Fix false positive for Style/EmptyLineAfterGuardClause

[koic]

Related #5679.

This PR fixes a false positive for Style/EmptyLineAfterGuardClause when guard clause is after heredoc.

Reproduction code

def foo
  raise ArgumentError, <<-MSG unless path
    Must be called with mount point
  MSG

  bar
end

📝 I found this false positivity below.
https://github.com/rails/rails/blob/v5.2.0.rc2/actionpack/lib/action_dispatch/routing/mapper.rb#L614-L622

Expected behavior

No offenses.

Actual behavior and Steps to reproduce the problem

% rubocop /tmp/example.rb --only Style/EmptyLineAfterGuardClause
Inspecting 1 file
C

Offenses:

/tmp/example.rb:2:3: C: Style/EmptyLineAfterGuardClause: Add empty line
after guard clause.
  raise ArgumentError, <<-MSG unless path
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected

RuboCop version

% rubocop -V
0.54.0 (using Parser 2.5.0.4, running on ruby 2.5.0 x86_64-darwin17)

This PR fixes the above false positive.

---

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[pocke]

I guess thsi cop also allows the following code.

def foo
  raise ArgumentError, <<-MSG unless path
    Must be called with mount point
  MSG
  bar
end

Should the cop allow it? I guess the cop should add an offense to the code since there are no new lines between the guard clause and the next statement. But it is an exceptional case, so I'm not sure should the cop do.

I think we should decide the behaviour, and add a test case for this code.

[bbatsov]

Guard clauses after heredocs are extremely hard to spot IMO. I wonder if it would be wise to discourage those.

As for this example - it seems to me there should be some blank line in this case.

[Drenmi]

I guess the cop should add an offense to the code since there are no new lines between the guard clause and the next statement.

I agree.

[Drenmi]

I also noticed this cop has been placed in the wrong namespace. Should be in Layout with the other EmptyLine* cops. 🙂

[koic]

I also think the example code @pocke showed is false negative. I'll look it in detail later.
Apart from that, this PR shows the value to fix the problem that autocorrect breaks heredoc.

I also noticed this cop has been placed in the wrong namespace. Should be in Layout with the other EmptyLine* cops.

Yep. I think so too. Certainly this cop will not be Style department but Layout department 👍
However, it is different from the purpose I'd like to accomplish by this PR. So it will be another PR.