Remove Lint/InvalidCharacterLiteral cop

[deivid-rodriguez]

It is uncertain whether this cop is actually useful in any case. The
only use case raises a syntax error and the tests for it are pending.

$ echo "puts(? )" | bundle exec rubocop --stdin test.rb
Inspecting 1 file
E

Offenses:

test.rb:1:6: W: invalid character syntax; use ?\s
(Using Ruby 2.0 parser; configure using TargetRubyVersion parameter, under AllCops)
puts(? )
     ^^
test.rb:1:6: E: unexpected token tEH
(Using Ruby 2.0 parser; configure using TargetRubyVersion parameter, under AllCops)
puts(? )
     ^

1 file inspected, 2 offenses detected

$ bundle exec ruby -e "puts(? )"
-e:1: warning: invalid character syntax; use ?\s
-e:1: syntax error, unexpected '?', expecting ')'
puts(? )
      ^

Thoughts?

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Used the same coding conventions as the rest of the project.
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• All tests(rake spec) are passing.
• The new code doesn't generate RuboCop offenses that are checked by rake internal_investigation.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[deivid-rodriguez]

PR should be green once #4703 lands.

[Drenmi]

I think at some point, all Parser diagnostics were simply wrapped in cops. I'm okay with removing this, since it's unclear what it's actually checking for (and checking for that can't be automatically tested it seems.)

[bbatsov]

@jonas054 Any thoughts?

[deivid-rodriguez]

Just found an exact duplicate of this, which was closed: https://github.com/bbatsov/rubocop/pull/4086.

[bbatsov]

I recall I closed it mostly because of @rrosenblum's comment. Perhaps there's a real problem, but someone else will have to look into this as I don't have the time to do so right now.

[jonas054]

I think @dorian was right in his comment saying that it's not possible to reach the cop. The errors it checks for are caught by parser (and thus become Lint/Syntax offenses):

ruby -e 'File.write("test.rb", "p(?\t)")'; rubocop -D --only InvalidCharacterLiteral test.rb
Inspecting 1 file
E

Offenses:

test.rb:1:3: W: Lint/Syntax: invalid character syntax; use ?\t
(Using Ruby 2.1 parser; configure using TargetRubyVersion parameter, under AllCops)
p(?	)
  ^^
test.rb:1:3: E: Lint/Syntax: unexpected token tEH
(Using Ruby 2.1 parser; configure using TargetRubyVersion parameter, under AllCops)
p(?	)
  ^

1 file inspected, 2 offenses detected

I recommend we merge this PR.

[deivid-rodriguez]

Yeah, looks like the cop is dead code after all. Codeclimate partially confirms that?¿ https://codeclimate.com/github/bbatsov/rubocop/coverage/59bf68f6de6baf0001000455.

[rrosenblum]

I vaguely remember testing the issue that was mentioned. I don't remember all the details of the issue. Given the new information that we have, I agree that we can remove this cop.

[bbatsov]

I guess the message here should be simply "because it was never being actually triggered" (or something like this).

[bbatsov]

Same here.

[deivid-rodriguez]

@bbatsov Updated!