Make `reflection.klass` raise if `polymorphic?` not to be misused

This is an alternative of #31877 to fix #31876 caused by #28808.

This issue was caused by a combination of several loose implementation.

* finding automatic inverse association of polymorphic without context (caused by #28808)
* returning `klass` even if `polymorphic?` (exists before #28808)
* loose verification by `valid_inverse_reflection?` (exists before #28808)

This makes `klass` raise if `polymorphic?` not to be misused.
This issue will not happen unless polymorphic `klass` is misused.

Fixes #31876.
Closes #31877.

1 files changed, 2 insertions, 0 deletions

diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 7d008eecd5..3f4fe16678 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -814,6 +814,7 @@ ActiveRecord::Schema.define do
   create_table :sponsors, force: true do |t|
     t.integer :club_id
     t.references :sponsorable, polymorphic: true, index: false
+    t.references :sponsor, polymorphic: true, index: false
   end
 
   create_table :string_key_objects, id: false, force: true do |t|
@@ -951,6 +952,7 @@ ActiveRecord::Schema.define do
     t.string  :poly_man_without_inverse_type
     t.integer :horrible_polymorphic_man_id
     t.string  :horrible_polymorphic_man_type
+    t.references :human, polymorphic: true, index: false
   end
 
   create_table :interests, force: true do |t|