Merge branch 'deprecate-calculations-with-block'

Follow up of the discussion from the original merge commit:
https://github.com/rails/rails/commit/f9cb645dfcb5cc89f59d2f8b58a019486c828c73#commitcomment-1414561

We want to avoid people's mistakes with methods like count and sum when
called with a block, that can easily lead to code performing poorly and
that could be way better written with a db query.

Please check the discussion there for more background.
Closes #8268

2 files changed, 10 insertions, 18 deletions

diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 01afa087be..6cdc166533 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1658,6 +1658,12 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_deprecated { klass.has_many :foo, :counter_sql => 'lol' }
   end
 
+  test "sum calculation with block for array compatibility is deprecated" do
+    assert_deprecated do
+      posts(:welcome).comments.sum { |c| c.id }
+    end
+  end
+
   test "has many associations on new records use null relations" do
     post = Post.new
 
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index 65d28ea028..5cb7eabf0e 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -383,30 +383,16 @@ class CalculationsTest < ActiveRecord::TestCase
         Company.where(:type => "Firm").from('companies').count(:type)
   end
 
-  def test_count_with_block_acts_as_array
-    accounts = Account.where('id > 0')
-    assert_equal Account.count, accounts.count { true }
-    assert_equal 0, accounts.count { false }
-    assert_equal Account.where('credit_limit > 50').size, accounts.count { |account| account.credit_limit > 50 }
-    assert_equal Account.count, Account.count { true }
-    assert_equal 0, Account.count { false }
-  end
-
-  def test_sum_with_block_acts_as_array
-    accounts = Account.where('id > 0')
-    assert_equal Account.sum(:credit_limit), accounts.sum { |account| account.credit_limit }
-    assert_equal Account.sum(:credit_limit) + Account.count, accounts.sum{ |account| account.credit_limit + 1 }
-    assert_equal 0, accounts.sum { |account| 0 }
-  end
-
   def test_sum_with_from_option
     assert_equal Account.sum(:credit_limit), Account.from('accounts').sum(:credit_limit)
     assert_equal Account.where("credit_limit > 50").sum(:credit_limit),
         Account.where("credit_limit > 50").from('accounts').sum(:credit_limit)
   end
 
-  def test_sum_array_compatibility
-    assert_equal Account.sum(:credit_limit), Account.sum(&:credit_limit)
+  def test_sum_array_compatibility_deprecation
+    assert_deprecated do
+      assert_equal Account.sum(:credit_limit), Account.sum(&:credit_limit)
+    end
   end
 
   def test_average_with_from_option