Style/FetchEnvVar check for if condition

[ShockwaveNN]

Not sure that rubocop can check it or dynamic check is required for such checks, but I'll report it anyway

Steps to reproduce the problem

1. Create test.rb with content:

# frozen_string_literal: true

if ENV['foo']
  puts 'some code'
  puts ENV['foo']
  puts 'other code'
end

2. run rubocop -A check
   result code will be:

# frozen_string_literal: true
    
if ENV['foo']
  puts 'some code'
  puts ENV.fetch('foo', nil)
  puts 'other code'
end

So fetch is literally useless in code like this

RuboCop version

$ [bundle exec] rubocop -V
1.28.1 (using Parser 3.1.2.0, rubocop-ast 1.17.0, running on ruby 3.1.2 x86_64-linux)
  - rubocop-performance 1.13.3

[ShockwaveNN]

But in same time there may be code like this:

if ENV['foo']
  ENV.delete('foo')
  puts 'some code'
  puts ENV['foo']
  puts 'other code'
end

And fetch is required in this code, so I'm thinking that correct check via rubocop in cases like this cannot be done

[rthornton128]

ENV['foo'], ENV.fetch('foo', nil) and ENV.dig('foo') are all functionally equivalent. All three return nil when ENV does not contain the matching key. Perhaps what this cop should state, when recommending ENV.fetch('foo', nil) as an alternative, is the explicitness of returning nil?

Ultimately, a developer/team/project is free to ignore or disable cops. We should not blindly use all of them. If we think the cop has no value or does not apply to our code base, we should disable them. I think that applies to this case.

EDIT: Misread the issue.