Deprecate decimal columns being automatically treated as integers

With ActiveRecord::Properties, we now have a reasonable path for users
to continue to keep this behavior if they want it. This is an edge case
that has added a lot of complexity to the code base.

3 files changed, 16 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index ca5db4095e..6ecd4efdc8 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -396,6 +396,7 @@ module ActiveRecord
           precision = extract_precision(sql_type)
 
           if scale == 0
+            # FIXME: Remove this class as well
             Type::DecimalWithoutScale.new(precision: precision)
           else
             Type::Decimal.new(precision: precision, scale: scale)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 1f327d1f2f..027169ae3c 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -478,6 +478,8 @@ module ActiveRecord
             # places after decimal  = fmod - 4 & 0xffff
             # places before decimal = (fmod - 4) >> 16 & 0xffff
             if fmod && (fmod - 4 & 0xffff).zero?
+              # FIXME: Remove this class, and the second argument to
+              # lookups on PG
               Type::DecimalWithoutScale.new(precision: precision)
             else
               OID::Decimal.new(precision: precision, scale: scale)
diff --git a/activerecord/lib/active_record/properties.rb b/activerecord/lib/active_record/properties.rb
index a5d724de0e..39c39ad9ff 100644
--- a/activerecord/lib/active_record/properties.rb
+++ b/activerecord/lib/active_record/properties.rb
@@ -64,7 +64,19 @@ module ActiveRecord
 
       # Returns an array of column objects for the table associated with this class.
       def columns
-        @columns ||= add_user_provided_columns(connection.schema_cache.columns(table_name))
+        @columns ||= add_user_provided_columns(connection.schema_cache.columns(table_name)).each do |column|
+          if Type::DecimalWithoutScale === column.cast_type
+            ActiveSupport::Deprecation.warn <<-MESSAGE.strip_heredoc
+              Decimal columns with 0 scale being automatically treated as integers
+              is deprecated, and will be removed in a future version of Rails. If
+              you'd like to keep this behavior, add
+
+                property :#{column.name}, Type::Integer.new
+
+              to your #{name} model.
+            MESSAGE
+          end
+        end
       end
 
       # Returns a hash of column objects for the table associated with this class.