Using Constant and symbol class_name option for associations are valid but raises exception on HABTM associations.
There was a test case which tries to cover symbol class_name usage but doesn't cover correctly. Fixed both symbol usage and constant usage as well.

These are all working as expected now;
```
  has_and_belongs_to_many :foos, class_name: 'Foo'
  has_and_belongs_to_many :foos, class_name: :Foo
  has_and_belongs_to_many :foos, class_name: Foo
```

Closes #23767

Regexp#match? should be considered to be part of the Ruby core library. We are
emulating it for < 2.4, but not having to require the extension is part of the
illusion of the emulation.

- CollectionAssociation#select was removed in
  https://github.com/rails/rails/pull/25989 in favor of
  QueryMethods#select but it caused a regression when passing arguments
  to select and a block.
- This used to work earlier in Rails 4.2 and Rails 5. See gist
  https://gist.github.com/prathamesh-sonpatki/a7df922273473a77dfbc742a4be4b618.
- This commit restores the behavior of Rails 4.2 and Rails 5.0.0 to
  allow passing arguments and block at the same time but also deprecates
  it.
- Because, these arguments do not have any effect on the output of
  select when select is used with a block.
- Updated documentation to remove the example passing arguments and
  block at the same time to `CollectionProxy#select`.

This was caused by 6d0d83a3. While the
bug it's trying to fix is handled if the association is loaded in an
after_(create|save) callback, it doesn't handle any cases that load the
association before the persistence takes place (validation, or before_*
filters). Instead of caring about the timing of persistence, we can just
ensure that we're not double adding the record instead.

The test from that commit actually broke, but it was not because the bug
has been re-introduced. It was because `Bulb` in our test suite is doing
funky things that look like STI but isn't STI, so equality comparison
didn't happen as the loaded model was of a different class.

Fixes #26661.

assert [1, 3].includes?(2) fails with unhelpful "Asserting failed" message

assert_includes [1, 3], 2 fails with "Expected [1, 3] to include 2" which makes it easier to debug and more obvious what went wrong

If a parent association was accessed in an `after_find` or
`after_initialize` callback, it would always end up loading the
association, and then immediately overwriting the association we just
loaded. If this occurred in a way that the parent's `current_scope` was
set to eager load the child, this would result in an infinite loop and
eventually overflow the stack.

For records that are created with `.new`, we have a mechanism to
perform an action before the callbacks are run. I've introduced the same
code path for records created with `instantiate`, and updated all code
which sets inverse instances on newly loaded associations to use this
block instead.

Fixes #26320.

Previously, if the the association was previously loaded and then
the foreign key changed by itself, a #save call would trigger a
load of the new associated record during autosave. This is unnecessary
and the autosave code (in that case) didn't use the loaded record
anyways.

Otherwise CollectionProxy's bang methdos cannot respect dirty target.

`#second`, `#third`, etc finder methods was added in 03855e79.
But the signature of these methods is inconsistent with the original
finder methods. And also the signature of `#first` and `#last` methods
is different from the original. This commit fixes the inconsistency.

The current behaviour of checking if there is a LEFT OUTER JOIN arel
node to detect if we are doing eager_loading is wrong. This problem
wasn't frequent before as only some pretty specific cases would add
a LEFT OUTER JOIN arel node. However, the recent new feature
left_outer_joins also add this node and made this problem happen
frequently.

Since in the perform_calculation function, we don't have access to
eager_loading information, I had to extract the logic for the distinct
out to the calculate method.

As I was in the file for left_outer_join tests, I fixed a few that had
bugs and I replaced some that were really weak with something that
will catch more issues.

In relation tests, the first test I changed would have failed if it
had validated the hash returned by count instead of just checking how
many pairs were in it. This is because this merge of join currently
transforms the join node into an outer join node, which then made
count do a distinct. So before this change, the return was
{1=>1, 4=>1, 5=>1}.

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

`#first`, `#second`, ..., `#last` methods respects dirty target. But
`#take` doesn't respect it. This commit fixes the inconsistent behavior.

When calling association.find RecordNotFound is now raised with the same argument as when we do it in Record.find (primary_key, id and model).

Hash syntax auto-correcting breaks alignments. 411ccbda

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

Fixes #24093

These test cases tests exactly mutating loaded target.

This is not a test case.

Where appropriatei, prefer the more concise Regexp#match?,
String#include?, String#start_with?, or String#end_with?

Fixes #25732.

`AssociationQueryHandler` requires `association` initialized
`TableMetadata` even if `table_name == arel_table.name`.

Fixes #25689.

Actually schema dumper/creation supports composite primary key (#21614).
Therefore it should not show the warning about composite primary key in
connection adapter.

This change moves the warning to `AttributeMethods::PrimaryKey` and
suppress the warning for habtm join table.

Fixes #25388.

`construct_relation_for_association_calculations` pass a string value to
`construct_join_dependency` when setting a string value in `from`.
It should not pass a string value, but always `joins_values`.

Related #14834, #19452.

Fixes #24193.

Currently `exists?` does some hackery where it assumes that we can join
onto anything that we passed to `eager_load` or `includes`, which
doesn't work if we are joining onto a polymorphic association.

Actually figuring out if we want to include something would require
knowledge deep within the join dependency module, which is hard to pull
up. The simplest solution is just to pass a flag down that says we're
not actually going to try to eager load any of the data. It's not the
solution I'd like, but that code really needs to be untangled before we
can do much with it.

This is another attempt at 6d5b1fdf which should address the concerns
that led to reverting it in 4ecabed2.

Fixes #25128

Ruby 2.4 unifies Fixnum and Bignum into Integer: https://bugs.ruby-lang.org/issues/12005

* Forward compat with new unified Integer class in Ruby 2.4+.
* Backward compat with separate Fixnum/Bignum in Ruby 2.2 & 2.3.
* Drops needless Fixnum distinction in docs, preferring Integer.

The error message that we give today makes this error difficult to debug
if you receive it. I have no clue why we're printing the object ID of
the class (the commit doesn't give context), but I've left it as it was
deliberate.

* Fix undefined method `owners' for NullPreloader:Class

Fixing undefined method `owners' for
ActiveRecord::Associations::Preloader::NullPreloader:Class

* Use Ruby 1.9 hash format

Use Ruby 1.9 hash format

#24192

[Rafael Mendonça França + Ladislav Smola]

Closes #23934.

This is a forward port of ac832a43

Previously the scope of all associations with extensions were wrapped in
an instance dependent proc. This made it impossible to preload such
associations.