PostgreSQL: Allow BC dates like datetime consistently

BC dates are supported by both date and datetime types.

https://www.postgresql.org/docs/current/static/datatype-datetime.html

Since #1097, new datetime allows year zero as 1 BC, but new date does
not. It should be allowed even in new date consistently.

activemodel/lib/active_model/type/date.rb

@@ -42,7 +42,7 @@ module ActiveModel
         end
 
         def new_date(year, mon, mday)
-          if year && year != 0
+          unless year.nil? || (year == 0 && mon == 0 && mday == 0)
             ::Date.new(year, mon, mday) rescue nil
           end
         end

activerecord/lib/active_record/connection_adapters/postgresql/oid/date.rb

@@ -9,6 +9,9 @@ module ActiveRecord
             case value
             when "infinity" then ::Float::INFINITY
             when "-infinity" then -::Float::INFINITY
+            when / BC$/
+              astronomical_year = format("%04d", -value[/^\d+/].to_i + 1)
+              super(value.sub(/ BC$/, "").sub(/^\d+/, astronomical_year))
             else
               super
             end

activerecord/test/cases/adapters/postgresql/date_test.rb

@@ -21,4 +21,22 @@ class PostgresqlDateTest < ActiveRecord::PostgreSQLTestCase
     topic = Topic.create!(last_read: -1.0 / 0.0)
     assert_equal(-1.0 / 0.0, topic.last_read)
   end
+
+  def test_bc_date
+    date = Date.new(0) - 1.week
+    topic = Topic.create!(last_read: date)
+    assert_equal date, Topic.find(topic.id).last_read
+  end
+
+  def test_bc_date_leap_year
+    date = Time.utc(-4, 2, 29).to_date
+    topic = Topic.create!(last_read: date)
+    assert_equal date, Topic.find(topic.id).last_read
+  end
+
+  def test_bc_date_year_zero
+    date = Time.utc(0, 4, 7).to_date
+    topic = Topic.create!(last_read: date)
+    assert_equal date, Topic.find(topic.id).last_read
+  end
 end