`HashWithIndifferentAccess.new` respects the default value or proc on objects that respond to `#to_hash`.

Builds on the work of #12550 where `.new` will convert the object (that respond to `#to_hash`) to a hash and
add that hash's keys and values to itself.

This change will also make `.new` respect the default value or proc of objects that respond to `#to_hash`.
In other words, this `.new` behaves exactly like `.new_from_hash_copying_default`.

`.new_from_hash_copying_default` now simply invokes `.new` and any references to `.new_from_hash_copying_default`
are replaced with `.new`.

Added tests confirm behavior.

4 files changed, 32 insertions, 8 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 61e9927a07..3e68ca84d8 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   `HashWithIndifferentAccess.new` respects the default value or proc on objects
+    that respond to `#to_hash`. `.new_from_hash_copying_default` simply invokes `.new`.
+    All calls to `.new_from_hash_copying_default` are replaced with `.new`.
+
+    *Gordon Chan*
+
 *   `Object#with_options` executes block in merging option context when
     explicit receiver in not passed.
 
diff --git a/activesupport/lib/active_support/core_ext/hash/indifferent_access.rb b/activesupport/lib/active_support/core_ext/hash/indifferent_access.rb
index 28cb3e2a3b..6df7b4121b 100644
--- a/activesupport/lib/active_support/core_ext/hash/indifferent_access.rb
+++ b/activesupport/lib/active_support/core_ext/hash/indifferent_access.rb
@@ -6,7 +6,7 @@ class Hash
   #
   #   { a: 1 }.with_indifferent_access['a'] # => 1
   def with_indifferent_access
-    ActiveSupport::HashWithIndifferentAccess.new_from_hash_copying_default(self)
+    ActiveSupport::HashWithIndifferentAccess.new(self)
   end
 
   # Called when object is nested under an object that receives
diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index 30e27267a0..a400e71aa8 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -58,6 +58,10 @@ module ActiveSupport
       if constructor.respond_to?(:to_hash)
         super()
         update(constructor)
+
+        hash = constructor.to_hash
+        self.default = hash.default if hash.default
+        self.default_proc = hash.default_proc if hash.default_proc
       else
         super(constructor)
       end
@@ -72,11 +76,7 @@ module ActiveSupport
     end
 
     def self.new_from_hash_copying_default(hash)
-      hash = hash.to_hash
-      new(hash).tap do |new_hash|
-        new_hash.default = hash.default
-        new_hash.default_proc = hash.default_proc if hash.default_proc
-      end
+      new(hash)
     end
 
     def self.[](*args)
@@ -205,7 +205,7 @@ module ActiveSupport
     #   hash['a'] = nil
     #   hash.reverse_merge(a: 0, b: 1) # => {"a"=>nil, "b"=>1}
     def reverse_merge(other_hash)
-      super(self.class.new_from_hash_copying_default(other_hash))
+      super(self.class.new(other_hash))
     end
 
     # Same semantics as +reverse_merge+ but modifies the receiver in-place.
@@ -218,7 +218,7 @@ module ActiveSupport
     #   h = { "a" => 100, "b" => 200 }
     #   h.replace({ "c" => 300, "d" => 400 }) # => {"c"=>300, "d"=>400}
     def replace(other_hash)
-      super(self.class.new_from_hash_copying_default(other_hash))
+      super(self.class.new(other_hash))
     end
 
     # Removes the specified key from the hash.
diff --git a/activesupport/test/core_ext/hash_ext_test.rb b/activesupport/test/core_ext/hash_ext_test.rb
index dbbb2d77da..b71206d2e3 100644
--- a/activesupport/test/core_ext/hash_ext_test.rb
+++ b/activesupport/test/core_ext/hash_ext_test.rb
@@ -996,6 +996,24 @@ class HashExtTest < ActiveSupport::TestCase
     assert hash.key?('a')
     assert_equal 1, hash[:a]
   end
+
+  def test_new_with_to_hash_conversion_copies_default
+    normal_hash = Hash.new(3)
+    normal_hash[:a] = 1
+
+    hash = HashWithIndifferentAccess.new(HashByConversion.new(normal_hash))
+    assert_equal 1, hash[:a]
+    assert_equal 3, hash[:b]
+  end
+
+  def test_new_with_to_hash_conversion_copies_default_proc
+    normal_hash = Hash.new { 1 + 2 }
+    normal_hash[:a] = 1
+
+    hash = HashWithIndifferentAccess.new(HashByConversion.new(normal_hash))
+    assert_equal 1, hash[:a]
+    assert_equal 3, hash[:b]
+  end
 end
 
 class IWriteMyOwnXML