Don't require BigDecimal serialization extension

Rails currently provides an extension to BigDecimal that redefines how
it is serialized to YAML. However, as noted in #12467, this does not
work as expected. When ActiveSupport is required, BigDecimal YAML
serialization does not maintain the object type. It instead ends up
serializing the number represented by the BigDecimal itself which, when
loaded by YAML later, becomes a Float:

```ruby
require 'yaml'
require 'bigdecimal'

yaml = BigDecimal('13.37').to_yaml
YAML.load(yaml).class

require 'active_support/all'

yaml = BigDecimal('13.37').to_yaml
YAML.load(yaml).class
```

@tenderlove posits that we should deprecate the custom BigDecimal
serialization and let Ruby handle it. For the time being, users who
require this serialization for backwards compatibility can manually
`require 'active_support/core_ext/big_decimal/yaml_conversions'`.

This will close #12467 and deprecate the custom BigDecimal#to_yaml.

Signed-off-by: David Celis <me@davidcel.is>

5 files changed, 33 insertions, 16 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index b44df1b8a9..f15bd1b8d0 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   Deprecate custom `BigDecimal` serialization
+
+    Deprecate the custom `BigDecimal` serialization that is included when requiring
+    `active_support/all` as a fix for #12467. Let Ruby handle YAML serialization
+    for `BigDecimal` instead.
+
+    *David Celis*
+
 *   Maintain the current timezone when calling `wrap_with_time_zone`
 
     Extend the solution from the fix for #12163 to the general case where `Time`
diff --git a/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb b/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb
index 39b8cea807..54b49e6d04 100644
--- a/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb
@@ -1,15 +1,7 @@
 require 'bigdecimal'
 require 'bigdecimal/util'
-require 'yaml'
 
 class BigDecimal
-  YAML_MAPPING = { 'Infinity' => '.Inf', '-Infinity' => '-.Inf', 'NaN' => '.NaN' }
-
-  def encode_with(coder)
-    string = to_s
-    coder.represent_scalar(nil, YAML_MAPPING[string] || string)
-  end
-
   # Backport this method if it doesn't exist
   unless method_defined?(:to_d)
     def to_d
diff --git a/activesupport/lib/active_support/core_ext/big_decimal/yaml_conversions.rb b/activesupport/lib/active_support/core_ext/big_decimal/yaml_conversions.rb
new file mode 100644
index 0000000000..aa2ed4d6fb
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/big_decimal/yaml_conversions.rb
@@ -0,0 +1,13 @@
+ActiveSupport::Deprecation.warn 'core_ext/big_decimal/yaml_conversions is deprecated and will be removed in the future.'
+
+require 'bigdecimal'
+require 'yaml'
+
+class BigDecimal
+  YAML_MAPPING = { 'Infinity' => '.Inf', '-Infinity' => '-.Inf', 'NaN' => '.NaN' }
+
+  def encode_with(coder)
+    string = to_s
+    coder.represent_scalar(nil, YAML_MAPPING[string] || string)
+  end
+end
diff --git a/activesupport/test/core_ext/big_decimal/yaml_conversions_test.rb b/activesupport/test/core_ext/big_decimal/yaml_conversions_test.rb
new file mode 100644
index 0000000000..49020e0567
--- /dev/null
+++ b/activesupport/test/core_ext/big_decimal/yaml_conversions_test.rb
@@ -0,0 +1,11 @@
+require 'abstract_unit'
+require 'active_support/core_ext/big_decimal/yaml_conversions'
+
+class BigDecimalYamlConversionsTest < ActiveSupport::TestCase
+  def test_to_yaml
+    assert_match("--- 100000.30020320320000000000000000000000000000001\n", BigDecimal.new('100000.30020320320000000000000000000000000000001').to_yaml)
+    assert_match("--- .Inf\n",  BigDecimal.new('Infinity').to_yaml)
+    assert_match("--- .NaN\n",  BigDecimal.new('NaN').to_yaml)
+    assert_match("--- -.Inf\n", BigDecimal.new('-Infinity').to_yaml)
+  end
+end
diff --git a/activesupport/test/core_ext/bigdecimal_test.rb b/activesupport/test/core_ext/bigdecimal_test.rb
index b386e55d6c..61bf3f81e6 100644
--- a/activesupport/test/core_ext/bigdecimal_test.rb
+++ b/activesupport/test/core_ext/bigdecimal_test.rb
@@ -2,18 +2,11 @@ require 'abstract_unit'
 require 'active_support/core_ext/big_decimal'
 
 class BigDecimalTest < ActiveSupport::TestCase
-  def test_to_yaml
-    assert_match("--- 100000.30020320320000000000000000000000000000001\n", BigDecimal.new('100000.30020320320000000000000000000000000000001').to_yaml)
-    assert_match("--- .Inf\n",  BigDecimal.new('Infinity').to_yaml)
-    assert_match("--- .NaN\n",  BigDecimal.new('NaN').to_yaml)
-    assert_match("--- -.Inf\n", BigDecimal.new('-Infinity').to_yaml)
-  end
-
   def test_to_d
     bd = BigDecimal.new '10'
     assert_equal bd, bd.to_d
   end
-  
+
   def test_to_s
     bd = BigDecimal.new '0.01'
     assert_equal '0.01', bd.to_s