Passing a Class to ActiveSupport::Digest.hash_digest_class is depre…

…cated in favour of String.

    Before:

        ActiveSupport::Digest.hash_digest_class = OpenSSL::Digest::SHA256

    After:

        ActiveSupport::Digest.hash_digest_class = "SHA256"

Related discussions:
ruby/openssl#362
ruby/openssl#304
#39410
Sibling PR: #39504

activesupport/CHANGELOG.md

@@ -1,3 +1,15 @@
+*   Passing a Class to `ActiveSupport::Digest.hash_digest_class` is deprecated in favour of String.
+
+    Before:
+
+        ActiveSupport::Digest.hash_digest_class = OpenSSL::Digest::SHA256
+              
+    After:
+
+        ActiveSupport::Digest.hash_digest_class = "SHA256"
+
+    *Vipul A M*
+
 *   `require_dependency` has been documented to be _obsolete_ in `:zeitwerk`
     mode. The method is not deprecated as such (yet), but applications are
     encouraged to not use it.

activesupport/lib/active_support/digest.rb

@@ -1,19 +1,29 @@
 # frozen_string_literal: true
 
+require "openssl"
+
 module ActiveSupport
   class Digest #:nodoc:
     class <<self
       def hash_digest_class
-        @hash_digest_class ||= ::Digest::MD5
+        @hash_digest_class ||= "MD5"
       end
 
       def hash_digest_class=(klass)
-        raise ArgumentError, "#{klass} is expected to implement hexdigest class method" unless klass.respond_to?(:hexdigest)
+        unless klass.is_a?(String)
+          klass = klass.to_s.split("::").last.to_s
+          ActiveSupport::Deprecation.warn(<<~EOM)
+            Passing a Digest Class to `hash_digest_class=` is deprecated and will be removed in future
+            versions of Rails. Please pass a string instead (SHA1, SHA256, MD5, etc).
+          EOM
+        end
+
+        raise ArgumentError, "#{klass} is unsupported by OpenSSL::Digest" unless OpenSSL::Digest.const_defined?(klass)
         @hash_digest_class = klass
       end
 
       def hexdigest(arg)
-        hash_digest_class.hexdigest(arg)[0...32]
+        OpenSSL::Digest.hexdigest(hash_digest_class, arg)[0...32]
       end
     end
   end

activesupport/lib/active_support/railtie.rb

@@ -85,7 +85,7 @@ class Railtie < Rails::Railtie # :nodoc:
     initializer "active_support.set_hash_digest_class" do |app|
       config.after_initialize do
         if app.config.active_support.use_sha1_digests
-          ActiveSupport::Digest.hash_digest_class = ::Digest::SHA1
+          ActiveSupport::Digest.hash_digest_class = "SHA1"
         end
       end
     end

activesupport/test/digest_test.rb

@@ -6,22 +6,24 @@
 class DigestTest < ActiveSupport::TestCase
   class InvalidDigest; end
   def test_with_default_hash_digest_class
-    assert_equal ::Digest::MD5.hexdigest("hello friend"), ActiveSupport::Digest.hexdigest("hello friend")
+    assert_equal OpenSSL::Digest.hexdigest("MD5", "hello friend"), ActiveSupport::Digest.hexdigest("hello friend")
   end
 
   def test_with_custom_hash_digest_class
     original_hash_digest_class = ActiveSupport::Digest.hash_digest_class
-
-    ActiveSupport::Digest.hash_digest_class = ::Digest::SHA1
+    ActiveSupport::Digest.hash_digest_class = "SHA1"
     digest = ActiveSupport::Digest.hexdigest("hello friend")
 
     assert_equal 32, digest.length
-    assert_equal ::Digest::SHA1.hexdigest("hello friend")[0...32], digest
+    assert_equal OpenSSL::Digest.hexdigest("SHA1", "hello friend")[0...32], digest
   ensure
     ActiveSupport::Digest.hash_digest_class = original_hash_digest_class
   end
 
   def test_should_raise_argument_error_if_custom_digest_is_missing_hexdigest_method
-    assert_raises(ArgumentError) { ActiveSupport::Digest.hash_digest_class = InvalidDigest }
+    assert_deprecated(/Passing a Digest Class to `hash_digest_class=` is deprecated and will be removed in future/) do
+      assert_raises(ArgumentError) { ActiveSupport::Digest.hash_digest_class = InvalidDigest }
+      assert_raises(ArgumentError) { ActiveSupport::Digest.hash_digest_class = "InvalidDigest" }
+    end
   end
 end

railties/test/application/configuration_test.rb

@@ -2172,18 +2172,18 @@ class D < C
       assert_equal true, ActiveSupport::MessageEncryptor.use_authenticated_message_encryption
     end
 
-    test "ActiveSupport::Digest.hash_digest_class is Digest::SHA1 by default for new apps" do
+    test "ActiveSupport::Digest.hash_digest_class is SHA1 by default for new apps" do
       app "development"
 
-      assert_equal Digest::SHA1, ActiveSupport::Digest.hash_digest_class
+      assert_equal "SHA1", ActiveSupport::Digest.hash_digest_class
     end
 
-    test "ActiveSupport::Digest.hash_digest_class is Digest::MD5 by default for upgraded apps" do
+    test "ActiveSupport::Digest.hash_digest_class is MD5 by default for upgraded apps" do
       remove_from_config '.*config\.load_defaults.*\n'
 
       app "development"
 
-      assert_equal Digest::MD5, ActiveSupport::Digest.hash_digest_class
+      assert_equal "MD5", ActiveSupport::Digest.hash_digest_class
     end
 
     test "ActiveSupport::Digest.hash_digest_class can be configured via config.active_support.use_sha1_digests" do
@@ -2195,7 +2195,7 @@ class D < C
 
       app "development"
 
-      assert_equal Digest::SHA1, ActiveSupport::Digest.hash_digest_class
+      assert_equal "SHA1", ActiveSupport::Digest.hash_digest_class
     end
 
     test "custom serializers should be able to set via config.active_job.custom_serializers in an initializer" do