The datetime precision with zero should be dumped

`precision: 0` was not dumped by f1a0fa9e19b7e4ccaea191fc6cf0613880222ee7.
However, `precision: 0` is valid value for PostgreSQL timestamps.

activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb

@@ -29,7 +29,7 @@ def prepare_column_options(column)
 
         limit = column.limit || native_database_types[column.type][:limit]
         spec[:limit]     = limit.inspect if limit
-        spec[:precision] = column.precision.inspect if column.precision && column.precision != 0
+        spec[:precision] = column.precision.inspect if column.precision
         spec[:scale]     = column.scale.inspect if column.scale
 
         default = schema_default(column) if column.has_default?

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -73,6 +73,12 @@ def column_spec_for_primary_key(column)
         spec
       end
 
+      def prepare_column_options(column)
+        spec = super
+        spec.delete(:precision) if column.type == :datetime && column.precision == 0
+        spec
+      end
+
       class Column < ConnectionAdapters::Column # :nodoc:
         delegate :strict, :collation, :extra, to: :sql_type_metadata, allow_nil: true
 

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

@@ -1,4 +1,5 @@
 require 'cases/helper'
+require 'support/schema_dumping_helper'
 require 'models/developer'
 require 'models/topic'
 
@@ -46,8 +47,6 @@ def test_timestamp_with_zone_values_without_rails_time_zone_support
 class TimestampTest < ActiveRecord::TestCase
   fixtures :topics
 
-  class Foo < ActiveRecord::Base; end
-
   def test_group_by_date
     keys = Topic.group("date_trunc('month', created_at)").count.keys
     assert_operator keys.length, :>, 0
@@ -72,6 +71,35 @@ def test_save_infinity_and_beyond
     assert_equal(-1.0 / 0.0, d.updated_at)
   end
 
+  def test_bc_timestamp
+    date = Date.new(0) - 1.week
+    Developer.create!(:name => "aaron", :updated_at => date)
+    assert_equal date, Developer.find_by_name("aaron").updated_at
+  end
+
+  def test_bc_timestamp_leap_year
+    date = Time.utc(-4, 2, 29)
+    Developer.create!(:name => "taihou", :updated_at => date)
+    assert_equal date, Developer.find_by_name("taihou").updated_at
+  end
+
+  def test_bc_timestamp_year_zero
+    date = Time.utc(0, 4, 7)
+    Developer.create!(:name => "yahagi", :updated_at => date)
+    assert_equal date, Developer.find_by_name("yahagi").updated_at
+  end
+end
+
+class TimestampPrecisionTest < ActiveRecord::TestCase
+  include SchemaDumpingHelper
+  self.use_transactional_fixtures = false
+
+  class Foo < ActiveRecord::Base; end
+
+  teardown do
+    ActiveRecord::Base.connection.drop_table(:foos, if_exists: true)
+  end
+
   def test_default_datetime_precision
     ActiveRecord::Base.connection.create_table(:foos)
     ActiveRecord::Base.connection.add_column :foos, :created_at, :datetime
@@ -119,24 +147,6 @@ def test_postgres_agrees_with_activerecord_about_precision
     assert_equal '4', pg_datetime_precision('foos', 'updated_at')
   end
 
-  def test_bc_timestamp
-    date = Date.new(0) - 1.week
-    Developer.create!(:name => "aaron", :updated_at => date)
-    assert_equal date, Developer.find_by_name("aaron").updated_at
-  end
-
-  def test_bc_timestamp_leap_year
-    date = Time.utc(-4, 2, 29)
-    Developer.create!(:name => "taihou", :updated_at => date)
-    assert_equal date, Developer.find_by_name("taihou").updated_at
-  end
-
-  def test_bc_timestamp_year_zero
-    date = Time.utc(0, 4, 7)
-    Developer.create!(:name => "yahagi", :updated_at => date)
-    assert_equal date, Developer.find_by_name("yahagi").updated_at
-  end
-
   def test_formatting_timestamp_according_to_precision
     ActiveRecord::Base.connection.create_table(:foos, force: true) do |t|
       t.datetime :created_at, precision: 0
@@ -150,8 +160,15 @@ def test_formatting_timestamp_according_to_precision
     assert_equal date.to_s, foo.updated_at.to_s
     assert_equal 000000, foo.created_at.usec
     assert_equal 999900, foo.updated_at.usec
-  ensure
-    ActiveRecord::Base.connection.drop_table(:foos, if_exists: true)
+  end
+
+  def test_datetime_precision_with_zero_should_be_dumped
+    ActiveRecord::Base.connection.create_table(:foos) do |t|
+      t.timestamps precision: 0
+    end
+    output = dump_table_schema("foos")
+    assert_match %r{t\.datetime\s+"created_at",\s+precision: 0,\s+null: false$}, output
+    assert_match %r{t\.datetime\s+"updated_at",\s+precision: 0,\s+null: false$}, output
   end
 
   private