac0f..53a2b07536 100644
--- a/activesupport/lib/active_support/cache/file_store.rb
+++ b/activesupport/lib/active_support/cache/file_store.rb
@@ -26,6 +26,11 @@ module ActiveSupport
         @cache_path = cache_path.to_s
       end
 
+      # Advertise cache versioning support.
+      def self.supports_cache_versioning?
+        true
+      end
+
       # Deletes all items from the cache. In this case it deletes all the entries in the specified
       # file store directory except for .keep or .gitkeep. Be careful which directory is specified in your
       # config file when using +FileStore+ because everything in that directory will be deleted.
@@ -127,15 +132,19 @@ module ActiveSupport
           hash = Zlib.adler32(fname)
           hash, dir_1 = hash.divmod(0x1000)
           dir_2 = hash.modulo(0x1000)
-          fname_paths = []
 
           # Make sure file name doesn't exceed file system limits.
-          begin
-            fname_paths << fname[0, FILENAME_MAX_SIZE]
-            fname = fname[FILENAME_MAX_SIZE..-1]
-          end until fname.blank?
+          if fname.length < FILENAME_MAX_SIZE
+            fname_paths = fname
+          else
+            fname_paths = []
+            begin
+              fname_paths << fname[0, FILENAME_MAX_SIZE]
+              fname = fname[FILENAME_MAX_SIZE..-1]
+            end until fname.blank?
+          end
 
-          File.join(cache_path, DIR_FORMATTER % dir_1, DIR_FORMATTER % dir_2, *fname_paths)
+          File.join(cache_path, DIR_FORMATTER % dir_1, DIR_FORMATTER % dir_2, fname_paths)
         end
 
         # Translate a file path into a key.
diff --git a/activesupport/lib/active_support/cache/mem_cache_store.rb b/activesupport/lib/active_support/cache/mem_cache_store.rb
index 2840781dde..174c784deb 100644
--- a/activesupport/lib/active_support/cache/mem_cache_store.rb
+++ b/activesupport/lib/active_support/cache/mem_cache_store.rb
@@ -47,6 +47,11 @@ module ActiveSupport
           end
       end
 
+      # Advertise cache versioning support.
+      def self.supports_cache_versioning?
+        true
+      end
+
       prepend Strategy::LocalCache
       prepend LocalCacheWithRaw
 
diff --git a/activesupport/lib/active_support/cache/memory_store.rb b/activesupport/lib/active_support/cache/memory_store.rb
index 564ac17241..106b616529 100644
--- a/activesupport/lib/active_support/cache/memory_store.rb
+++ b/activesupport/lib/active_support/cache/memory_store.rb
@@ -30,6 +30,11 @@ module ActiveSupport
         @pruning = false
       end
 
+      # Advertise cache versioning support.
+      def self.supports_cache_versioning?
+        true
+      end
+
       # Delete all data stored in a given cache store.
       def clear(options = nil)
         synchronize do
diff --git a/activesupport/lib/active_support/cache/null_store.rb b/activesupport/lib/active_support/cache/null_store.rb
index 1a5983db43..8452a28fd8 100644
--- a/activesupport/lib/active_support/cache/null_store.rb
+++ b/activesupport/lib/active_support/cache/null_store.rb
@@ -12,6 +12,11 @@ module ActiveSupport
     class NullStore < Store
       prepend Strategy::LocalCache
 
+      # Advertise cache versioning support.
+      def self.supports_cache_versioning?
+        true
+      end
+
       def clear(options = nil)
       end
 
diff --git a/activesupport/lib/active_support/cache/redis_cache_store.rb b/activesupport/lib/active_support/cache/redis_cache_store.rb
index 5737450b4a..9a55e49e27 100644
--- a/activesupport/lib/active_support/cache/redis_cache_store.rb
+++ b/activesupport/lib/active_support/cache/redis_cache_store.rb
@@ -66,6 +66,11 @@ module ActiveSupport
       SCAN_BATCH_SIZE = 1000
       private_constant :SCAN_BATCH_SIZE
 
+      # Advertise cache versioning support.
+      def self.supports_cache_versioning?
+        true
+      end
+
       # Support raw values in the local cache strategy.
       module LocalCacheWithRaw # :nodoc:
         private
diff --git a/activesupport/lib/active_support/callbacks.rb b/activesupport/lib/active_support/callbacks.rb
index c266b432c0..487fe79f41 100644
--- a/activesupport/lib/active_support/callbacks.rb
+++ b/activesupport/lib/active_support/callbacks.rb
@@ -657,9 +657,17 @@ module ActiveSupport
         # * <tt>:if</tt> - A symbol or an array of symbols, each naming an instance
         #   method or a proc; the callback will be called only when they all return
         #   a true value.
+        #
+        #   If a proc is given, its body is evaluated in the context of the
+        #   current object. It can also optionally accept the current object as
+        #   an argument.
         # * <tt>:unless</tt> - A symbol or an array of symbols, each naming an
         #   instance method or a proc; the callback will be called only when they
         #   all return a false value.
+        #
+        #   If a proc is given, its body is evaluated in the context of the
+        #   current object. It can also optionally accept the current object as
+        #   an argument.
         # * <tt>:prepend</tt> - If +true+, the callback will be prepended to the
         #   existing chain rather than appended.
         def set_callback(name, *filter_list, &block)
diff --git a/activesupport/lib/active_support/core_ext/array.rb b/activesupport/lib/active_support/core_ext/array.rb
index 6d83b76882..a2569c798b 100644
--- a/activesupport/lib/active_support/core_ext/array.rb
+++ b/activesupport/lib/active_support/core_ext/array.rb
@@ -3,6 +3,7 @@
 require "active_support/core_ext/array/wrap"
 require "active_support/core_ext/array/access"
 require "active_support/core_ext/array/conversions"
+require "active_support/core_ext/array/extract"
 require "active_support/core_ext/array/extract_options"
 require "active_support/core_ext/array/grouping"
 require "active_support/core_ext/array/prepend_and_append"
diff --git a/activesupport/lib/active_support/core_ext/array/extract.rb b/activesupport/lib/active_support/core_ext/array/extract.rb
new file mode 100644
index 0000000000..cc5a8a3f88
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/array/extract.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class Array
+  # Removes and returns the elements for which the block returns a true value.
+  # If no block is given, an Enumerator is returned instead.
+  #
+  #   numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+  #   odd_numbers = numbers.extract! { |number| number.odd? } # => [1, 3, 5, 7, 9]
+  #   numbers # => [0, 2, 4, 6, 8]
+  def extract!
+    return to_enum(:extract!) { size } unless block_given?
+
+    extracted_elements = []
+
+    reject! do |element|
+      extracted_elements << element if yield(element)
+    end
+
+    extracted_elements
+  end
+end
diff --git a/activesupport/lib/active_support/core_ext/class/subclasses.rb b/activesupport/lib/active_support/core_ext/class/subclasses.rb
index 75e65337b7..56fb46a88d 100644
--- a/activesupport/lib/active_support/core_ext/class/subclasses.rb
+++ b/activesupport/lib/active_support/core_ext/class/subclasses.rb
@@ -3,7 +3,7 @@
 class Class
   begin
     # Test if this Ruby supports each_object against singleton_class
-    ObjectSpace.each_object(Numeric.singleton_class) {}
+    ObjectSpace.each_object(Numeric.singleton_class) { }
 
     # Returns an array with all classes that are < than its receiver.
     #
diff --git a/activesupport/lib/active_support/core_ext/integer/multiple.rb b/activesupport/lib/active_support/core_ext/integer/multiple.rb
index e7606662d3..bd57a909c5 100644
--- a/activesupport/lib/active_support/core_ext/integer/multiple.rb
+++ b/activesupport/lib/active_support/core_ext/integer/multiple.rb
@@ -7,6 +7,6 @@ class Integer
   #   6.multiple_of?(5)  # => false
   #   10.multiple_of?(2) # => true
   def multiple_of?(number)
-    number != 0 ? self % number == 0 : zero?
+    number == 0 ? self == 0 : self % number == 0
   end
 end
diff --git a/activesupport/lib/active_support/core_ext/load_error.rb b/activesupport/lib/active_support/core_ext/load_error.rb
index 6b0dcab905..b81ed0605e 100644
--- a/activesupport/lib/active_support/core_ext/load_error.rb
+++ b/activesupport/lib/active_support/core_ext/load_error.rb
@@ -4,6 +4,6 @@ class LoadError
   # Returns true if the given path name (except perhaps for the ".rb"
   # extension) is the missing file which caused the exception to be raised.
   def is_missing?(location)
-    location.sub(/\.rb$/, "".freeze) == path.to_s.sub(/\.rb$/, "".freeze)
+    location.sub(/\.rb$/, "") == path.to_s.sub(/\.rb$/, "")
   end
 end
diff --git a/activesupport/lib/active_support/core_ext/object/blank.rb b/activesupport/lib/active_support/core_ext/object/blank.rb
index ad6a9c6146..f36fef6cc9 100644
--- a/activesupport/lib/active_support/core_ext/object/blank.rb
+++ b/activesupport/lib/active_support/core_ext/object/blank.rb
@@ -4,7 +4,7 @@ require "concurrent/map"
 
 class Object
   # An object is blank if it's false, empty, or a whitespace string.
-  # For example, +false+, '', '   ', +nil+, [], and {} are all blank.
+  # For example, +nil+, '', '   ', [], {}, and +false+ are all blank.
   #
   # This simplifies
   #
diff --git a/activesupport/lib/active_support/core_ext/object/try.rb b/activesupport/lib/active_support/core_ext/object/try.rb
index c874691629..aa6896af32 100644
--- a/activesupport/lib/active_support/core_ext/object/try.rb
+++ b/activesupport/lib/active_support/core_ext/object/try.rb
@@ -4,19 +4,27 @@ require "delegate"
 
 module ActiveSupport
   module Tryable #:nodoc:
-    def try(*a, &b)
-      try!(*a, &b) if a.empty? || respond_to?(a.first)
+    def try(method_name = nil, *args, &b)
+      if method_name.nil? && block_given?
+        if b.arity == 0
+          instance_eval(&b)
+        else
+          yield self
+        end
+      elsif respond_to?(method_name)
+        public_send(method_name, *args, &b)
+      end
     end
 
-    def try!(*a, &b)
-      if a.empty? && block_given?
+    def try!(method_name = nil, *args, &b)
+      if method_name.nil? && block_given?
         if b.arity == 0
           instance_eval(&b)
         else
           yield self
         end
       else
-        public_send(*a, &b)
+        public_send(method_name, *args, &b)
       end
     end
   end
diff --git a/activesupport/lib/active_support/core_ext/string/access.rb b/activesupport/lib/active_support/core_ext/string/access.rb
index 58591bbaaf..4ca24028b0 100644
--- a/activesupport/lib/active_support/core_ext/string/access.rb
+++ b/activesupport/lib/active_support/core_ext/string/access.rb
@@ -75,6 +75,10 @@ class String
   #   str.first(0) # => ""
   #   str.first(6) # => "hello"
   def first(limit = 1)
+    ActiveSupport::Deprecation.warn(
+      "Calling String#first with a negative integer limit " \
+      "will raise an ArgumentError in Rails 6.1."
+    ) if limit < 0
     if limit == 0
       ""
     elsif limit >= size
@@ -95,6 +99,10 @@ class String
   #   str.last(0) # => ""
   #   str.last(6) # => "hello"
   def last(limit = 1)
+    ActiveSupport::Deprecation.warn(
+      "Calling String#last with a negative integer limit " \
+      "will raise an ArgumentError in Rails 6.1."
+    ) if limit < 0
     if limit == 0
       ""
     elsif limit >= size
diff --git a/activesupport/lib/active_support/core_ext/string/output_safety.rb b/activesupport/lib/active_support/core_ext/string/output_safety.rb
index f3bdc2977e..3a80de4617 100644
--- a/activesupport/lib/active_support/core_ext/string/output_safety.rb
+++ b/activesupport/lib/active_support/core_ext/string/output_safety.rb
@@ -134,8 +134,9 @@ end
 module ActiveSupport #:nodoc:
   class SafeBuffer < String
     UNSAFE_STRING_METHODS = %w(
-      capitalize chomp chop delete downcase gsub lstrip next reverse rstrip
-      slice squeeze strip sub succ swapcase tr tr_s upcase
+      capitalize chomp chop delete delete_prefix delete_suffix
+      downcase gsub lstrip next reverse rstrip slice squeeze strip
+      sub succ swapcase tr tr_s unicode_normalize upcase
     )
 
     alias_method :original_concat, :concat
@@ -149,9 +150,7 @@ module ActiveSupport #:nodoc:
     end
 
     def [](*args)
-      if args.size < 2
-        super
-      elsif html_safe?
+      if html_safe?
         new_safe_buffer = super
 
         if new_safe_buffer
@@ -188,10 +187,22 @@ module ActiveSupport #:nodoc:
     end
     alias << concat
 
+    def insert(index, value)
+      super(index, html_escape_interpolated_argument(value))
+    end
+
     def prepend(value)
       super(html_escape_interpolated_argument(value))
     end
 
+    def replace(value)
+      super(html_escape_interpolated_argument(value))
+    end
+
+    def []=(index, value)
+      super(index, html_escape_interpolated_argument(value))
+    end
+
     def +(other)
       dup.concat(other)
     end
diff --git a/activesupport/lib/active_support/core_ext/string/strip.rb b/activesupport/lib/active_support/core_ext/string/strip.rb
index 6f9834bb16..60e9952ee6 100644
--- a/activesupport/lib/active_support/core_ext/string/strip.rb
+++ b/activesupport/lib/active_support/core_ext/string/strip.rb
@@ -20,7 +20,7 @@ class String
   # Technically, it looks for the least indented non-empty line
   # in the whole string, and removes that amount of leading whitespace.
   def strip_heredoc
-    gsub(/^#{scan(/^[ \t]*(?=\S)/).min}/, "".freeze).tap do |stripped|
+    gsub(/^#{scan(/^[ \t]*(?=\S)/).min}/, "").tap do |stripped|
       stripped.freeze if frozen?
     end
   end
diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index 9dc2c46880..063d8d1587 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -79,6 +79,12 @@ module ActiveSupport #:nodoc:
     # to allow arbitrary constants to be marked for unloading.
     mattr_accessor :explicitly_unloadable_constants, default: []
 
+    # The logger used when tracing autoloads.
+    mattr_accessor :logger
+
+    # If true, trace autoloads with +logger.debug+.
+    mattr_accessor :verbose, default: false
+
     # The WatchStack keeps a stack of the modules being watched as files are
     # loaded. If a file in the process of being loaded (parent.rb) triggers the
     # load of another file (child.rb) the stack will ensure that child.rb
@@ -138,7 +144,7 @@ module ActiveSupport #:nodoc:
 
           # Normalize the list of new constants, and add them to the list we will return
           new_constants.each do |suffix|
-            constants << ([namespace, suffix] - ["Object"]).join("::".freeze)
+            constants << ([namespace, suffix] - ["Object"]).join("::")
           end
         end
         constants
@@ -404,7 +410,7 @@ module ActiveSupport #:nodoc:
         next unless expanded_path.start_with?(expanded_root)
 
         root_size = expanded_root.size
-        next if expanded_path[root_size] != ?/.freeze
+        next if expanded_path[root_size] != ?/
 
         nesting = expanded_path[(root_size + 1)..-1]
         paths << nesting.camelize unless nesting.blank?
@@ -416,7 +422,7 @@ module ActiveSupport #:nodoc:
 
     # Search for a file in autoload_paths matching the provided suffix.
     def search_for_file(path_suffix)
-      path_suffix = path_suffix.sub(/(\.rb)?$/, ".rb".freeze)
+      path_suffix += ".rb" unless path_suffix.ends_with?(".rb")
 
       autoload_paths.each do |root|
         path = File.join(root, path_suffix)
@@ -450,6 +456,7 @@ module ActiveSupport #:nodoc:
       return nil unless base_path = autoloadable_module?(path_suffix)
       mod = Module.new
       into.const_set const_name, mod
+      log("constant #{qualified_name} autoloaded (module autovivified from #{File.join(base_path, path_suffix)})")
       autoloaded_constants << qualified_name unless autoload_once_paths.include?(base_path)
       autoloaded_constants.uniq!
       mod
@@ -491,21 +498,26 @@ module ActiveSupport #:nodoc:
         raise ArgumentError, "A copy of #{from_mod} has been removed from the module tree but is still active!"
       end
 
-      qualified_name = qualified_name_for from_mod, const_name
+      qualified_name = qualified_name_for(from_mod, const_name)
       path_suffix = qualified_name.underscore
 
       file_path = search_for_file(path_suffix)
 
       if file_path
         expanded = File.expand_path(file_path)
-        expanded.sub!(/\.rb\z/, "".freeze)
+        expanded.sub!(/\.rb\z/, "")
 
         if loading.include?(expanded)
           raise "Circular dependency detected while autoloading constant #{qualified_name}"
         else
           require_or_load(expanded, qualified_name)
-          raise LoadError, "Unable to autoload constant #{qualified_name}, expected #{file_path} to define it" unless from_mod.const_defined?(const_name, false)
-          return from_mod.const_get(const_name)
+
+          if from_mod.const_defined?(const_name, false)
+            log("constant #{qualified_name} autoloaded from #{expanded}.rb")
+            return from_mod.const_get(const_name)
+          else
+            raise LoadError, "Unable to autoload constant #{qualified_name}, expected #{file_path} to define it"
+          end
         end
       elsif mod = autoload_module!(from_mod, const_name, qualified_name, path_suffix)
         return mod
@@ -554,6 +566,7 @@ module ActiveSupport #:nodoc:
     # as the environment will be in an inconsistent state, e.g. other constants
     # may have already been unloaded and not accessible.
     def remove_unloadable_constants!
+      log("removing unloadable constants")
       autoloaded_constants.each { |const| remove_constant const }
       autoloaded_constants.clear
       Reference.clear!
@@ -743,6 +756,10 @@ module ActiveSupport #:nodoc:
         # The constant is no longer reachable, just skip it.
       end
     end
+
+    def log(message)
+      logger.debug("autoloading: #{message}") if logger && verbose
+    end
   end
 end
 
diff --git a/activesupport/lib/active_support/deprecation/behaviors.rb b/activesupport/lib/active_support/deprecation/behaviors.rb
index 3abd25aa85..725667d139 100644
--- a/activesupport/lib/active_support/deprecation/behaviors.rb
+++ b/activesupport/lib/active_support/deprecation/behaviors.rb
@@ -43,7 +43,7 @@ module ActiveSupport
                                                 deprecation_horizon: deprecation_horizon)
       },
 
-      silence: ->(message, callstack, deprecation_horizon, gem_name) {},
+      silence: ->(message, callstack, deprecation_horizon, gem_name) { },
     }
 
     # Behavior module allows to determine how to display deprecation messages.
diff --git a/activesupport/lib/active_support/duration/iso8601_parser.rb b/activesupport/lib/active_support/duration/iso8601_parser.rb
index 414f727705..d3233e6111 100644
--- a/activesupport/lib/active_support/duration/iso8601_parser.rb
+++ b/activesupport/lib/active_support/duration/iso8601_parser.rb
@@ -13,8 +13,8 @@ module ActiveSupport
       class ParsingError < ::ArgumentError; end
 
       PERIOD_OR_COMMA = /\.|,/
-      PERIOD = ".".freeze
-      COMMA = ",".freeze
+      PERIOD = "."
+      COMMA = ","
 
       SIGN_MARKER = /\A\-|\+|/
       DATE_MARKER = /P/
diff --git a/activesupport/lib/active_support/duration/iso8601_serializer.rb b/activesupport/lib/active_support/duration/iso8601_serializer.rb
index 84ae29c1ec..1125454919 100644
--- a/activesupport/lib/active_support/duration/iso8601_serializer.rb
+++ b/activesupport/lib/active_support/duration/iso8601_serializer.rb
@@ -14,14 +14,14 @@ module ActiveSupport
       # Builds and returns output string.
       def serialize
         parts, sign = normalize
-        return "PT0S".freeze if parts.empty?
+        return "PT0S" if parts.empty?
 
-        output = "P".dup
+        output = +"P"
         output << "#{parts[:years]}Y"   if parts.key?(:years)
         output << "#{parts[:months]}M"  if parts.key?(:months)
         output << "#{parts[:weeks]}W"   if parts.key?(:weeks)
         output << "#{parts[:days]}D"    if parts.key?(:days)
-        time = "".dup
+        time = +""
         time << "#{parts[:hours]}H"     if parts.key?(:hours)
         time << "#{parts[:minutes]}M"   if parts.key?(:minutes)
         if parts.key?(:seconds)
diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index e4afc8af93..2fac579469 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -2,6 +2,7 @@
 
 require "active_support/core_ext/hash/keys"
 require "active_support/core_ext/hash/reverse_merge"
+require "active_support/core_ext/hash/except"
 
 module ActiveSupport
   # Implements a hash where keys <tt>:foo</tt> and <tt>"foo"</tt> are considered
@@ -279,6 +280,8 @@ module ActiveSupport
       super(convert_key(key))
     end
 
+    alias_method :without, :except
+
     def stringify_keys!; self end
     def deep_stringify_keys!; self end
     def stringify_keys; dup end
diff --git a/activesupport/lib/active_support/i18n_railtie.rb b/activesupport/lib/active_support/i18n_railtie.rb
index 93bde57f6a..584930e413 100644
--- a/activesupport/lib/active_support/i18n_railtie.rb
+++ b/activesupport/lib/active_support/i18n_railtie.rb
@@ -87,9 +87,21 @@ module I18n
         when Hash, Array
           Array.wrap(fallbacks)
         else # TrueClass
-          []
+          [I18n.default_locale]
         end
 
+      if args.empty? || args.first.is_a?(Hash)
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          Using I18n fallbacks with an empty `defaults` sets the defaults to
+          include the `default_locale`. This behavior will change in Rails 6.1.
+          If you desire the default locale to be included in the defaults, please
+          explicitly configure it with `config.i18n.fallbacks.defaults =
+          [I18n.default_locale]` or `config.i18n.fallbacks = [I18n.default_locale,
+          {...}]`
+        MSG
+        args.unshift I18n.default_locale
+      end
+
       I18n.fallbacks = I18n::Locale::Fallbacks.new(*args)
     end
 
diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index 7359de762a..1af9833d46 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -73,7 +73,7 @@ module ActiveSupport
         string = string.sub(inflections.acronyms_camelize_regex) { |match| match.downcase }
       end
       string.gsub!(/(?:_|(\/))([a-z\d]*)/i) { "#{$1}#{inflections.acronyms[$2] || $2.capitalize}" }
-      string.gsub!("/".freeze, "::".freeze)
+      string.gsub!("/", "::")
       string
     end
 
@@ -90,11 +90,11 @@ module ActiveSupport
     #   camelize(underscore('SSLError'))  # => "SslError"
     def underscore(camel_cased_word)
       return camel_cased_word unless /[A-Z-]|::/.match?(camel_cased_word)
-      word = camel_cased_word.to_s.gsub("::".freeze, "/".freeze)
-      word.gsub!(inflections.acronyms_underscore_regex) { "#{$1 && '_'.freeze }#{$2.downcase}" }
-      word.gsub!(/([A-Z\d]+)([A-Z][a-z])/, '\1_\2'.freeze)
-      word.gsub!(/([a-z\d])([A-Z])/, '\1_\2'.freeze)
-      word.tr!("-".freeze, "_".freeze)
+      word = camel_cased_word.to_s.gsub("::", "/")
+      word.gsub!(inflections.acronyms_underscore_regex) { "#{$1 && '_' }#{$2.downcase}" }
+      word.gsub!(/([A-Z\d]+)([A-Z][a-z])/, '\1_\2')
+      word.gsub!(/([a-z\d])([A-Z])/, '\1_\2')
+      word.tr!("-", "_")
       word.downcase!
       word
     end
@@ -130,11 +130,11 @@ module ActiveSupport
 
       inflections.humans.each { |(rule, replacement)| break if result.sub!(rule, replacement) }
 
-      result.sub!(/\A_+/, "".freeze)
+      result.sub!(/\A_+/, "")
       unless keep_id_suffix
-        result.sub!(/_id\z/, "".freeze)
+        result.sub!(/_id\z/, "")
       end
-      result.tr!("_".freeze, " ".freeze)
+      result.tr!("_", " ")
 
       result.gsub!(/([a-z\d]*)/i) do |match|
         "#{inflections.acronyms[match.downcase] || match.downcase}"
@@ -199,14 +199,14 @@ module ActiveSupport
     #   classify('calculus')     # => "Calculus"
     def classify(table_name)
       # strip out any leading schema name
-      camelize(singularize(table_name.to_s.sub(/.*\./, "".freeze)))
+      camelize(singularize(table_name.to_s.sub(/.*\./, "")))
     end
 
     # Replaces underscores with dashes in the string.
     #
     #   dasherize('puni_puni') # => "puni-puni"
     def dasherize(underscored_word)
-      underscored_word.tr("_".freeze, "-".freeze)
+      underscored_word.tr("_", "-")
     end
 
     # Removes the module part from the expression in the string.
@@ -269,7 +269,7 @@ module ActiveSupport
     # NameError is raised when the name is not in CamelCase or the constant is
     # unknown.
     def constantize(camel_cased_word)
-      names = camel_cased_word.split("::".freeze)
+      names = camel_cased_word.split("::")
 
       # Trigger a built-in NameError exception including the ill-formed constant in the message.
       Object.const_get(camel_cased_word) if names.empty?
@@ -364,7 +364,7 @@ module ActiveSupport
       #   const_regexp("Foo::Bar::Baz") # => "Foo(::Bar(::Baz)?)?"
       #   const_regexp("::")            # => "::"
       def const_regexp(camel_cased_word)
-        parts = camel_cased_word.split("::".freeze)
+        parts = camel_cased_word.split("::")
 
         return Regexp.escape(camel_cased_word) if parts.blank?
 
diff --git a/activesupport/lib/active_support/inflector/transliterate.rb b/activesupport/lib/active_support/inflector/transliterate.rb
index 6f2ca4999c..dbc8b8a2fa 100644
--- a/activesupport/lib/active_support/inflector/transliterate.rb
+++ b/activesupport/lib/active_support/inflector/transliterate.rb
@@ -58,7 +58,7 @@ module ActiveSupport
     #   I18n.locale = :de
     #   transliterate('Jürgen')
     #   # => "Juergen"
-    def transliterate(string, replacement = "?".freeze)
+    def transliterate(string, replacement = "?")
       raise ArgumentError, "Can only transliterate strings. Received #{string.class.name}" unless string.is_a?(String)
 
       I18n.transliterate(
@@ -97,7 +97,7 @@ module ActiveSupport
       parameterized_string.gsub!(/[^a-z0-9\-_]+/i, separator)
 
       unless separator.nil? || separator.empty?
-        if separator == "-".freeze
+        if separator == "-"
           re_duplicate_separator        = /-{2,}/
           re_leading_trailing_separator = /^-|-$/i
         else
@@ -108,7 +108,7 @@ module ActiveSupport
         # No more than one of the separator in a row.
         parameterized_string.gsub!(re_duplicate_separator, separator)
         # Remove leading/trailing separator.
-        parameterized_string.gsub!(re_leading_trailing_separator, "".freeze)
+        parameterized_string.gsub!(re_leading_trailing_separator, "")
       end
 
       parameterized_string.downcase! unless preserve_case
diff --git a/activesupport/lib/active_support/logger_silence.rb b/activesupport/lib/active_support/logger_silence.rb
index 89f32b6782..4344ca0429 100644
--- a/activesupport/lib/active_support/logger_silence.rb
+++ b/activesupport/lib/active_support/logger_silence.rb
@@ -2,7 +2,6 @@
 
 require "active_support/concern"
 require "active_support/core_ext/module/attribute_accessors"
-require "concurrent"
 
 module LoggerSilence
   extend ActiveSupport::Concern
diff --git a/activesupport/lib/active_support/logger_thread_safe_level.rb b/activesupport/lib/active_support/logger_thread_safe_level.rb
index ba32813d3d..22ab4cc28c 100644
--- a/activesupport/lib/active_support/logger_thread_safe_level.rb
+++ b/activesupport/lib/active_support/logger_thread_safe_level.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "active_support/concern"
+require "concurrent"
 
 module ActiveSupport
   module LoggerThreadSafeLevel # :nodoc:
diff --git a/activesupport/lib/active_support/message_encryptor.rb b/activesupport/lib/active_support/message_encryptor.rb
index 404404cad1..6f7302e732 100644
--- a/activesupport/lib/active_support/message_encryptor.rb
+++ b/activesupport/lib/active_support/message_encryptor.rb
@@ -182,7 +182,7 @@ module ActiveSupport
 
       def _decrypt(encrypted_message, purpose)
         cipher = new_cipher
-        encrypted_data, iv, auth_tag = encrypted_message.split("--".freeze).map { |v| ::Base64.strict_decode64(v) }
+        encrypted_data, iv, auth_tag = encrypted_message.split("--").map { |v| ::Base64.strict_decode64(v) }
 
         # Currently the OpenSSL bindings do not raise an error if auth_tag is
         # truncated, which would allow an attacker to easily forge it. See
diff --git a/activesupport/lib/active_support/message_verifier.rb b/activesupport/lib/active_support/message_verifier.rb
index 83c39c0a86..64c557bec6 100644
--- a/activesupport/lib/active_support/message_verifier.rb
+++ b/activesupport/lib/active_support/message_verifier.rb
@@ -122,7 +122,7 @@ module ActiveSupport
     def valid_message?(signed_message)
       return if signed_message.nil? || !signed_message.valid_encoding? || signed_message.blank?
 
-      data, digest = signed_message.split("--".freeze)
+      data, digest = signed_message.split("--")
       data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data))
     end
 
@@ -150,7 +150,7 @@ module ActiveSupport
     def verified(signed_message, purpose: nil, **)
       if valid_message?(signed_message)
         begin
-          data = signed_message.split("--".freeze)[0]
+          data = signed_message.split("--")[0]
           message = Messages::Metadata.verify(decode(data), purpose)
           @serializer.load(message) if message
         rescue ArgumentError => argument_error
diff --git a/activesupport/lib/active_support/number_helper.rb b/activesupport/lib/active_support/number_helper.rb
index 8fd6e932f1..c75ad52b0c 100644
--- a/activesupport/lib/active_support/number_helper.rb
+++ b/activesupport/lib/active_support/number_helper.rb
@@ -85,6 +85,9 @@ module ActiveSupport
     #   number given by <tt>:format</tt>).  Accepts the same fields
     #   than <tt>:format</tt>, except <tt>%n</tt> is here the
     #   absolute value of the number.
+    # * <tt>:strip_insignificant_zeros</tt> - If +true+ removes
+    #   insignificant zeros after the decimal separator (defaults to
+    #   +false+).
     #
     # ==== Examples
     #
@@ -100,6 +103,8 @@ module ActiveSupport
     #   # => "&pound;1234567890,50"
     #   number_to_currency(1234567890.50, unit: '&pound;', separator: ',', delimiter: '', format: '%n %u')
     #   # => "1234567890,50 &pound;"
+    #   number_to_currency(1234567890.50, strip_insignificant_zeros: true)
+    #   # => "$1,234,567,890.5"
     def number_to_currency(number, options = {})
       NumberToCurrencyConverter.convert(number, options)
     end
diff --git a/activesupport/lib/active_support/number_helper/number_to_currency_converter.rb b/activesupport/lib/active_support/number_helper/number_to_currency_converter.rb
index a25e22cbd3..aef5b62aed 100644
--- a/activesupport/lib/active_support/number_helper/number_to_currency_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_currency_converter.rb
@@ -15,7 +15,7 @@ module ActiveSupport
         end
 
         rounded_number = NumberToRoundedConverter.convert(number, options)
-        format.gsub("%n".freeze, rounded_number).gsub("%u".freeze, options[:unit])
+        format.gsub("%n", rounded_number).gsub("%u", options[:unit])
       end
 
       private
diff --git a/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb b/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb
index d5b5706705..05427fef53 100644
--- a/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb
@@ -14,7 +14,7 @@ module ActiveSupport
       private
 
         def parts
-          left, right = number.to_s.split(".".freeze)
+          left, right = number.to_s.split(".")
           left.gsub!(delimiter_pattern) do |digit_to_delimit|
             "#{digit_to_delimit}#{options[:delimiter]}"
           end
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 03eb6671ec..908f788ee3 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
@@ -25,7 +25,7 @@ module ActiveSupport
 
         rounded_number = NumberToRoundedConverter.convert(number, options)
         unit = determine_unit(units, exponent)
-        format.gsub("%n".freeze, rounded_number).gsub("%u".freeze, unit).strip
+        format.gsub("%n", rounded_number).gsub("%u", unit).strip
       end
 
       private
diff --git a/activesupport/lib/active_support/number_helper/number_to_human_size_converter.rb b/activesupport/lib/active_support/number_helper/number_to_human_size_converter.rb
index 842f2fc8df..0c72096b72 100644
--- a/activesupport/lib/active_support/number_helper/number_to_human_size_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_human_size_converter.rb
@@ -22,7 +22,7 @@ module ActiveSupport
           human_size = number / (base**exponent)
           number_to_format = NumberToRoundedConverter.convert(human_size, options)
         end
-        conversion_format.gsub("%n".freeze, number_to_format).gsub("%u".freeze, unit)
+        conversion_format.gsub("%n", number_to_format).gsub("%u", unit)
       end
 
       private
diff --git a/activesupport/lib/active_support/number_helper/number_to_percentage_converter.rb b/activesupport/lib/active_support/number_helper/number_to_percentage_converter.rb
index 4dcdad2e2c..6618ecffd5 100644
--- a/activesupport/lib/active_support/number_helper/number_to_percentage_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_percentage_converter.rb
@@ -7,7 +7,7 @@ module ActiveSupport
 
       def convert
         rounded_number = NumberToRoundedConverter.convert(number, options)
-        options[:format].gsub("%n".freeze, rounded_number)
+        options[:format].gsub("%n", rounded_number)
       end
     end
   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 eb528a0583..0ee5ef92dd 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
@@ -20,9 +20,9 @@ module ActiveSupport
           formatted_string =
             if BigDecimal === rounded_number && rounded_number.finite?
               s = rounded_number.to_s("F")
-              s << "0".freeze * precision
-              a, b = s.split(".".freeze, 2)
-              a << ".".freeze
+              s << "0" * precision
+              a, b = s.split(".", 2)
+              a << "."
               a << b[0, precision]
             else
               "%00.#{precision}f" % rounded_number
diff --git a/activesupport/lib/active_support/subscriber.rb b/activesupport/lib/active_support/subscriber.rb
index 5a4c3d74af..9562149f8d 100644
--- a/activesupport/lib/active_support/subscriber.rb
+++ b/activesupport/lib/active_support/subscriber.rb
@@ -92,7 +92,7 @@ module ActiveSupport
       event.finish!
       event.payload.merge!(payload)
 
-      method = name.split(".".freeze).first
+      method = name.split(".").first
       send(method, event)
     end
 
diff --git a/activesupport/lib/active_support/tagged_logging.rb b/activesupport/lib/active_support/tagged_logging.rb
index b069ac94d4..d8a86d997e 100644
--- a/activesupport/lib/active_support/tagged_logging.rb
+++ b/activesupport/lib/active_support/tagged_logging.rb
@@ -46,7 +46,7 @@ module ActiveSupport
 
       def current_tags
         # We use our object ID here to avoid conflicting with other instances
-        thread_key = @thread_key ||= "activesupport_tagged_logging_tags:#{object_id}".freeze
+        thread_key = @thread_key ||= "activesupport_tagged_logging_tags:#{object_id}"
         Thread.current[thread_key] ||= []
       end
 
@@ -61,8 +61,15 @@ module ActiveSupport
     end
 
     def self.new(logger)
-      # Ensure we set a default formatter so we aren't extending nil!
-      logger.formatter ||= ActiveSupport::Logger::SimpleFormatter.new
+      logger = logger.dup
+
+      if logger.formatter
+        logger.formatter = logger.formatter.dup
+      else
+        # Ensure we set a default formatter so we aren't extending nil!
+        logger.formatter = ActiveSupport::Logger::SimpleFormatter.new
+      end
+
       logger.formatter.extend Formatter
       logger.extend(self)
     end
diff --git a/activesupport/lib/active_support/test_case.rb b/activesupport/lib/active_support/test_case.rb
index f17743b6db..ef12c6b9b0 100644
--- a/activesupport/lib/active_support/test_case.rb
+++ b/activesupport/lib/active_support/test_case.rb
@@ -65,8 +65,8 @@ module ActiveSupport
       #
       #   parallelize(workers: 2, with: :threads)
       #
-      # The threaded parallelization uses Minitest's parallel executor directly.
-      # The processes parallelization uses a Ruby Drb server.
+      # The threaded parallelization uses minitest's parallel executor directly.
+      # The processes parallelization uses a Ruby DRb server.
       def parallelize(workers: 2, with: :processes)
         workers = ENV["PARALLEL_WORKERS"].to_i if ENV["PARALLEL_WORKERS"]
 
diff --git a/activesupport/lib/active_support/testing/method_call_assertions.rb b/activesupport/lib/active_support/testing/method_call_assertions.rb
index c6358002ea..fdc70e1cd3 100644
--- a/activesupport/lib/active_support/testing/method_call_assertions.rb
+++ b/activesupport/lib/active_support/testing/method_call_assertions.rb
@@ -35,6 +35,35 @@ module ActiveSupport
           assert_called(object, method_name, message, times: 0, &block)
         end
 
+        # TODO: No need to resort to #send once support for Ruby 2.4 is
+        # dropped.
+        def assert_called_on_instance_of(klass, method_name, message = nil, times: 1, returns: nil)
+          times_called = 0
+          klass.send(:define_method, "stubbed_#{method_name}") do |*|
+            times_called += 1
+
+            returns
+          end
+
+          klass.send(:alias_method, "original_#{method_name}", method_name)
+          klass.send(:alias_method, method_name, "stubbed_#{method_name}")
+
+          yield
+
+          error = "Expected #{method_name} to be called #{times} times, but was called #{times_called} times"
+          error = "#{message}.\n#{error}" if message
+
+          assert_equal times, times_called, error
+        ensure
+          klass.send(:alias_method, method_name, "original_#{method_name}")
+          klass.send(:undef_method, "original_#{method_name}")
+          klass.send(:undef_method, "stubbed_#{method_name}")
+        end
+
+        def assert_not_called_on_instance_of(klass, method_name, message = nil, &block)
+          assert_called_on_instance_of(klass, method_name, message, times: 0, &block)
+        end
+
         def stub_any_instance(klass, instance: klass.new)
           klass.stub(:new, instance) { yield instance }
         end
diff --git a/activesupport/lib/active_support/testing/parallelization.rb b/activesupport/lib/active_support/testing/parallelization.rb
index 1caac1feb3..beeb470659 100644
--- a/activesupport/lib/active_support/testing/parallelization.rb
+++ b/activesupport/lib/active_support/testing/parallelization.rb
@@ -65,22 +65,24 @@ module ActiveSupport
       def start
         @pool = @queue_size.times.map do |worker|
           fork do
-            DRb.stop_service
+            begin
+              DRb.stop_service
 
-            after_fork(worker)
+              after_fork(worker)
 
-            queue = DRbObject.new_with_uri(@url)
+              queue = DRbObject.new_with_uri(@url)
 
-            while job = queue.pop
-              klass    = job[0]
-              method   = job[1]
-              reporter = job[2]
-              result   = Minitest.run_one_method(klass, method)
+              while job = queue.pop
+                klass    = job[0]
+                method   = job[1]
+                reporter = job[2]
+                result   = Minitest.run_one_method(klass, method)
 
-              queue.record(reporter, result)
+                queue.record(reporter, result)
+              end
+            ensure
+              run_cleanup(worker)
             end
-
-            run_cleanup(worker)
           end
         end
       end
diff --git a/activesupport/lib/active_support/testing/time_helpers.rb b/activesupport/lib/active_support/testing/time_helpers.rb
index 801ea2909b..f160e66971 100644
--- a/activesupport/lib/active_support/testing/time_helpers.rb
+++ b/activesupport/lib/active_support/testing/time_helpers.rb
@@ -158,7 +158,7 @@ module ActiveSupport
       end
 
       # Returns the current time back to its original state, by removing the stubs added by
-      # +travel+ and +travel_to+.
+      # +travel+, +travel_to+, and +freeze_time+.
       #
       #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
       #   travel_to Time.zone.local(2004, 11, 24, 01, 04, 44)
@@ -168,6 +168,7 @@ module ActiveSupport
       def travel_back
         simple_stubs.unstub_all!
       end
+      alias_method :unfreeze_time, :travel_back
 
       # Calls +travel_to+ with +Time.now+.
       #
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index 7e71318404..3be5f6f7b5 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -43,8 +43,8 @@ module ActiveSupport
       "Time"
     end
 
-    PRECISIONS = Hash.new { |h, n| h[n] = "%FT%T.%#{n}N".freeze }
-    PRECISIONS[0] = "%FT%T".freeze
+    PRECISIONS = Hash.new { |h, n| h[n] = "%FT%T.%#{n}N" }
+    PRECISIONS[0] = "%FT%T"
 
     include Comparable, DateAndTime::Compatibility
     attr_reader :time_zone
@@ -147,7 +147,7 @@ module ActiveSupport
     #
     #   Time.zone.now.xmlschema  # => "2014-12-04T11:02:37-05:00"
     def xmlschema(fraction_digits = 0)
-      "#{time.strftime(PRECISIONS[fraction_digits.to_i])}#{formatted_offset(true, 'Z'.freeze)}"
+      "#{time.strftime(PRECISIONS[fraction_digits.to_i])}#{formatted_offset(true, 'Z')}"
     end
     alias_method :iso8601, :xmlschema
     alias_method :rfc3339, :xmlschema
@@ -286,8 +286,10 @@ module ActiveSupport
     alias_method :since, :+
     alias_method :in, :+
 
-    # Returns a new TimeWithZone object that represents the difference between
-    # the current object's time and the +other+ time.
+    # Subtracts an interval of time and returns a new TimeWithZone object unless
+    # the other value `acts_like?` time. Then it will return a Float of the difference
+    # between the two times that represents the difference between the current
+    # object's time and the +other+ time.
     #
     #   Time.zone = 'Eastern Time (US & Canada)' # => 'Eastern Time (US & Canada)'
     #   now = Time.zone.now # => Mon, 03 Nov 2014 00:26:28 EST -05:00
@@ -302,6 +304,12 @@ module ActiveSupport
     #
     #   now - 24.hours      # => Sun, 02 Nov 2014 01:26:28 EDT -04:00
     #   now - 1.day         # => Sun, 02 Nov 2014 00:26:28 EDT -04:00
+    #
+    # If both the TimeWithZone object and the other value act like Time, a Float
+    # will be returned.
+    #
+    #   Time.zone.now - 1.day.ago # => 86399.999967
+    #
     def -(other)
       if other.acts_like?(:time)
         to_time - other.to_time
diff --git a/activesupport/lib/active_support/xml_mini/jdom.rb b/activesupport/lib/active_support/xml_mini/jdom.rb
index 7f94a64016..32fe6ade28 100644
--- a/activesupport/lib/active_support/xml_mini/jdom.rb
+++ b/activesupport/lib/active_support/xml_mini/jdom.rb
@@ -18,7 +18,7 @@ module ActiveSupport
   module XmlMini_JDOM #:nodoc:
     extend self
 
-    CONTENT_KEY = "__content__".freeze
+    CONTENT_KEY = "__content__"
 
     NODE_TYPE_NAMES = %w{ATTRIBUTE_NODE CDATA_SECTION_NODE COMMENT_NODE DOCUMENT_FRAGMENT_NODE
     DOCUMENT_NODE DOCUMENT_TYPE_NODE ELEMENT_NODE ENTITY_NODE ENTITY_REFERENCE_NODE NOTATION_NODE
@@ -169,7 +169,7 @@ module ActiveSupport
       # element::
       #   XML element to be checked.
       def empty_content?(element)
-        text = "".dup
+        text = +""
         child_nodes = element.child_nodes
         (0...child_nodes.length).each do |i|
           item = child_nodes.item(i)
diff --git a/activesupport/lib/active_support/xml_mini/libxml.rb b/activesupport/lib/active_support/xml_mini/libxml.rb
index 0b000fea60..c2e999ef6c 100644
--- a/activesupport/lib/active_support/xml_mini/libxml.rb
+++ b/activesupport/lib/active_support/xml_mini/libxml.rb
@@ -34,7 +34,7 @@ module LibXML #:nodoc:
     end
 
     module Node #:nodoc:
-      CONTENT_ROOT = "__content__".freeze
+      CONTENT_ROOT = "__content__"
 
       # Convert XML document to hash.
       #
@@ -55,7 +55,7 @@ module LibXML #:nodoc:
           if c.element?
             c.to_hash(node_hash)
           elsif c.text? || c.cdata?
-            node_hash[CONTENT_ROOT] ||= "".dup
+            node_hash[CONTENT_ROOT] ||= +""
             node_hash[CONTENT_ROOT] << c.content
           end
         end
diff --git a/activesupport/lib/active_support/xml_mini/libxmlsax.rb b/activesupport/lib/active_support/xml_mini/libxmlsax.rb
index dcf16e6084..ac8acdfc3c 100644
--- a/activesupport/lib/active_support/xml_mini/libxmlsax.rb
+++ b/activesupport/lib/active_support/xml_mini/libxmlsax.rb
@@ -13,8 +13,8 @@ module ActiveSupport
     class HashBuilder
       include LibXML::XML::SaxParser::Callbacks
 
-      CONTENT_KEY   = "__content__".freeze
-      HASH_SIZE_KEY = "__hash_size__".freeze
+      CONTENT_KEY   = "__content__"
+      HASH_SIZE_KEY = "__hash_size__"
 
       attr_reader :hash
 
@@ -23,7 +23,7 @@ module ActiveSupport
       end
 
       def on_start_document
-        @hash = { CONTENT_KEY => "".dup }
+        @hash = { CONTENT_KEY => +"" }
         @hash_stack = [@hash]
       end
 
@@ -33,7 +33,7 @@ module ActiveSupport
       end
 
       def on_start_element(name, attrs = {})
-        new_hash = { CONTENT_KEY => "".dup }.merge!(attrs)
+        new_hash = { CONTENT_KEY => +"" }.merge!(attrs)
         new_hash[HASH_SIZE_KEY] = new_hash.size + 1
 
         case current_hash[name]
diff --git a/activesupport/lib/active_support/xml_mini/nokogiri.rb b/activesupport/lib/active_support/xml_mini/nokogiri.rb
index 5ee6fc8159..f76513f48b 100644
--- a/activesupport/lib/active_support/xml_mini/nokogiri.rb
+++ b/activesupport/lib/active_support/xml_mini/nokogiri.rb
@@ -38,7 +38,7 @@ module ActiveSupport
       end
 
       module Node #:nodoc:
-        CONTENT_ROOT = "__content__".freeze
+        CONTENT_ROOT = "__content__"
 
         # Convert XML document to hash.
         #
@@ -59,7 +59,7 @@ module ActiveSupport
             if c.element?
               c.to_hash(node_hash)
             elsif c.text? || c.cdata?
-              node_hash[CONTENT_ROOT] ||= "".dup
+              node_hash[CONTENT_ROOT] ||= +""
               node_hash[CONTENT_ROOT] << c.content
             end
           end
diff --git a/activesupport/lib/active_support/xml_mini/nokogirisax.rb b/activesupport/lib/active_support/xml_mini/nokogirisax.rb
index b01ed00a14..55cd72e093 100644
--- a/activesupport/lib/active_support/xml_mini/nokogirisax.rb
+++ b/activesupport/lib/active_support/xml_mini/nokogirisax.rb
@@ -16,8 +16,8 @@ module ActiveSupport
     # Class that will build the hash while the XML document
     # is being parsed using SAX events.
     class HashBuilder < Nokogiri::XML::SAX::Document
-      CONTENT_KEY   = "__content__".freeze
-      HASH_SIZE_KEY = "__hash_size__".freeze
+      CONTENT_KEY   = "__content__"
+      HASH_SIZE_KEY = "__hash_size__"
 
       attr_reader :hash
 
@@ -39,7 +39,7 @@ module ActiveSupport
       end
 
       def start_element(name, attrs = [])
-        new_hash = { CONTENT_KEY => "".dup }.merge!(Hash[attrs])
+        new_hash = { CONTENT_KEY => +"" }.merge!(Hash[attrs])
         new_hash[HASH_SIZE_KEY] = new_hash.size + 1
 
         case current_hash[name]
diff --git a/activesupport/lib/active_support/xml_mini/rexml.rb b/activesupport/lib/active_support/xml_mini/rexml.rb
index 32458d5b0d..8d6e3af066 100644
--- a/activesupport/lib/active_support/xml_mini/rexml.rb
+++ b/activesupport/lib/active_support/xml_mini/rexml.rb
@@ -8,7 +8,7 @@ module ActiveSupport
   module XmlMini_REXML #:nodoc:
     extend self
 
-    CONTENT_KEY = "__content__".freeze
+    CONTENT_KEY = "__content__"
 
     # Parse an XML Document string or IO into a simple hash.
     #
@@ -76,7 +76,7 @@ module ActiveSupport
           hash
         else
           # must use value to prevent double-escaping
-          texts = "".dup
+          texts = +""
           element.texts.each { |t| texts << t.value }
           merge!(hash, CONTENT_KEY, texts)
         end