Deprecate `where.not` working as NOR and will be changed to NAND in Rails 6.1

`where.not` with polymorphic association is partly fixed incidentally at
213796f (refer #33493, #26207, #17010, #16983, #14161), and I've added
test case e9ba12f to avoid lose that fix accidentally in the future.

In Rails 5.2, `where.not(polymorphic: object)` works as expected as
NAND, but `where.not(polymorphic_type: object.class.polymorphic_name,
polymorphic_id: object.id)` still unexpectedly works as NOR.

To will make `where.not` working desiredly as NAND in Rails 6.1, this
deprecates `where.not` working as NOR. If people want to continue NOR
conditions, we'd encourage to them to `where.not` each conditions
manually.

```ruby
all = [treasures(:diamond), treasures(:sapphire), cars(:honda), treasures(:sapphire)]
assert_equal all, PriceEstimate.all.map(&:estimate_of)
```

In Rails 6.0:

```ruby
sapphire = treasures(:sapphire)

nor = all.reject { |e|
  e.estimate_of_type == sapphire.class.polymorphic_name
}.reject { |e|
  e.estimate_of_id == sapphire.id
}
assert_equal [cars(:honda)], nor

without_sapphire = PriceEstimate.where.not(
  estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
)
assert_equal nor, without_sapphire.map(&:estimate_of)
```

In Rails 6.1:

```ruby
sapphire = treasures(:sapphire)

nand = all - [sapphire]
assert_equal [treasures(:diamond), cars(:honda)], nand

without_sapphire = PriceEstimate.where.not(
  estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
)
assert_equal nand, without_sapphire.map(&:estimate_of)
```

Resolves #31209.

2 files changed, 51 insertions, 6 deletions

diff --git a/activerecord/test/cases/relation/where_clause_test.rb b/activerecord/test/cases/relation/where_clause_test.rb
index 0b06cec40b..b26a1a1d80 100644
--- a/activerecord/test/cases/relation/where_clause_test.rb
+++ b/activerecord/test/cases/relation/where_clause_test.rb
@@ -106,7 +106,7 @@ class ActiveRecord::Relation
         Arel::Nodes::Not.new(random_object)
       ])
 
-      assert_equal expected, original.invert
+      assert_equal expected, original.invert(:nor)
     end
 
     test "except removes binary predicates referencing a given column" do
diff --git a/activerecord/test/cases/relation/where_test.rb b/activerecord/test/cases/relation/where_test.rb
index b045184d7d..2ecccfe1f3 100644
--- a/activerecord/test/cases/relation/where_test.rb
+++ b/activerecord/test/cases/relation/where_test.rb
@@ -115,13 +115,58 @@ module ActiveRecord
       assert_equal expected.to_sql, actual.to_sql
     end
 
-    def test_polymorphic_shallow_where_not
-      treasure = treasures(:sapphire)
+    def test_where_not_polymorphic_association
+      sapphire = treasures(:sapphire)
 
-      expected = [price_estimates(:diamond), price_estimates(:honda)]
-      actual   = PriceEstimate.where.not(estimate_of: treasure)
+      all = [treasures(:diamond), sapphire, cars(:honda), sapphire]
+      assert_equal all, PriceEstimate.all.sort_by(&:id).map(&:estimate_of)
 
-      assert_equal expected.sort_by(&:id), actual.sort_by(&:id)
+      actual = PriceEstimate.where.not(estimate_of: sapphire)
+      only = PriceEstimate.where(estimate_of: sapphire)
+
+      expected = all - [sapphire]
+      assert_equal expected, actual.sort_by(&:id).map(&:estimate_of)
+      assert_equal all - expected, only.sort_by(&:id).map(&:estimate_of)
+    end
+
+    def test_where_not_polymorphic_id_and_type_as_nand
+      sapphire = treasures(:sapphire)
+
+      all = [treasures(:diamond), sapphire, cars(:honda), sapphire]
+      assert_equal all, PriceEstimate.all.sort_by(&:id).map(&:estimate_of)
+
+      actual = PriceEstimate.where.yield_self do |where_chain|
+        where_chain.stub(:not_behaves_as_nor?, false) do
+          where_chain.not(estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id)
+        end
+      end
+      only = PriceEstimate.where(estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id)
+
+      expected = all - [sapphire]
+      assert_equal expected, actual.sort_by(&:id).map(&:estimate_of)
+      assert_equal all - expected, only.sort_by(&:id).map(&:estimate_of)
+    end
+
+    def test_where_not_polymorphic_id_and_type_as_nor_is_deprecated
+      sapphire = treasures(:sapphire)
+
+      all = [treasures(:diamond), sapphire, cars(:honda), sapphire]
+      assert_equal all, PriceEstimate.all.sort_by(&:id).map(&:estimate_of)
+
+      message = <<~MSG.squish
+        NOT conditions will no longer behave as NOR in Rails 6.1.
+        To continue using NOR conditions, NOT each conditions manually
+        (`.where.not(:estimate_of_type => ...).where.not(:estimate_of_id => ...)`).
+      MSG
+      actual = assert_deprecated(message) do
+        PriceEstimate.where.not(estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id)
+      end
+      only = PriceEstimate.where(estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id)
+
+      expected = all - [sapphire]
+      # NOT (estimate_of_type = 'Treasure' OR estimate_of_id = sapphire.id) matches only `cars(:honda)` unfortunately.
+      assert_not_equal expected, actual.sort_by(&:id).map(&:estimate_of)
+      assert_equal all - expected, only.sort_by(&:id).map(&:estimate_of)
     end
 
     def test_polymorphic_nested_array_where