Association loading isn't to be affected by scoping consistently

Follow-up of 5c71000, #29834, and #30271.

Currently, preloading and eager loading are not to be affected by
scoping, with the exception of `unscoped`.

But non eager loaded association access is still affected by scoping.

Although this is a breaking change, the association loading will work
consistently whether preloaded / eager loaded or not.

Before:

```ruby
Post.where("1=0").scoping do
  Comment.find(1).post                   # => nil
  Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
  Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>
end
```

After:

```ruby
Post.where("1=0").scoping do
  Comment.find(1).post                   # => #<Post id: 1, ...>
  Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
  Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>
end
```

Fixes #34638.
Fixes #35398.

1 files changed, 27 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index f0396c3d53..08f44e0b91 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,30 @@
+*   Association loading isn't to be affected by scoping consistently
+    whether preloaded / eager loaded or not, with the exception of `unscoped`.
+
+    Before:
+
+    ```ruby
+    Post.where("1=0").scoping do
+      Comment.find(1).post                   # => nil
+      Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
+      Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>
+    end
+    ```
+
+    After:
+
+    ```ruby
+    Post.where("1=0").scoping do
+      Comment.find(1).post                   # => #<Post id: 1, ...>
+      Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
+      Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>
+    end
+    ```
+
+    Fixes #34638, #35398.
+
+    *Ryuta Kamizono*
+
 *   Add `rails db:prepare` to migrate or setup a database.
 
     Runs `db:migrate` if the database exists or `db:setup` if it doesn't.