Add new Style/HashExcept cop

[koic]

This PR adds new Style/HashExcept cop.

This cop checks for usages of Hash#reject and Hash#select methods that can be replaced with Hash#except method.

This cop should only be enabled on Ruby version 3.0 or higher.
(Hash#except was added in Ruby 3.0.)

# bad
{foo: 1, bar: 2, baz: 3}.reject {|k, v| k == :bar }
{foo: 1, bar: 2, baz: 3}.select {|k, v| k != :bar }

# good
{foo: 1, bar: 2, baz: 3}.except(:bar)

cf. https://bugs.ruby-lang.org/issues/15822

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[marcandre]

You're fast 😆

Technically, it's only if using eql? that they are equivalent.

{0 => :foo}.except(0.0)
# => {0=>:foo}
{0 => :foo}.reject {|k, v| k == 0.0 }
# => {}

Maybe if running in safe mode we should be more careful, so k == :symbol and k.eql? 0 is ok but not k == var?

[koic]

Oh, I couldn't catch it! I prefer being safe, so I updated this PR that way! For safe detection, it is limited to commonly used string and symbol comparisons when used ==. Thank you always!

[bbatsov]

I think you forgot about filter, keep_if and delete_if. I don't use those Hash methods often, but I recall there were a ton of aliases there.

[koic]

I added filter method. On the other hand, delete_if and keep_if methods are not checked because they are incompatible with except method.

# except
h = {foo: 1, bar: 2, baz: 3}
=> {:foo=>1, :bar=>2, :baz=>3}
h.except(:bar)
=> {:foo=>1, :baz=>3}
h
=> {:foo=>1, :bar=>2, :baz=>3}

# delete_if
h = {foo: 1, bar: 2, baz: 3}
=> {:foo=>1, :bar=>2, :baz=>3}
h.delete_if {|k, v| k == :bar }
=> {:foo=>1, :baz=>3}
h
=> {:foo=>1, :baz=>3}

# keep_if
h = {foo: 1, bar: 2, baz: 3}
=> {:foo=>1, :bar=>2, :baz=>3}
h.keep_if {|k, v| k != :bar }
=> {:foo=>1, :baz=>3}
h
=> {:foo=>1, :baz=>3}

I updated documentation and test on this.

[bbatsov]

Thanks!

[luke-hill]

@koic Question about this new cop.

I've noticed this pulling through on ruby 2.7 - However it's pulling through as Rails/ - I'm guessing this method is something which was added to the raw ruby implementation in ruby 3.0 (Previously I'm guessing it was in AS?)

Just saw the ruby lang implementation for ruby 2.7 - So I'm just guessing this was in AS before that?