Add new Performance/UriDefaultParser cop

[koic]

This cop is inspired by #4694 (comment).

Feature

This cop identifies places where URI::Parser.new can be replaced by URI::DEFAULT_PARSER.

% cat /tmp/test.rb
# frozen_string_literal: true

require 'uri'

URI::Parser.new.make_regexp

% bundle exec rubocop /tmp/test.rb
Inspecting 1 file
C

Offenses:

/tmp/test.rb:5:1: C: Use URI::DEFAULT_PARSER instead of URI::Parser.new.
URI::Parser.new.make_regexp
^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected

Target Problem

The following is a benchmark script.

require 'benchmark/ips'
require 'uri'

Benchmark.ips do |x|
  x.report('URI::Parser.new')     { URI::Parser.new }
  x.report('URI::DEFAULT_PARSER') { URI::DEFAULT_PARSER }
  x.compare!
end

It is the result of running the above benchmark script.

% ruby bench.rb
Warming up --------------------------------------
     URI::Parser.new    70.000  i/100ms
 URI::DEFAULT_PARSER   315.505k i/100ms
Calculating -------------------------------------
     URI::Parser.new    714.537  (± 4.2%) i/s -      3.570k in   5.005495s
 URI::DEFAULT_PARSER     10.950M (± 6.2%) i/s -     54.582M in   5.007247s

Comparison:
 URI::DEFAULT_PARSER: 10949722.8 i/s
     URI::Parser.new:      714.5 i/s - 15324.22x  slower

It is a constant as follows and it is fast because it does not instantiate every time.
https://github.com/ruby/ruby/blob/v2_4_1/lib/uri/common.rb#L22

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Used the same coding conventions as the rest of the project.
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• All tests(rake spec) are passing.
• The new code doesn't generate RuboCop offenses that are checked by rake internal_investigation.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[Drenmi]

15324.22x slower

😅

[bbatsov]

👍

[koic]

Thank you!