Rubocop autocorrection on Atom (simple version but works really good)

init.coffee

# Add this to init.coffee in ~/.atom/
{BufferedProcess} = require 'atom'

rubocopOutput = (data) ->
  if (data.stderr)
    atom.notifications.addError(data.stderr)
    return
  if (data.summary.offense_count == 0)
    atom.notifications.addSuccess('No offenses found')
  for file in data.files
    for offense in file.offenses
      if offense.corrected
        atom.notifications.addSuccess(
          "Fixed: #{offense.location.line}:#{offense.location.column}",
          { detail: "#{offense.message}" }
        )
      else
        atom.notifications.addWarning(
          "#{offense.location.line}:#{offense.location.column}",
          { detail: "#{offense.message}" }
        )

atom.workspace.observeTextEditors (editor) ->
  editor.onDidSave ->
    stdout = (output) =>
      rubocopOutput(JSON.parse(output))
      editor.getBuffer().reload()
    stderr = (output) =>
      rubocopOutput({'stderr': "#{output}"})
    srcFile = editor.getPath()
    command = 'rubocop'
    args = ['-a', '--format', 'json', srcFile]
    new BufferedProcess({ command, args, stdout, stderr })