Enable Style/RedundantFetchBlock and autocorrect-all

[zzak]

As @natematykiewicz pointed out in #47307 there is a rubocop rule for this.

[natematykiewicz]

If nil is the default, you can just use [].

Suggested change

	_default_attributes.fetch(name.to_s, nil),
	_default_attributes[name.to_s],

[zzak]

@natematykiewicz Thank you, but I don't think we should change this yet unless there is a specific rule we can apply that supports it. I'd like to avoid making cosmetic changes without a "failing" case.

[natematykiewicz]

I see you closed it because there's not a good way to differentiate Rails.cache from Hash. Makes sense. It's still possible this specific line using [] would be a performance change and not a cosmetic one. But you'd need a benchmark to see if it's actually faster.

[zzak]

Yes, that is solving a different problem. Feel free to open a PR with benchmarks 🙏

[zzak]

There's a bunch of related failures that should be fixed too:

ActiveSupport::Cache::RedisCacheStoreTests::FailureSafetyFromUnavailableClientTest#test_fetch_read_failure_does_not_attempt_to_write:
--
  | TypeError: no implicit conversion of Symbol into Integer
  | /rails/activesupport/lib/active_support/cache.rb:380:in `[]'
  | /rails/activesupport/lib/active_support/cache.rb:380:in `fetch'
  | /rails/activesupport/test/cache/behaviors/failure_safety_behavior.rb:19:in `block in test_fetch_read_failure_does_not_attempt_to_write'
  | /rails/activesupport/test/cache/stores/redis_cache_store_test.rb:370:in `emulating_unavailability'

Probably this change was too aggressive 🤔

[zzak]

Ok, TIL the reason for all of the Active Support failures is because it's calling ActiveSupport::Cache::Store#fetch which is completely different: https://edgeapi.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-fetch

After looking into this further it looks like this was already discussed on rubocop/rubocop#8196, and a previous attempt was made in #39765.

I think because we're required to rubocop:disable, until there is an alternative we cannot enable this rule.