A query may wait on a database-level lock, which could lead to a
deadlock between threads.

Following off of https://github.com/rails/rails/issues/15945, I realized that super
needs to be the first thing that is called in an AbstractModel's inherited method.
I was receiving errors within the inherited method of time_zone_conversion, so I tested
locally by moving super to the top of the method declaration. All exceptions went away.

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.

This executor currently relies on `ActiveRecord::Base.connection` not
changing between `prepare` and `complete`. If something else returns
the current ActiveRecord connection to the pool early then this
`complete` call will fail to clear the correct query cache and restore
the original `query_cache_enabled` status.

This has for example been happening in Sidekiq:

     https://github.com/mperham/sidekiq/pull/3166

We can just keep track of the connection as part of the exector state.

Follow up to 99cf7558.

* Put a blank line after :call-seq: otherwise it will think the whole test
is the call seq.
* Improve some text.
* Use some rdoc formatting.
* Restores the documentation of table_name_prefix.

[ci skip]

[ci skip]

- These tests were fixed earlier on master in https://github.com/rails/rails/commit/f13ec72664fd13d33d617103ca964a7592295854.
- They started failing in first place due to change in https://github.com/brianmario/mysql2/commit/f14023fcfee9e85e6fc1b0e568048811518f8c23.
- They will fail again when the message is changed in mysql2 so let's
  not rely on the error message.

[ci skip]
Follow #26050

This reverts commit 671eb742.

This is not a change we would like moving forward.

- 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`.

Query cache doesn't type cast bind parameters since it isn't
actually querying the database, so it can't pass those values in.  Type
casting in the query cache method would cause the values to be type cast
twice in the case that there is a cache miss (since the methods it calls
will type cast *again*).  If logging is disabled, then adding the type
cast code to the query cache method will needlessly typecast the values
(since the only reason those values are type cast is for display in the
logs).

Fixes #26828.

This commit fixes the generated HTML of the two code examples.

Follow up to #20018.

MySQL 8.0.0-dmr `SUB_PART` column of `information_schema.statistics`
changed to varbinary(12), which is bigint(3) in MySQL 5.6.

Addresses #26774

If does not quote table name properly, invalid SQL is generated.

```
test/cases/adapters/postgresql/case_insensitive_test.rb:12: warning: ambiguous first argument; put parentheses or a space even after `/' operator
test/cases/adapters/postgresql/case_insensitive_test.rb:16: warning: ambiguous first argument; put parentheses or a space even after `/' operator
test/cases/adapters/postgresql/case_insensitive_test.rb:20: warning: ambiguous first argument; put parentheses or a space even after `/' operator
test/cases/adapters/postgresql/case_insensitive_test.rb:24: warning: ambiguous first argument; put parentheses or a space even after `/' operator
```

Follow up to #26735.

If `table_options` returns `{ comment: nil }`, `create_table` line is
broken.

Example:

```ruby
  create_table "accounts", force: :cascade,  do |t|
```

`migration_keys` includes `name` but `name` is not a column option.

```ruby
  # Before
  t.index ["firm_id", "type", "rating"], name: "company_index", order: {"rating"=>:desc}, using: :btree

  # After
  t.index ["firm_id", "type", "rating"], name: "company_index", order: { rating: :desc }, using: :btree
```

Currently blank comment does not dump to `db/schema.rb`. But created it
even if specified blank.

https://bugs.ruby-lang.org/issues/12739

ActiveModel::Type)

Some code was previously referring to ActiveModel::Type::*. This could
cause issues in the future if any of the ActiveRecord::Type classes were
overridden in the future.

`ActiveRecord::Type::Value`

This is now defined in
`ActiveModel::Type::Value` (`ActiveRecord::Type::Value` still exists but
it's effectively an alias)

Currently all adapters (postgresql, mysql2, sqlite3, oracle-enhanced,
and sqlserver) implemented `indexes` and schema dumper expects
implemented `indexes`.

https://github.com/rails/rails/blob/v5.0.0/activerecord/lib/active_record/schema_dumper.rb#L208

Therefore `respond_to?(:indexes)` checking is unnecessary.