Use `count(:all)` in HasManyAssociation#count_records

Problem: Calling `count` on an association can cause invalid SQL queries
to be created where the `SELECT COUNT(a, b, c)` function receives
multiple  columns. This will cause a `StatementInvalid` exception later
on.

Solution: Use `count(:all)`, which generates a `SELECT COUNT(*)...`
query independently of the association.

This also includes a test case that, before the fix, broke.

2 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index cbecfa84ff..df75776254 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -2446,6 +2446,14 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal [first_bulb, second_bulb], car.bulbs
   end
 
+  test "association size calculation works with default scoped selects when not previously fetched" do
+    firm = Firm.create!(name: "Firm")
+    5.times { firm.developers_with_select << Developer.create!(name: "Developer") }
+
+    same_firm = Firm.find(firm.id)
+    assert_equal 5, same_firm.developers_with_select.size
+  end
+
   test "double insertion of new object to association when same association used in the after create callback of a new object" do
     reset_callbacks(:save, Bulb) do
       Bulb.after_save { |record| record.car.bulbs.load }
diff --git a/activerecord/test/models/company.rb b/activerecord/test/models/company.rb
index 20e37710e7..7ab969cdf1 100644
--- a/activerecord/test/models/company.rb
+++ b/activerecord/test/models/company.rb
@@ -85,6 +85,8 @@ class Firm < Company
 
   has_many :association_with_references, -> { references(:foo) }, class_name: "Client"
 
+  has_many :developers_with_select, -> { select("id, name, first_name") }, class_name: "Developer"
+
   has_one :lead_developer, class_name: "Developer"
   has_many :projects