Add new Lint/NonAtomicFileOperation cop

[ydah]

This PR is add new Lint/NonAtomicFileOperation cop

Checks for non-atomic file operations.
And then replace it with a nearly equivalent and atomic method.

These can cause problems that are difficult to reproduce, especially in cases of frequent file operations in parallel, such as test runs with parallel_rspec.

For examples: creating a directory if there is none, has the following problems

An exception occurs when the directory didn't exist at the time of exist?, but someone else created it before mkdir was executed.

Subsequent processes are executed without the directory that should be there when the directory existed at the time of exist?, but someone else deleted it shortly afterwards.

@safety

This cop is unsafe, because autocorrection change to atomic processing.
The atomic processing of the replacement destination is not guaranteed to be strictly equivalent to that before the replacement.

@example

# bad
unless FileTest.exist?(path)
  FileUtils.makedirs(path)
end

if FileTest.exist?(path)
  FileUtils.remove(path)
end

# good
FileUtils.mkdir_p(path)

FileUtils.rm_rf(path)

---

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.

[bbatsov]

In this case the Redundant check is actually Dangerous if you ask me, so perhaps we can rename the cop accordingly. Something like NonAtomicFileOperation might also be appropriate IMO. @rubocop/rubocop-core what do you think?

P.S. Naming is still hard! :D

[ydah]

Naming always annoys me for a long time...
I feel that NonAtomicFileOperation looks good and I changed it. What do you think?

[bbatsov]

It's fine by me, but I'll leave this open for a couple of days to see if some of the other maintainers comes up with a better name.

It'd be nice if we also mention this in the Ruby style guide, as I doubt many people are aware of this problem.

[mathieujobin]

this new cop makes my rubocop crash...
on both 1.30.0 and 1.30.1

[koic]

@mathieujobin Can you open a new issue with the bug report template?
https://github.com/rubocop/rubocop/issues/new/choose