Deprecate the top-level `HashWithIndifferentAccess` contant

This constant was kept for the sake of backward compatibility; it
is still available under `ActiveSupport::HashWithIndifferentAccess`.

Furthermore, since Ruby 2.5 (https://bugs.ruby-lang.org/issues/11547)
won't support top level constant lookup, people would have to update
their code anyway.

3 files changed, 46 insertions, 1 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 2fb7f29d73..788ea88752 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Deprecated the top level `HashWithIndifferentAccess` constant.
+
+    Only `ActiveSupport::HashWithIndifferentAccess` should be used now.
+
+    *Robin Dupret* (#27925)
+
 *   Deprecate `.halt_callback_chains_on_return_false`.
 
     *Rafael Mendonça França*
diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index 79e7feaf47..8638667082 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -316,4 +316,20 @@ module ActiveSupport
   end
 end
 
-HashWithIndifferentAccess = ActiveSupport::HashWithIndifferentAccess
+class HashWithIndifferentAccess < ActiveSupport::HashWithIndifferentAccess
+  def initialize(*)
+    ActiveSupport::Deprecation.warn "HashWithIndifferentAccess is deprecated!" \
+                                    "Use ActiveSupport::HashWithIndifferentAccess instead."
+    super
+  end
+
+  def self.inherited(*)
+    ActiveSupport::Deprecation.warn "HashWithIndifferentAccess is deprecated!" \
+                                    "Use ActiveSupport::HashWithIndifferentAccess instead."
+    super
+  end
+
+  def encode_with(coder)
+    coder.represent_object(nil, ActiveSupport::HashWithIndifferentAccess.new(self))
+  end
+end
diff --git a/activesupport/test/core_ext/hash_ext_test.rb b/activesupport/test/core_ext/hash_ext_test.rb
index 05813ad388..042bb60a22 100644
--- a/activesupport/test/core_ext/hash_ext_test.rb
+++ b/activesupport/test/core_ext/hash_ext_test.rb
@@ -8,6 +8,8 @@ require "active_support/core_ext/object/deep_dup"
 require "active_support/inflections"
 
 class HashExtTest < ActiveSupport::TestCase
+  HashWithIndifferentAccess = ActiveSupport::HashWithIndifferentAccess
+
   class IndifferentHash < ActiveSupport::HashWithIndifferentAccess
   end
 
@@ -1078,6 +1080,25 @@ class HashExtTest < ActiveSupport::TestCase
     assert_equal 1, hash[:a]
     assert_equal 3, hash[:b]
   end
+
+  def test_top_level_hash_with_indifferent_access_is_deprecated
+    assert_deprecated do
+      ::HashWithIndifferentAccess.new
+    end
+  end
+
+  def test_top_level_hash_with_indifferent_access_can_be_extended
+    assert_deprecated do
+      Class.new(::HashWithIndifferentAccess)
+    end
+  end
+
+  def test_yaml_encoding_outputs_an_activesupport_namespaced_constant
+    ActiveSupport::Deprecation.silence do
+      instance = ::HashWithIndifferentAccess.new
+      assert_includes instance.to_yaml, "ActiveSupport::HashWithIndifferentAccess"
+    end
+  end
 end
 
 class IWriteMyOwnXML
@@ -1123,6 +1144,8 @@ class HashExtToParamTests < ActiveSupport::TestCase
 end
 
 class HashToXmlTest < ActiveSupport::TestCase
+  HashWithIndifferentAccess = ActiveSupport::HashWithIndifferentAccess
+
   def setup
     @xml_options = { root: :person, skip_instruct: true, indent: 0 }
   end