Maybe encoding bug?

bug.rb

# frozen_string_literal: true

class Context < BasicObject
  def method_missing(name, *) = :identifier
  def self.const_missing(name) = :constant
end

$context = Context.new

def evaluate(encoding, codepoint)
  character = codepoint.chr(encoding)

  if character.match?(/[[:lower:]]/)
    type = $context.instance_eval("# encoding: #{encoding.name}\n#{character}")
    puts "#{encoding.name} 0x#{codepoint.to_s(16)}" if type != :identifier
  elsif character.match?(/[[:upper:]]/)
    type = $context.instance_eval("# encoding: #{encoding.name}\n#{character}")
    puts "#{encoding.name} 0x#{codepoint.to_s(16)}" if type != :constant
  end
end

encodings_7bits = [
  Encoding::US_ASCII
]

encodings_7bits.each do |encoding|
  (0..0x7F).each do |codepoint|
    evaluate(encoding, codepoint)
  end
end

encodings_1byte = [
  Encoding::ASCII_8BIT,
  Encoding::ISO8859_1,
  Encoding::ISO8859_2,
  Encoding::ISO8859_3,
  Encoding::ISO8859_4,
  Encoding::ISO8859_5,
  Encoding::ISO8859_6,
  Encoding::ISO8859_7,
  Encoding::ISO8859_8,
  Encoding::ISO8859_9,
  Encoding::ISO8859_10,
  Encoding::ISO8859_11,
  Encoding::ISO8859_13,
  Encoding::ISO8859_14,
  Encoding::ISO8859_15,
  Encoding::ISO8859_16,
  Encoding::CP878,
  Encoding::KOI8_U,
  Encoding::WINDOWS_1250,
  Encoding::WINDOWS_1251,
  Encoding::WINDOWS_1252,
  Encoding::WINDOWS_1253,
  Encoding::WINDOWS_1254,
  Encoding::WINDOWS_1257,
  Encoding::CP437,
  Encoding::CP720,
  Encoding::CP737,
  Encoding::CP775,
  Encoding::IBM850,
  Encoding::IBM852,
  Encoding::CP852,
  Encoding::IBM855,
  Encoding::CP855,
  Encoding::CP857,
  Encoding::CP860,
  Encoding::CP861,
  Encoding::CP862,
  Encoding::CP863,
  Encoding::CP864,
  Encoding::CP865,
  Encoding::CP866,
  Encoding::CP869,
  Encoding::CP1258,
  Encoding::GB1988,
  Encoding::MACCENTEURO,
  Encoding::MACCROATIAN,
  Encoding::MACCYRILLIC,
  Encoding::MACGREEK,
  Encoding::MACICELAND,
  Encoding::MACROMAN,
  Encoding::MACROMANIA,
  Encoding::MACTHAI,
  Encoding::MACTURKISH,
  Encoding::MACUKRAINE,
  Encoding::Windows_1256,
  Encoding::WINDOWS_1255,
  Encoding::TIS_620,
  Encoding::Windows_874
]

encodings_1byte.each do |encoding|
  (0..0xFF).each do |codepoint|
    evaluate(encoding, codepoint)
  end
end

encodings_2byte = [
  Encoding::BIG5,
  Encoding::BIG5_HKSCS_2008,
  Encoding::BIG5_UAO,
  Encoding::EUCKR,
  Encoding::EUCTW,
  Encoding::SHIFT_JIS,
  Encoding::SJIS_DOCOMO,
  Encoding::SJIS_KDDI,
  Encoding::SJIS_SOFTBANK,
  Encoding::WINDOWS_31J,
  Encoding::CP949,
  Encoding::GB18030,
  Encoding::CP936,
  Encoding::CP950,
  Encoding::CP951,
  Encoding::EUCCN,
  Encoding::GB12345,
  Encoding::MACJAPANESE
]

encodings_2byte.each do |encoding|
  (0..0xFFFF).each do |codepoint|
    evaluate(encoding, codepoint)
  rescue RangeError
  end
end

encodings_3byte = [
  Encoding::EUCJP,
  Encoding::EUC_JP_MS,
  Encoding::EUC_JISX0213,
  Encoding::CP51932
]

encodings_3byte.each do |encoding|
  (0..0xFFFFFF).each do |codepoint|
    evaluate(encoding, codepoint)
  rescue RangeError
  end
end

encodings_unicode = [
  Encoding::UTF_8,
  Encoding::UTF8_MAC,
  Encoding::UTF8_DoCoMo,
  Encoding::UTF8_KDDI,
  Encoding::UTF8_SoftBank,
  Encoding::CP65001,
  Encoding::CESU_8
]

encodings_unicode.each do |encoding|
  (0...0xD800).each do |codepoint|
    evaluate(encoding, codepoint)
  end

  (0xE000..0x10FFFF).each do |codepoint|
    evaluate(encoding, codepoint)
  end
end

encodings_4byte = [
  Encoding::EMACS_MULE,
  Encoding::STATELESS_ISO_2022_JP,
  Encoding::STATELESS_ISO_2022_JP_KDDI,
]

encodings_4byte.each do |encoding|
  (0..0xFFFFFFFF).each do |codepoint|
    evaluate(encoding, codepoint)
  rescue RangeError
  end
end