Do a check if the 'rel' argument is passed in, and simply set it to
'nofollow' if 'rel' was not passed in. This prevents three string
allocations for each call to `link_to` in that scenario. In the scenario
where the 'rel' argument is passed in, performance is around the same as
before as the `key?` check is very fast.

```ruby
begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update
                your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  gem "benchmark-ips"
  gem "rails"
end

def allocate_count
  GC.disable
  before = ObjectSpace.count_objects
  yield
  after = ObjectSpace.count_objects
  after.each { |k,v| after[k] = v - before[k] }
  after[:T_HASH] -= 1 # probe effect - we created the before hash.
  GC.enable
  result = after.reject { |k,v| v == 0 }
  GC.start
  result
end

@hash = {}

def master_version
  "#{@hash['rel'.freeze]} nofollow".lstrip
end

def fast_version
  if @hash.key?('rel'.freeze)
    "#{@hash["rel"]} nofollow".lstrip
  else
    "nofollow".freeze
  end
end

puts 'no rel key'

puts "master_version"
puts allocate_count { 1000.times { master_version } }
puts "fast_version"
puts allocate_count { 1000.times { fast_version } }

Benchmark.ips do |x|
  x.report("master_version") { master_version }
  x.report("fast_version")     { fast_version }
  x.compare!
end

puts 'rel key'

@hash['rel'] = 'hi'.freeze

puts "master_version"
puts allocate_count { 1000.times { master_version } }
puts "fast_version"
puts allocate_count { 1000.times { fast_version } }

Benchmark.ips do |x|
  x.report("master_version") { master_version }
  x.report("fast_version")     { fast_version }
  x.compare!
end
```

```
no rel key
master_version
{:FREE=>-2791, :T_STRING=>3052}
fast_version
{:FREE=>-1}
Warming up --------------------------------------
      master_version    80.324k i/100ms
        fast_version   200.262k i/100ms
Calculating -------------------------------------
      master_version      2.049M (±11.9%) i/s -     10.121M in   5.025613s
        fast_version      6.645M (±21.3%) i/s -     29.439M in   5.007488s

Comparison:
        fast_version:  6644506.3 i/s
      master_version:  2048833.0 i/s - 3.24x  slower

rel key
master_version
{:FREE=>-2001, :T_STRING=>2000}
fast_version
{:FREE=>-2001, :T_STRING=>2000}
Warming up --------------------------------------
      master_version   155.673k i/100ms
        fast_version   106.515k i/100ms
Calculating -------------------------------------
      master_version      2.652M (±20.4%) i/s -     12.610M in   5.036494s
        fast_version      2.237M (±16.8%) i/s -     10.865M in   5.035366s

Comparison:
      master_version:  2651702.2 i/s
        fast_version:  2237470.6 i/s - same-ish: difference falls within error
```

delegate scope_for on PolymorphicReflection

fix initial count

Allow passing a Proc or Symbol as an argument to length validator values

This brings the Length validator in line with the Numericality
validator, which currently supports Proc & Symbol arguments

Remove mention about Evented Redis [ci skip]

Evented Redis adapter was removed in 48766e32.

remove incorrect comment about serializable transactions [ci skip]

using serializable isolation would prevent the duplicate insert as done in the example from happening

Remove unused `secrets.yml` template

Move `extensions` to `PostgreSQL::SchemaDumper`

- Backport commit: https://github.com/rails/rails/commit/7122a2cdc3634e170129f8b6cabd1e8fbed13c3d

Wrap accepted nested attributes params

to properly wrap all attributes, including those which are nested.

and abstract `SchemaDumper#extensions` is now an empty method.

Since #30337, every database adapter has its own `SchemaDumper`.
`extensions` are only supported by PostgreSQL database and postgresql database adapter.

Save index order :desc to schema.rb (sqlite). Fixes #30902

[ci skip]Add space before closing curly brace

Does not include disabled element in params

Change `VENDOR_PATH` to `APP_ROOT` in `bin/yarn`

This variable was initially used to hold the vendor directory.
https://github.com/rails/rails/commit/3dac36b

Therefore, the variable name `VENDOR_PATH` was appropriate.
However, `package.json` is now placed in the root of the project.
https://github.com/rails/rails/commit/8e9e943

Therefore, like other bin scripts, I think the variable name `APP_ROOT`
is appropriate.
https://github.com/rails/rails/blob/2c845f6b03ddf2aa233b00385d24d769a4a34fa6/railties/lib/rails/generators/rails/app/templates/bin/setup.tt#L5
https://github.com/rails/rails/blob/2c845f6b03ddf2aa233b00385d24d769a4a34fa6/railties/lib/rails/generators/rails/app/templates/bin/update.tt#L5

`supports_extensions?` return always true since PostgreSQL 9.1

since the minimum version of PostgreSQL currently Rails supports is 9.1,
there is no need to handle if `supports_extensions?`

Refer https://www.postgresql.org/docs/9.1/static/sql-createextension.html
"CREATE EXTENSION"

Simplify API documentation of methods that return a Duration

Related to #30972

Make clear that Time core extensions are split between Numeric and Integer

Although the sqlite adapter supports index sort orders, they
weren't being written to db/schema.rb.

Space between { and | missing.

The documentation wrongly suggests that Time extensions to Numeric include
methods months and years, when these belong to Integer.

Update both classes and guides.

Currently alias tracker only refer a table name, doesn't respect an
alias name. Should use `join.left.name` rather than
`join.left.table_name`.

Improve a code style recommendation following Rubocop instructions https://codeclimate.com/github/rails/rails/issues

Remove `supports_disable_referential_integrity?`

`supports_disable_referential_integrity?` used to handle
if PostgreSQL database supports
`ALTER TABLE <table name> DISABLE/ENABLE TRIGGER` statements.
Refer https://github.com/rails/rails/commit/9a947af0e79cfb8692eb7e5ae94c1b8c40756f49

These statements have been documented since 8.1.

https://www.postgresql.org/docs/8.1/static/sql-altertable.html
> DISABLE/ENABLE TRIGGER

Now Rails supports PostgreSQL 9.1 or higher only.
No need to handle `supports_disable_referential_integrity?` anymore.
Also, this method does not exist in any other adapters including AbstractAdapter.