[Fix #171] Extend auto-correction support for Performance/Sum

[koic]

Fixes #171.

This PR makes Performance/Sum cop can be changed auto-correction scope depending on the value of SafeAutoCorrect in .rubocop.yml.

Its auto-correction is marked as safe by default (SafeAutoCorrect: true) to prevent TypeError in auto-correced code when initial value is not specified as shown below:

['a', 'b'].sum # => (String can't be coerced into Integer)

Therefore if initial value is not specify as in that code, it will not be auto-corrected.

If user always want to enable auto-correction, user can set SafeAutoCorrect: false.

Performance/Sum:
  SafeAutoCorrect: false

SafeAutoCorrect remains true by default, so the behavior does not change.

---

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[koic]

@rubocop-hq/rubocop-core User can change auto-correction behaviour by specifying from SafeAutoCorrect: true (default) to SafeAutoCorrect: false in .rubocop.yml. That may be an unprecedented (or unexpected) usage. If you have any concerns about using the SafeAutoCorrect option, please comment your feedback.

[marcandre]

I'd like to know why you are proposing this instead of marking this cop as SafeAutoCorrect: false?

[marcandre]

Oh, sorry, I understand that you want the safe autocorrection to be always done.

It would be better if add_offense accepted a parameter to say "this one is safe to auto-correct"

[koic]

Thank you for your feedback. I can probably add to the doc about always safe auto-correction cases.
Is there anything I need to update about this PR's implementation? I'm sorry for my lack of understanding 💦

[marcandre]

Actually, I like your implementation.

I think it we should have better support for this kind of cop. Maybe this cop could specify: SafeAutoCorrect: both?

[koic]

Thank you for supplementing. I only saw it from one perspective, you've made me realize there's other perspectives to this 😅
Currently only SafeAutoCorrect: true and SafeAutoCorrect: false are supported by core, so I'd like to start with this boolean toggle first.