Custom RuboCop cop: convert inline rubocop:disable to standalone disable/enable pairs (rubyfmt-compatible)

no_end_of_line_rubocop_disables.rb

# frozen_string_literal: true

module RuboCop
  module Cop
    module Custom
      # Flags inline `rubocop:disable` and `rubocop:todo` comments on code lines
      # and converts them to standalone disable/enable pairs.
      #
      # rubyfmt places all comments on their own line. For `rubocop:disable`,
      # this silently widens the scope from one line to the rest of the file.
      # See https://github.com/fables-tales/rubyfmt/issues/881 — the rubyfmt
      # maintainers consider this expected behavior. This cop is the
      # codebase-side fix: proactively convert inline disables to explicit
      # disable/enable pairs so rubyfmt can safely reformat them.
      # Approach suggested by @froydnj (rubyfmt collaborator), used at Stripe.
      #
      # `rubocop:todo` gets a standalone comment above but no `enable` — it
      # signals "still needs fixing" rather than a deliberate narrow-scope
      # exemption.
      class NoEndOfLineRubocopDisables < Base
        include RangeHelp
        extend AutoCorrector

        MSG = "Inline `rubocop:%<directive>s` — convert to standalone disable/enable pair."

        DIRECTIVE_PATTERN = /\A#\s*rubocop:(disable|todo)\s+(.+)/

        def on_new_investigation
          processed_source.comments.each do |comment|
            next unless comment.text.include?("rubocop:")

            match = comment.text.match(DIRECTIVE_PATTERN)
            next unless match

            line = processed_source.buffer.source_line(comment.location.line)
            next if line[0...comment.location.column].strip.empty?

            directive_type = match[1]
            add_offense(comment, message: format(MSG, directive: directive_type)) do |corrector|
              autocorrect_comment(corrector, comment, directive_type, match[2], line)
            end
          end
        end

        private

        def autocorrect_comment(corrector, comment, directive_type, directive_body, line)
          indent = line[/\A(\s*)/, 1]
          whole_line = range_by_whole_lines(comment.location.expression, include_final_newline: true)

          code_end_col = line[0...comment.location.column].rstrip.length
          corrector.remove(range_between(whole_line.begin_pos + code_end_col, comment.location.expression.end_pos))

          corrector.insert_before(whole_line, "#{indent}# rubocop:#{directive_type} #{directive_body}\n")

          return unless directive_type == "disable"

          corrector.insert_after(whole_line, "#{indent}# rubocop:enable #{extract_cop_names(directive_body)}\n")
        end

        def extract_cop_names(directive_body)
          directive_body.split("--").first.strip
        end
      end
    end
  end
end

no_end_of_line_rubocop_disables_test.rb

# frozen_string_literal: true

require "minitest/autorun"
require "rubocop"
require_relative "../../../../.rubocop/cop/custom/no_end_of_line_rubocop_disables"

class NoEndOfLineRubocopDisablesTest < Minitest::Test
  CONFIG = RuboCop::ConfigStore.new.for_pwd
  REGISTRY = RuboCop::Cop::Registry.global

  def setup
    @cop = RuboCop::Cop::Custom::NoEndOfLineRubocopDisables.new(CONFIG)
  end

  def offenses_for(source_code)
    investigate(source_code).offenses
  end

  def corrected_source(source_code)
    result = investigate(source_code)
    return source_code if result.offenses.empty?

    rewriter = Parser::Source::TreeRewriter.new(result.offenses.first.location.source_buffer)
    result.offenses.each do |offense|
      rewriter.merge!(offense.corrector) if offense.corrector
    end
    rewriter.process
  end

  # 1. Simple disable → gets converted
  def test_detects_inline_disable
    source = <<~RUBY
      user.update_column(:role, "admin") # rubocop:disable Rails/SkipsModelValidations
    RUBY
    offenses = offenses_for(source)

    assert_equal 1, offenses.size
    assert_includes offenses.first.message, "rubocop:disable"
  end

  def test_autocorrects_inline_disable
    source = <<~RUBY
      user.update_column(:role, "admin") # rubocop:disable Rails/SkipsModelValidations
    RUBY
    expected = <<~RUBY
      # rubocop:disable Rails/SkipsModelValidations
      user.update_column(:role, "admin")
      # rubocop:enable Rails/SkipsModelValidations
    RUBY

    assert_equal expected, corrected_source(source)
  end

  # 2. Simple todo → converted without enable
  def test_detects_inline_todo
    source = <<~RUBY
      x = 1 # rubocop:todo Style/Foo
    RUBY
    offenses = offenses_for(source)

    assert_equal 1, offenses.size
    assert_includes offenses.first.message, "rubocop:todo"
  end

  def test_autocorrects_inline_todo_without_enable
    source = <<~RUBY
      x = 1 # rubocop:todo Style/Foo
    RUBY
    expected = <<~RUBY
      # rubocop:todo Style/Foo
      x = 1
    RUBY

    assert_equal expected, corrected_source(source)
  end

  # 3. Standalone comment → NOT flagged
  def test_ignores_standalone_disable_comment
    source = <<~RUBY
      # rubocop:disable Rails/SkipsModelValidations
      user.update_column(:role, "admin")
      # rubocop:enable Rails/SkipsModelValidations
    RUBY

    assert_empty offenses_for(source)
  end

  def test_ignores_standalone_todo_comment
    source = <<~RUBY
      # rubocop:todo Style/Foo
      x = 1
    RUBY

    assert_empty offenses_for(source)
  end

  # 4. Multiple cops on one disable
  def test_autocorrects_multiple_cops
    source = <<~RUBY
      do_something # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
    RUBY
    expected = <<~RUBY
      # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
      do_something
      # rubocop:enable Metrics/AbcSize, Metrics/MethodLength
    RUBY

    assert_equal expected, corrected_source(source)
  end

  # 5. Disable with reason text
  def test_autocorrects_disable_with_reason
    source = <<~RUBY
      drop_table :claims # rubocop:disable Rails/ReversibleMigration -- one-way data cleanup
    RUBY
    expected = <<~RUBY
      # rubocop:disable Rails/ReversibleMigration -- one-way data cleanup
      drop_table :claims
      # rubocop:enable Rails/ReversibleMigration
    RUBY

    assert_equal expected, corrected_source(source)
  end

  # 6. Indented code in class/method → correct indentation
  def test_autocorrects_indented_code
    source = <<~RUBY
      class Foo
        def bar
          x.save! # rubocop:disable Rails/SaveBang
        end
      end
    RUBY
    expected = <<~RUBY
      class Foo
        def bar
          # rubocop:disable Rails/SaveBang
          x.save!
          # rubocop:enable Rails/SaveBang
        end
      end
    RUBY

    assert_equal expected, corrected_source(source)
  end

  # 7. Regular trailing comment → NOT flagged
  def test_ignores_regular_trailing_comment
    source = <<~RUBY
      x = 1 # some explanation
    RUBY

    assert_empty offenses_for(source)
  end

  def test_ignores_regular_comment_with_rubocop_mention
    source = <<~RUBY
      x = 1 # see rubocop docs
    RUBY

    assert_empty offenses_for(source)
  end

  # Edge: indented standalone comment → NOT flagged
  def test_ignores_indented_standalone_comment
    source = <<~RUBY
      class Foo
        # rubocop:disable Rails/SaveBang
        def bar
          x.save!
        end
        # rubocop:enable Rails/SaveBang
      end
    RUBY

    assert_empty offenses_for(source)
  end

  # Multiple inline disables on separate lines
  def test_autocorrects_multiple_lines
    source = <<~RUBY
      a = 1 # rubocop:disable Style/Foo
      b = 2 # rubocop:disable Style/Bar
    RUBY
    expected = <<~RUBY
      # rubocop:disable Style/Foo
      a = 1
      # rubocop:enable Style/Foo
      # rubocop:disable Style/Bar
      b = 2
      # rubocop:enable Style/Bar
    RUBY

    assert_equal expected, corrected_source(source)
  end

  private

  def investigate(source_code)
    source = RuboCop::ProcessedSource.new(source_code, RUBY_VERSION.to_f)
    source.config = CONFIG
    source.registry = REGISTRY
    commissioner = RuboCop::Cop::Commissioner.new([@cop], raise_error: true)
    commissioner.investigate(source)
  end
end