Simplify and allow to configure rubocop formatter

[jimeh]

This effectively simplifies and enhances how Solargraph interacts with RuboCop in three specific ways. Below is a summary, more details about each change is in the commit messages.

• Removes the need of creating/reading/writing any temporary files on disk when formatting code, by passing it in to rubocop in-memory via its STDIN options.
• The STDIN method means that the real original filepath on disk can be provided to rubocop, allowing it to correctly find any relevant .rubocop.yml config files itself, negating the need for Solargraph to have it's own implementation of rubocop config file finding. So no -c option is needed within the formatter, nor was it needed within the diagnostics implementation as that already used the STDIN method.
• A new formatter option is available within Solargraph's own configuration file, which allows some basic customization of rubocop. This is useful if you want to disable certain cops when formatting from within your editor, but you otherwise want the cops enabled when manually running rubocop.

Update: I'm not sure why it's not displayed here in the PR, but the Travis-CI build has passed: https://travis-ci.org/github/castwide/solargraph/builds/753192754

---

I believe this PR will fix #401, as no temp directory/file is used anymore, and rubocop's config is correctly picked up by rubocop itself without any intervention by Solargraph.

[jimeh]

(Updated to reflect latest configuration options in this PR)

For reference, I personally use the following configuration for Solargraph:

~/.config/solargraph/config.yml

---
exclude:
  - vendor/**/*
  - ".bundle/**/*"
reporters:
  - rubocop
  - require_not_found
  - typecheck
max_files: 5000
formatter:
  rubocop:
    cops: all
    except:
      - Lint/Debugger
      - Lint/UnusedBlockArgument
      - Lint/UnusedMethodArgument
      - Style/EmptyMethod

For a short explanation of why I disable each of those cops, see the Disabled Cops section in the README of my rubocopfmt.el Emacs package.

[castwide]

Thanks, @jimeh. I'm testing the PR locally and everything seems to work.

The one issue is the formatter option. An upcoming feature will allow users to change formatting tools via plugins, with the default configuration being formatter: rubocop. Maybe we could use a rubocop option instead?

[jimeh]

@castwide I'm happy to change the config options. Personally I think having formatter involved somehow might help make it clearer that these options only applies to the rubocop based formatter, and not the linter/diagnostics.

To make things simple, pick from A, B, and C below, or feel free to suggest a different structure that you prefer :)

A:

rubocop:
  cops: all
  extra_args:
    - --except
    - Lint/Debugger,Lint/UnusedBlockArgument,Lint/UnusedMethodArgument,Style/EmptyMethod

B:

formatter:
  rubocop:
    cops: all
    extra_args:
      - --except
      - Lint/Debugger,Lint/UnusedBlockArgument,Lint/UnusedMethodArgument,Style/EmptyMethod

C:

rubocop:
  formatter:
    cops: all
    extra_args:
      - --except
      - Lint/Debugger,Lint/UnusedBlockArgument,Lint/UnusedMethodArgument,Style/EmptyMethod

While we're on the topic of config, I'm planning to add except and only as legit options later today, so I can specify them directly as YAML arrays, rather than through extra_args.

[castwide]

I think either B or C would be best. I slightly prefer B, but the implementation might be a little hairy, since the formatter option would need to be capable of recognizing the formatter name by either a string (formatter = "rubocop") or a hash key (formatter = {"rubocop" => {"cops" => "all"}}).

[jimeh]

@castwide I've gone with option B as it was your preferred variant, and honestly it was my preferred one too.

It did lead to slightly annoying checking logic with the new config_for method, that ensures that the config variable is always as Hash, so things don't break regardless of what might or might not be in the solargraph config file.

I also added the except and only config options I mentioned, so the config now covers all of my own usecases at least.

[castwide]

@jimeh Thanks for making these changes. With 0.40.2 released today, I expect to merge this PR shortly and release it in 0.41.0.

[jimeh]

@castwide let me know if you want me to rebase on top of master or something before you merge :)

[jsmestad]

Waiting patiently for this to drop so I can start using solargraph again 🤞 🎉

[pelletencate]

@jsmestad Anything stopping you from temporarily using @jimeh's branch? Works wonders for me!

# Gemfile

  # TODO: Revert on resolution of castwide/solargraph#403
  # gem "solargraph", "~> 0.40.0"
  gem "solargraph", github: "jimeh/solargraph", branch: "fix-rubocop-formatting"

[jimeh]

I've just rebased my changes here on top of latest changes in master.

[castwide]

Thanks, @jimeh. I'll go ahead and merge this now. I was on the fence about whether to publish this without the upcoming formatter plugin support, but it should be fine either way.