Actually `index_name_length` depend on `max_identifier_length`, not
always 63.

Deprecate `supports_migrations?` on connection adapters

Refactor connection_pool_test

`supports_migrations?` was added at 4160b518 to determine if schema
statements (`create_table`, `drop_table`, etc) are implemented in the
adapter. But all tested databases has been supported migrations since
a4fc93c3 at least.

Include selects in group query with having clause

When a grouped calculation contains a having clause that references a
selected value, we need to include that selected value in the query.

Postgres doesn't support referencing a selected value in a having
clause, but other databases do; we can skip the test on the pg adapter
but run it for the others.

This was fixed before in 9a298a16, but
the test coverage was lost in 5a05207d.
The fix regressed in 6311975f and was
removed in 97d46c17.

Remove unused params in RouteSet#add_route

Push `valid_type?` up to abstract adapter

Remove duplicated private method in ActiveRecord::FinderMethods

Remove useless `select_values += select_values`

Use released arel

Follow up to ea9566f6

`select_values` is a local variable defined at previous line.
`select_values += select_values` is totally useless.

It's common in test cases at my job to have code like this:

    let(:today) { customer_start_date + 2.weeks }
    let(:earlier_date) { today - 5.days }

With this change, we can instead write

    let(:today) { 2.weeks.after(customer_start_date) }
    let(:earlier_date) { 5.days.before(today) }

Closes #27721

`valid_type?` should return true if a type exists in
`native_database_types` at least.

https://github.com/rails/rails/blob/v5.1.0.beta1/activerecord/lib/active_record/schema_dumper.rb#L136

Fix typo 'affect' -> 'effect' [ci skip]

Currently `change_column` cannot drop default if `null: false` is
specified at the same time. This change fixes the issue.

```ruby
  # cannot drop default
  change_column "tests", "contributor", :boolean, default: nil, null: false

  # we need the following workaround currently
  change_column "tests", "contributor", :boolean, null: false
  change_column "tests", "contributor", :boolean, default: nil
```

Closes #26582

AS CHANGELOG Pass 

Deprecate AbstractAdapter#verify! with arguments

Use ensure block for things we cleanup in tests

`DISTINCT` clause is applied inside aggregate function by
`operation_over_aggregate_column` if needed. Unneeded outside aggregate
function.

```ruby
  # Before
  author.unique_categorized_posts.count
  # => SELECT DISTINCT COUNT(DISTINCT "posts"."id") FROM "posts" INNER JOIN "categorizations" ON "posts"."id" = "categorizations"."post_id" WHERE "categorizations"."author_id" = ?  [["author_id", 2]]

  # After
  author.unique_categorized_posts.count
  # => SELECT COUNT(DISTINCT "posts"."id") FROM "posts" INNER JOIN "categorizations" ON "posts"."id" = "categorizations"."post_id" WHERE "categorizations"."author_id" = ?  [["author_id", 2]]
```

Closes #27615

In ca324a0d the flash middleware was effectively removed by its
constructor returning the app it was passed and the `commit_flash`
call was moved to the `ActionController::Metal#dispatch` method.
This broke any redirect routes that modified the flash because the
redirect happens before `dispatch` gets called.

To fix it, this commit adds a `commit_flash` call in the `serve`
method of `ActionDispatch::Routing::Redirect`.

Fixes #27992.

Improve docs for Rails::AppGenerator. [ci skip]

Add example so its easier to understand how one can overide
an app generator.

[close #24435] Send user_supplied_options to server

Closes #27429

In Ruby 2.4, BigDecimal(), as used by the Decimal cast, was changed so
that it will raise ArgumentError when passed an invalid string, in order
to be more consistent with Integer(), Float(), etc. The other numeric
types use ex. to_i and to_f.

Unfortunately, we can't simply change BigDecimal() to to_d. String#to_d
raises errors like BigDecimal(), unlike all the other to_* methods (this
should probably be filed as a ruby bug).

Instead, this simulates the existing behaviour and the behaviour of the
other to_* methods by finding a numeric string at the start of the
passed in value, and parsing that using BigDecimal().

See also
https://bugs.ruby-lang.org/issues/10286
https://github.com/ruby/bigdecimal/commit/3081a627cebdc1fc119425c7a9f009dbb6bec8e8