Commit 8dd097a9 authored by Sean McGivern's avatar Sean McGivern

Add RuboCop cop for custom error classes

From the Ruby style guide:

    # bad
    class FooError < StandardError
    end

    # okish
    class FooError < StandardError; end

    # good
    FooError = Class.new(StandardError)

This cop does that, but only for error classes (classes where the
superclass ends in 'Error'). We have empty controllers and models, which
are perfectly valid empty classes.
parent 6b4d4907
module RuboCop
module Cop
# This cop makes sure that custom error classes, when empty, are declared
# with Class.new.
#
# @example
# # bad
# class FooError < StandardError
# end
#
# # okish
# class FooError < StandardError; end
#
# # good
# FooError = Class.new(StandardError)
class CustomErrorClass < RuboCop::Cop::Cop
MSG = 'Use `Class.new(SuperClass)` to define an empty custom error class.'.freeze
def on_class(node)
_klass, parent, body = node.children
return if body
parent_klass = class_name_from_node(parent)
return unless parent_klass && parent_klass.to_s.end_with?('Error')
add_offense(node, :expression)
end
def autocorrect(node)
klass, parent, _body = node.children
replacement = "#{class_name_from_node(klass)} = Class.new(#{class_name_from_node(parent)})"
lambda do |corrector|
corrector.replace(node.source_range, replacement)
end
end
private
# The nested constant `Foo::Bar::Baz` looks like:
#
# s(:const,
# s(:const,
# s(:const, nil, :Foo), :Bar), :Baz)
#
# So recurse through that to get the name as written in the source.
#
def class_name_from_node(node, suffix = nil)
return unless node&.type == :const
name = node.children[1].to_s
name = "#{name}::#{suffix}" if suffix
if node.children[0]
class_name_from_node(node.children[0], name)
else
name
end
end
end
end
end
require 'spec_helper'
require 'rubocop'
require 'rubocop/rspec/support'
require_relative '../../../rubocop/cop/custom_error_class'
describe RuboCop::Cop::CustomErrorClass do
include CopHelper
subject(:cop) { described_class.new }
context 'when a class has a body' do
it 'does nothing' do
inspect_source(cop, 'class CustomError < StandardError; def foo; end; end')
expect(cop.offenses).to be_empty
end
end
context 'when a class has no explicit superclass' do
it 'does nothing' do
inspect_source(cop, 'class CustomError; end')
expect(cop.offenses).to be_empty
end
end
context 'when a class has a superclass that does not end in Error' do
it 'does nothing' do
inspect_source(cop, 'class CustomError < BasicObject; end')
expect(cop.offenses).to be_empty
end
end
context 'when a class is empty and inherits from a class ending in Error' do
context 'when the class is on a single line' do
let(:source) do
<<-SOURCE
module Foo
class CustomError < Bar::Baz::BaseError; end
end
SOURCE
end
let(:expected) do
<<-EXPECTED
module Foo
CustomError = Class.new(Bar::Baz::BaseError)
end
EXPECTED
end
it 'registers an offense' do
expected_highlights = source.split("\n")[1].strip
inspect_source(cop, source)
aggregate_failures do
expect(cop.offenses.size).to eq(1)
expect(cop.offenses.map(&:line)).to eq([2])
expect(cop.highlights).to contain_exactly(expected_highlights)
end
end
it 'autocorrects to the right version' do
autocorrected = autocorrect_source(cop, source, 'foo/custom_error.rb')
expect(autocorrected).to eq(expected)
end
end
context 'when the class is on multiple lines' do
let(:source) do
<<-SOURCE
module Foo
class CustomError < Bar::Baz::BaseError
end
end
SOURCE
end
let(:expected) do
<<-EXPECTED
module Foo
CustomError = Class.new(Bar::Baz::BaseError)
end
EXPECTED
end
it 'registers an offense' do
expected_highlights = source.split("\n")[1..2].join("\n").strip
inspect_source(cop, source)
aggregate_failures do
expect(cop.offenses.size).to eq(1)
expect(cop.offenses.map(&:line)).to eq([2])
expect(cop.highlights).to contain_exactly(expected_highlights)
end
end
it 'autocorrects to the right version' do
autocorrected = autocorrect_source(cop, source, 'foo/custom_error.rb')
expect(autocorrected).to eq(expected)
end
end
end
end
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