Add Rails/DurationArithmetic cop

Backed by a proposed guideline rubocop/rails-style-guide#282

CHANGELOG.md

@@ -461,3 +461,4 @@
 [@skryukov]: https://github.com/skryukov
 [@johnsyweb]: https://github.com/johnsyweb
 [@theunraveler]: https://github.com/theunraveler
+[@pirj]: https://github.com/pirj

changelog/new_duration_arithmetic_cop.md

@@ -0,0 +1 @@
+* [#571](https://github.com/rubocop/rubocop-rails/issues/571): Add `Rails/DurationArithmetic` cop. ([@pirj][])

config/default.yml

@@ -245,6 +245,12 @@ Rails/DelegateAllowBlank:
  Enabled: true
  VersionAdded: '0.44'
 
+Rails/DurationArithmetic:
+ Description: 'Do not use duration as arithmetic operand with `Time.current`.'
+ StyleGuide: 'https://rails.rubystyle.guide#duration-arithmetic'
+ Enabled: pending
+ VersionAdded: '2.13'
+
 Rails/DynamicFindBy:
  Description: 'Use `find_by` instead of dynamic `find_by_*`.'
  StyleGuide: 'https://rails.rubystyle.guide#find_by'

docs/modules/ROOT/pages/cops.adoc

@@ -39,6 +39,7 @@ based on the https://rails.rubystyle.guide/[Rails Style Guide].
 * xref:cops_rails.adoc#railsdefaultscope[Rails/DefaultScope]
 * xref:cops_rails.adoc#railsdelegate[Rails/Delegate]
 * xref:cops_rails.adoc#railsdelegateallowblank[Rails/DelegateAllowBlank]
+* xref:cops_rails.adoc#railsdurationarithmetic[Rails/DurationArithmetic]
 * xref:cops_rails.adoc#railsdynamicfindby[Rails/DynamicFindBy]
 * xref:cops_rails.adoc#railseagerevaluationlogmessage[Rails/EagerEvaluationLogMessage]
 * xref:cops_rails.adoc#railsenumhash[Rails/EnumHash]

docs/modules/ROOT/pages/cops_rails.adoc

@@ -1171,6 +1171,42 @@ delegate :foo, to: :bar, allow_blank: true
 delegate :foo, to: :bar, allow_nil: true
 ----
 
+== Rails/DurationArithmetic
+
+|===
+| Enabled by default | Safe | Supports autocorrection | Version Added | Version Changed
+
+| Pending
+| Yes
+| Yes
+| 2.13
+| -
+|===
+
+This cop checks if Duration as added to or subtracted from Time.current.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+Time.current - 1.minute
+Time.current + 2.days
+
+# fair
+Date.yesterday + 3.days
+created_at - 1.minute
+3.days - 1.hour
+
+# good
+1.minute.ago
+2.days.from_now
+----
+
+=== References
+
+* https://rails.rubystyle.guide#duration-arithmetic
+
 == Rails/DynamicFindBy
 
 |===

lib/rubocop/cop/rails/duration_arithmetic.rb

@@ -0,0 +1,97 @@
+# frozen_string_literal: true
+
+module RuboCop
+ module Cop
+ module Rails
+ # This cop checks if Duration as added to or subtracted from Time.current.
+ #
+ # @example
+ # # bad
+ # Time.current - 1.minute
+ # Time.current + 2.days
+ #
+ # # fair
+ # Date.yesterday + 3.days
+ # created_at - 1.minute
+ # 3.days - 1.hour
+ #
+ # # good
+ # 1.minute.ago
+ # 2.days.from_now
+ class DurationArithmetic < Base
+ extend AutoCorrector
+
+ MSG = 'Do not add or subtract duration.'
+
+ RESTRICT_ON_SEND = %i[+ -].freeze
+
+ DURATIONS = Set[:second, :seconds, :minute, :minutes, :hour, :hours,
+ :day, :days, :week, :weeks, :fortnight, :fortnights]
+
+ # @!method duration_arithmetic_argument?(node)
+ # Match duration subtraction or addition with current time.
+ #
+ # @example source that matches
+ # Time.current - 1.hour
+ #
+ # @example source that matches
+ # ::Time.zone.now + 1.hour
+ #
+ # @param node [RuboCop::AST::Node]
+ # @yield operator and duration
+ def_node_matcher :duration_arithmetic_argument?, <<~PATTERN
+ (send #time_current? ${ :+ :- } $#duration?)
+ PATTERN
+
+ # @!method duration?(node)
+ # Match a literal Duration
+ #
+ # @example source that matches
+ # 1.hour
+ #
+ # @example source that matches
+ # 9.5.weeks
+ #
+ # @param node [RuboCop::AST::Node]
+ # @return [Boolean] true if matches
+ def_node_matcher :duration?, '(send { int float (send nil _) } DURATIONS)'
+
+ # @!method time_current?(node)
+ # Match Time.current
+ #
+ # @example source that matches
+ # Time.current
+ #
+ # @example source that matches
+ # ::Time.zone.now
+ #
+ # @param node [RuboCop::AST::Node]
+ # @return [Boolean] true if matches
+ def_node_matcher :time_current?, <<~PATTERN
+ {
+ (send (const _ :Time) :current)
+ (send (send (const _ :Time) :zone) :now)
+ }
+ PATTERN
+
+ def on_send(node)
+ duration_arithmetic_argument?(node) do |*operation|
+ add_offense(node) do |corrector|
+ corrector.replace(node.source_range, corrected_source(*operation))
+ end
+ end
+ end
+
+ private
+
+ def corrected_source(operator, duration)
+ if operator == :-
+ "#{duration.source}.ago"
+ else
+ "#{duration.source}.from_now"
+ end
+ end
+ end
+ end
+ end
+end

lib/rubocop/cop/rails_cops.rb

@@ -28,6 +28,7 @@
 require_relative 'rails/default_scope'
 require_relative 'rails/delegate'
 require_relative 'rails/delegate_allow_blank'
+require_relative 'rails/duration_arithmetic'
 require_relative 'rails/dynamic_find_by'
 require_relative 'rails/eager_evaluation_log_message'
 require_relative 'rails/enum_hash'

spec/rubocop/cop/rails/duration_arithmetic_spec.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::DurationArithmetic, :config do
+ it 'registers an offense and corrects' do
+ expect_offense(<<~RUBY)
+ Time.zone.now - 1.minute
+ ^^^^^^^^^^^^^^^^^^^^^^^^ Do not add or subtract duration.
+ Time.current + 2.days
+ ^^^^^^^^^^^^^^^^^^^^^ Do not add or subtract duration.
+ ::Time.current + 1.hour
+ ^^^^^^^^^^^^^^^^^^^^^^^ Do not add or subtract duration.
+ RUBY
+
+ expect_correction(<<~RUBY)
+ 1.minute.ago
+ 2.days.from_now
+ 1.hour.from_now
+ RUBY
+ end
+
+ it 'does not register an offense for two duration operands' do
+ expect_no_offenses(<<~RUBY)
+ 3.days - 1.hour
+ 3.days + 1.hour
+ RUBY
+ end
+
+ it 'does not register an offense if the left operand is non current time' do
+ expect_no_offenses(<<~RUBY)
+ 5.hours + Time.current # will raise
+ Date.yesterday + 3.days
+ created_at - 1.minute
+ RUBY
+ end
+end