active_support test began to fail beginning with json 2.7.3

[mtasaka]

This test:
https://github.com/rails/rails/blob/d0dcb8fa6073a0c4d42600c15e82e3bb386b27d3/activesupport/test/json/encoding_test.rb#L55

began to fail. git bisect shows the above began to fail with:
e125072

Extracted self-contained test case:

#!/usr/bin/ruby

require "minitest"
require "json"
require 'forwardable'
require 'minitest/autorun'

module ActiveSupport
  class TestCase < ::Minitest::Test
    Assertion = Minitest::Assertion

    class << self
    end

  end
end

class String
  def as_json(options = nil) # :nodoc:
    self
  end
end

class Hash
  def as_json(options = nil) # :nodoc:
    # create a subset of the hash by applying :only or :except
    subset = if options
      if attrs = options[:only]
        slice(*Array(attrs))
      elsif attrs = options[:except]
        except(*Array(attrs))
      else
        self
      end
    else
      self
    end

    result = {}
    subset.each do |k, v|
      result[k.to_s] = options ? v.as_json(options.dup) : v.as_json
    end
    result
  end
end

module ActiveSupport
  class << self
    extend Forwardable
    def_delegators :'ActiveSupport::JSON::Encoding',
      :use_standard_json_time_format, :use_standard_json_time_format=,
      :time_precision, :time_precision=,
      :escape_html_entities_in_json, :escape_html_entities_in_json=,
      :json_encoder, :json_encoder=
  end

  module JSON
    # Dumps objects in JSON (JavaScript Object Notation).
    # See http://www.json.org for more info.
    #
    #   ActiveSupport::JSON.encode({ team: 'rails', players: '36' })
    #   # => "{\"team\":\"rails\",\"players\":\"36\"}"
    def self.encode(value, options = nil)
      Encoding.json_encoder.new(options).encode(value)
    end

    module Encoding # :nodoc:
      class JSONGemEncoder # :nodoc:
        attr_reader :options

        def initialize(options = nil)
          @options = options || {}
        end

        # Encode the given object into a JSON string
        def encode(value)
          stringify jsonify value.as_json(options.dup)
        end

        private
          # Rails does more escaping than the JSON gem natively does (we
          # escape \u2028 and \u2029 and optionally >, <, & to work around
          # certain browser problems).
          ESCAPED_CHARS = {
            "\u2028" => '\u2028',
            "\u2029" => '\u2029',
            ">"      => '\u003e',
            "<"      => '\u003c',
            "&"      => '\u0026',
            }

          ESCAPE_REGEX_WITH_HTML_ENTITIES = /[\u2028\u2029><&]/u
          ESCAPE_REGEX_WITHOUT_HTML_ENTITIES = /[\u2028\u2029]/u

          # This class wraps all the strings we see and does the extra escaping
          class EscapedString < String # :nodoc:
            def to_json(*)
              if Encoding.escape_html_entities_in_json
                s = super
                s.gsub! ESCAPE_REGEX_WITH_HTML_ENTITIES, ESCAPED_CHARS
                s
              else
                s = super
                s.gsub! ESCAPE_REGEX_WITHOUT_HTML_ENTITIES, ESCAPED_CHARS
                s
              end
            end

            def to_s
              self
            end
          end

          # Mark these as private so we don't leak encoding-specific constructs
          private_constant :ESCAPED_CHARS, :ESCAPE_REGEX_WITH_HTML_ENTITIES,
            :ESCAPE_REGEX_WITHOUT_HTML_ENTITIES, :EscapedString

          # Convert an object into a "JSON-ready" representation composed of
          # primitives like Hash, Array, String, Numeric,
          # and +true+/+false+/+nil+.
          # Recursively calls #as_json to the object to recursively build a
          # fully JSON-ready object.
          #
          # This allows developers to implement #as_json without having to
          # worry about what base types of objects they are allowed to return
          # or having to remember to call #as_json recursively.
          #
          # Note: the +options+ hash passed to +object.to_json+ is only passed
          # to +object.as_json+, not any of this method's recursive +#as_json+
          # calls.
          def jsonify(value)
            case value
            when String
              EscapedString.new(value)
            when Numeric, NilClass, TrueClass, FalseClass
              value.as_json
            when Hash
              result = {}
              value.each do |k, v|
                result[jsonify(k)] = jsonify(v)
              end
              result
            when Array
              value.map { |v| jsonify(v) }
            else
              jsonify value.as_json
            end
          end

          # Encode a "jsonified" Ruby data structure using the JSON gem
          def stringify(jsonified)
            ::JSON.generate(jsonified, quirks_mode: true, max_nesting: false)
           end
      end

      class << self
        # If true, use ISO 8601 format for dates and times. Otherwise, fall back
        # to the Active Support legacy format.
        attr_accessor :use_standard_json_time_format

        # If true, encode >, <, & as escaped unicode sequences (e.g. > as \u003e)
        # as a safety measure.
        attr_accessor :escape_html_entities_in_json

        # Sets the precision of encoded time values.
        # Defaults to 3 (equivalent to millisecond precision)
        attr_accessor :time_precision

        # Sets the encoder used by Rails to encode Ruby objects into JSON strings
        # in +Object#to_json+ and +ActiveSupport::JSON.encode+.
        attr_accessor :json_encoder
      end

      self.use_standard_json_time_format = true
      self.escape_html_entities_in_json  = true
      self.json_encoder = JSONGemEncoder
      self.time_precision = 3
    end
  end
end

class TestJSONEncoding < ActiveSupport::TestCase
  def test_hash_keys_encoding
    ActiveSupport.escape_html_entities_in_json = true
    assert_equal "{\"\\u003c\\u003e\":\"\\u003c\\u003e\"}", ActiveSupport::JSON.encode("<>" => "<>")
  ensure
    ActiveSupport.escape_html_entities_in_json = false
  end
end

Failure message:

Run options: --seed 44396

# Running:

F

Finished in 0.005829s, 171.5561 runs/s, 171.5561 assertions/s.

  1) Failure:
TestJSONEncoding#test_hash_keys_encoding [./json_test.rb:185]:
--- expected
+++ actual
@@ -1,3 +1,3 @@
 # encoding: UTF-8
 #    valid: true
-"{\"\\u003c\\u003e\":\"\\u003c\\u003e\"}"
+"{\"<>\":\"\\u003c\\u003e\"}"


1 runs, 1 assertions, 1 failures, 0 errors, 0 skips

[mtasaka]

Using:

$ ruby -v
ruby 3.3.5 (2024-09-03 revision ef084cc8f4) [x86_64-linux]