Add NoLet cop

Fixes rubocop#862
mockdeep · Aug 7, 2020 · 242d0e9 · 242d0e9
1 parent 38ef169
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -54,6 +54,7 @@
 * Add `RSpec/RepeatedExampleGroupDescription` cop. ([@lazycoder9][])
 * Add block name and other lines to `RSpec/ScatteredSetup` message. ([@elebow][])
 * Fix `RSpec/RepeatedDescription` to take into account example metadata. ([@lazycoder9][])
+* Add `RSpec/MemoizedHelpersInExampleGroup` cop. ([@mockdeep][])
 
 ## 1.37.1 (2019-12-16)
 
@@ -540,3 +541,4 @@ Compatibility release so users can upgrade RuboCop to 0.51.0. No new features.
 [@harrylewis]: https://github.com/harrylewis
 [@elliterate]: https://github.com/elliterate
 [@mlarraz]: https://github.com/mlarraz
+[@mockdeep]: https://github.com/mockdeep
diff --git a/config/default.yml b/config/default.yml
@@ -347,6 +347,13 @@ RSpec/LetSetup:
   VersionAdded: '1.7'
   StyleGuide: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/LetSetup
 
+RSpec/MemoizedHelpersInExampleGroup:
+  Description: Checks if example groups contain too many `let` and `subject` calls.
+  Enabled: false
+  AllowSubject: false
+  Max: 5
+  StyleGuide: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/MemoizedHelpersInExampleGroup
+
 RSpec/MessageChain:
   Description: Check that chains of messages are not being stubbed.
   Enabled: true

diff --git a/lib/rubocop/cop/rspec/memoized_helpers_in_example_group.rb b/lib/rubocop/cop/rspec/memoized_helpers_in_example_group.rb
@@ -0,0 +1,136 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Checks if example groups contain too many `let` and `subject` calls.
+      #
+      # This cop is configurable using the `Max` option and the `AllowSubject`
+      # which will configure the cop to only register offenses on calls to
+      # `let` and not calls to `subject`.
+      #
+      # @example
+      #   # bad
+      #   describe MyClass do
+      #     let(:foo) { [] }
+      #     let(:bar) { [] }
+      #     let!(:booger) { [] }
+      #     subject { {} }
+      #     subject(:wat) { {} }
+      #     subject!(:boo) { {} }
+      #   end
+      #
+      #   describe MyClass do
+      #     let(:foo) { [] }
+      #     let(:bar) { [] }
+      #
+      #     context 'when stuff' do
+      #       let!(:booger) { [] }
+      #       subject { {} }
+      #       subject(:wat) { {} }
+      #       subject!(:boo) { {} }
+      #     end
+      #   end
+      #
+      #   # good
+      #   describe MyClass do
+      #     let(:foo) { [] }
+      #     let!(:booger) { [] }
+      #     subject { {} }
+      #     subject(:wat) { {} }
+      #     subject!(:boo) { {} }
+      #   end
+      #
+      #   describe MyClass do
+      #     context 'when stuff' do
+      #       let(:foo) { [] }
+      #       let(:bar) { [] }
+      #       let!(:booger) { [] }
+      #     end
+      #
+      #     context 'when other stuff' do
+      #       subject { {} }
+      #       subject(:wat) { {} }
+      #       subject!(:boo) { {} }
+      #     end
+      #   end
+      #
+      # @example with AllowSubject configuration
+      #
+      #   # rubocop.yml
+      #   # RSpec/MemoizedHelpersInExampleGroup:
+      #   #   AllowSubject: true
+      #
+      #   # bad
+      #   describe MyClass do
+      #     let(:foo) { [] }
+      #     let(:bar) { [] }
+      #     let!(:booger) { [] }
+      #     let(:subject) { {} }
+      #     let(:wat) { {} }
+      #     let!(:boo) { {} }
+      #   end
+      #
+      #   # good
+      #   describe MyClass do
+      #     let(:foo) { [] }
+      #     let(:bar) { [] }
+      #     let!(:booger) { [] }
+      #     subject { {} }
+      #     subject(:wat) { {} }
+      #     subject!(:boo) { {} }
+      #   end
+      #
+      # @example with Max configuration
+      #
+      #   # rubocop.yml
+      #   # RSpec/MemoizedHelpersInExampleGroup:
+      #   #   Max: 0
+      #
+      #   # bad
+      #   describe MyClass do
+      #     let(:foo) { [] }
+      #   end
+      #
+      #   # good
+      #   describe MyClass do
+      #     def foo; []; end
+      #   end
+      #
+      class MemoizedHelpersInExampleGroup < Cop
+        MSG = 'Example has too many memoized helpers [%<count>d/%<max>d]'
+
+        def on_block(node)
+          return unless spec_group?(node)
+
+          count = count_helpers(node)
+
+          node.each_ancestor(:block) do |ancestor|
+            count += count_helpers(ancestor)
+          end
+
+          return if count <= max
+
+          add_offense(node, message: format(MSG, count: count, max: max))
+        end
+
+        private
+
+        def count_helpers(node)
+          example_group = RuboCop::RSpec::ExampleGroup.new(node)
+          count = example_group.lets.count
+          count += example_group.subjects.count unless allow_subject?
+          count
+        end
+
+        def max
+          cop_config['Max']
+        end
+
+        def allow_subject?
+          cop_config['AllowSubject']
+        end
+      end
+    end
+  end
+end
diff --git a/lib/rubocop/cop/rspec_cops.rb b/lib/rubocop/cop/rspec_cops.rb
@@ -59,6 +59,7 @@
 require_relative 'rspec/leaky_constant_declaration'
 require_relative 'rspec/let_before_examples'
 require_relative 'rspec/let_setup'
+require_relative 'rspec/memoized_helpers_in_example_group'
 require_relative 'rspec/message_chain'
 require_relative 'rspec/message_expectation'
 require_relative 'rspec/message_spies'

diff --git a/manual/cops.md b/manual/cops.md
@@ -58,6 +58,7 @@
 * [RSpec/LeakyConstantDeclaration](cops_rspec.md#rspecleakyconstantdeclaration)
 * [RSpec/LetBeforeExamples](cops_rspec.md#rspecletbeforeexamples)
 * [RSpec/LetSetup](cops_rspec.md#rspecletsetup)
+* [RSpec/MemoizedHelpersInExampleGroup](cops_rspec.md#rspecmemoizedhelpersinexamplegroup)
 * [RSpec/MessageChain](cops_rspec.md#rspecmessagechain)
 * [RSpec/MessageExpectation](cops_rspec.md#rspecmessageexpectation)
 * [RSpec/MessageSpies](cops_rspec.md#rspecmessagespies)

diff --git a/manual/cops_rspec.md b/manual/cops_rspec.md
@@ -1890,6 +1890,122 @@ end
 
 * [https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/LetSetup](https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/LetSetup)
 
+## RSpec/MemoizedHelpersInExampleGroup
+
+Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+--- | --- | --- | --- | ---
+Disabled | Yes | No | - | -
+
+Checks if example groups contain too many `let` and `subject` calls.
+
+This cop is configurable using the `Max` option and the `AllowSubject`
+which will configure the cop to only register offenses on calls to
+`let` and not calls to `subject`.
+
+### Examples
+
+```ruby
+# bad
+describe MyClass do
+  let(:foo) { [] }
+  let(:bar) { [] }
+  let!(:booger) { [] }
+  subject { {} }
+  subject(:wat) { {} }
+  subject!(:boo) { {} }
+end
+
+describe MyClass do
+  let(:foo) { [] }
+  let(:bar) { [] }
+
+  context 'when stuff' do
+    let!(:booger) { [] }
+    subject { {} }
+    subject(:wat) { {} }
+    subject!(:boo) { {} }
+  end
+end
+
+# good
+describe MyClass do
+  let(:foo) { [] }
+  let!(:booger) { [] }
+  subject { {} }
+  subject(:wat) { {} }
+  subject!(:boo) { {} }
+end
+
+describe MyClass do
+  context 'when stuff' do
+    let(:foo) { [] }
+    let(:bar) { [] }
+    let!(:booger) { [] }
+  end
+
+  context 'when other stuff' do
+    subject { {} }
+    subject(:wat) { {} }
+    subject!(:boo) { {} }
+  end
+end
+```
+#### with AllowSubject configuration
+
+```ruby
+# rubocop.yml
+# RSpec/MemoizedHelpersInExampleGroup:
+#   AllowSubject: true
+
+# bad
+describe MyClass do
+  let(:foo) { [] }
+  let(:bar) { [] }
+  let!(:booger) { [] }
+  let(:subject) { {} }
+  let(:wat) { {} }
+  let!(:boo) { {} }
+end
+
+# good
+describe MyClass do
+  let(:foo) { [] }
+  let(:bar) { [] }
+  let!(:booger) { [] }
+  subject { {} }
+  subject(:wat) { {} }
+  subject!(:boo) { {} }
+end
+```
+#### with Max configuration
+
+```ruby
+# rubocop.yml
+# RSpec/MemoizedHelpersInExampleGroup:
+#   Max: 0
+
+# bad
+describe MyClass do
+  let(:foo) { [] }
+end
+
+# good
+describe MyClass do
+  def foo; []; end
+end
+```
+
+### Configurable attributes
+
+Name | Default value | Configurable values
+--- | --- | ---
+AllowSubject | `false` | Boolean
+Max | `5` | Integer
+
+### References
+
+* [https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/MemoizedHelpersInExampleGroup](https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/MemoizedHelpersInExampleGroup)
+
 ## RSpec/MessageChain
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged