Style/RedundantBegin should be marked as unsafe for auto-correction

[gPrado]

Style/RedundantBegin cop might auto-correct code incorrectly, leading to a performance issue or even a broken build. See example below:

---

Precondition

Given the following example class

class Test
  def initialize
    @first_run = false
  end

  def memoized
    @memoized ||= begin
      'memoized' if first_run
    end
  end

  def first_run
    # this might be an expensive operation
    fail 'already run!' if @first_run

    @first_run = true
  end
end

and the following test code:

test = Test.new
2.times { test.memoized }

Expected behavior

The code should not be auto-corrected, or maybe auto-corrected as the following:

class Test
  def initialize
    @first_run = false
  end

  def memoized
    @memoized ||= ('memoized' if first_run)
  end

  def first_run
    # this might be an expensive operation
    fail 'already run!' if @first_run

    @first_run = true
  end
end

Actual behavior

The code is auto-corrected as follows:

class Test
  def initialize
    @first_run = false
  end

  def memoized
    @memoized ||= 'memoized' if first_run
  end

  def first_run
    # this might be an expensive operation
    fail 'already run!' if @first_run

    @first_run = true
  end
end

which makes the test code raise an exception.

RuboCop version

1.12.1 (using Parser 3.0.1.0, rubocop-ast 1.4.1, running on ruby 2.6.6 x86_64-linux)

[koic]

Thank you for the feedback. This is an auto-correction bug, so I opened #9682 that it will be safe auto-corrected code.