[Fix #49] Introduce RescueFromExceptionsVariableName cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#123](https://github.com/rubocop-hq/rubocop-rails/pull/123): Add new `Rails/ApplicationController` and `Rails/ApplicationMailer` cops. ([@eugeneius][])
+* [#139](https://github.com/rubocop-hq/rubocop-rails/pull/139): Add new `Rails/RescueFromExceptionsVariableName` cop. ([@anthony-robin][])
 
 ### Bug fixes
 

config/default.yml

@@ -386,6 +386,12 @@ Rails/RequestReferer:
     - referer
     - referrer
 
+Rails/RescueFromExceptionsVariableName:
+  Description: 'Use consistent rescued exceptions variables naming.'
+  Enabled: true
+  VersionAdded: '2.4'
+  PreferredName: e
+
 Rails/ReversibleMigration:
   Description: 'Checks whether the change method of the migration file is reversible.'
   StyleGuide: 'https://rails.rubystyle.guide#reversible-migration'

lib/rubocop/cop/rails/rescue_from_exceptions_variable_name.rb

@@ -0,0 +1,98 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # This cop makes sure that rescued exceptions variables are named as
+      # expected.
+      #
+      # The `PreferredName` config option takes a `String`. It represents
+      # the required name of the variable. Its default is `e` that is read
+      # from `Naming/RescuedExceptionsVariableName` cop in the main Rubocop
+      # repository.
+      #
+      # @example PreferredName: e (default)
+      #   # bad
+      #   rescue_from MyException do |exception|
+      #     # do something
+      #   end
+      #
+      #   # good
+      #   rescue_from MyException do |e|
+      #     # do something
+      #   end
+      #
+      #   # good
+      #   rescue_from MyException do |_e|
+      #     # do something
+      #   end
+      #
+      # @example PreferredName: exception
+      #   # bad
+      #   rescue_from MyException do |e|
+      #     # do something
+      #   end
+      #
+      #   # good
+      #   rescue_from MyException do |exception|
+      #     # do something
+      #   end
+      #
+      #   # good
+      #   rescue_from MyException do |_exception|
+      #     # do something
+      #   end
+      #
+      class RescueFromExceptionsVariableName < Cop
+        include ConfigurableEnforcedStyle
+
+        MSG = 'Use `%<preferred>s` instead of `%<bad>s`.'
+
+        def on_block(node)
+          name = variable_name(node)
+          return unless name
+          return if preferred_name(name).to_sym == name
+
+          add_offense(node, location: offense_range(node))
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            offending_name = variable_name(node)
+            preferred_name = preferred_name(offending_name)
+            corrector.replace(offense_range(node), "|#{preferred_name}|")
+          end
+        end
+
+        private
+
+        def offense_range(resbody)
+          variable = resbody.node_parts[1]
+          variable.loc.expression
+        end
+
+        def preferred_name(variable_name)
+          preferred_name = cop_config.fetch('PreferredName', 'e')
+          if variable_name.to_s.start_with?('_')
+            "_#{preferred_name}"
+          else
+            preferred_name
+          end
+        end
+
+        def variable_name(node)
+          asgn_node = node.node_parts[1]
+          return unless asgn_node
+
+          asgn_node.children.last&.source&.to_sym
+        end
+
+        def message(node)
+          offending_name = variable_name(node)
+          preferred_name = preferred_name(offending_name)
+          format(MSG, preferred: preferred_name, bad: offending_name)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -48,6 +48,7 @@
 require_relative 'rails/refute_methods'
 require_relative 'rails/relative_date_constant'
 require_relative 'rails/request_referer'
+require_relative 'rails/rescue_from_exceptions_variable_name'
 require_relative 'rails/reversible_migration'
 require_relative 'rails/safe_navigation'
 require_relative 'rails/save_bang'

manual/cops.md

@@ -47,6 +47,7 @@
 * [Rails/RefuteMethods](cops_rails.md#railsrefutemethods)
 * [Rails/RelativeDateConstant](cops_rails.md#railsrelativedateconstant)
 * [Rails/RequestReferer](cops_rails.md#railsrequestreferer)
+* [Rails/RescueFromExceptionsVariableName](cops_rails.md#railsrescuefromexceptionsvariablename)
 * [Rails/ReversibleMigration](cops_rails.md#railsreversiblemigration)
 * [Rails/SafeNavigation](cops_rails.md#railssafenavigation)
 * [Rails/SaveBang](cops_rails.md#railssavebang)

manual/cops_rails.md

@@ -1913,6 +1913,65 @@ Name | Default value | Configurable values
 --- | --- | ---
 EnforcedStyle | `referer` | `referer`, `referrer`
 
+## Rails/RescueFromExceptionsVariableName
+
+Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+--- | --- | --- | --- | ---
+Enabled | Yes | Yes  | 2.4 | -
+
+This cop makes sure that rescued exceptions variables are named as
+expected.
+
+The `PreferredName` config option takes a `String`. It represents
+the required name of the variable. Its default is `e` that is read
+from `Naming/RescuedExceptionsVariableName` cop in the main Rubocop
+repository.
+
+### Examples
+
+#### PreferredName: e (default)
+
+```ruby
+# bad
+rescue_from MyException do |exception|
+  # do something
+end
+
+# good
+rescue_from MyException do |e|
+  # do something
+end
+
+# good
+rescue_from MyException do |_e|
+  # do something
+end
+```
+#### PreferredName: exception
+
+```ruby
+# bad
+rescue_from MyException do |e|
+  # do something
+end
+
+# good
+rescue_from MyException do |exception|
+  # do something
+end
+
+# good
+rescue_from MyException do |_exception|
+  # do something
+end
+```
+
+### Configurable attributes
+
+Name | Default value | Configurable values
+--- | --- | ---
+PreferredName | `e` | String
+
 ## Rails/ReversibleMigration
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged

spec/rubocop/cop/rails/rescue_from_exceptions_variable_name_spec.rb

@@ -0,0 +1,166 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::RescueFromExceptionsVariableName, :config do
+  subject(:cop) { described_class.new(config) }
+
+  it 'does not register an offense without variable' do
+    expect_no_offenses(<<~RUBY)
+      rescue_from MyException do
+        # do something
+      end
+    RUBY
+  end
+
+  context 'with default config' do
+    context 'with default variable' do
+      it 'does not register an offense with a single rescued exception' do
+        expect_no_offenses(<<~RUBY)
+          rescue_from MyException do |e|
+            # do something
+          end
+        RUBY
+      end
+
+      it 'does not register an offense with multiple rescued exceptions' do
+        expect_no_offenses(<<~RUBY)
+          rescue_from MyException, MyOtherException do |e|
+            # do something
+          end
+        RUBY
+      end
+
+      it 'does not register an offense with underscored prefix variable' do
+        expect_no_offenses(<<~RUBY)
+          rescue_from MyException do |_e|
+            # do something
+          end
+        RUBY
+      end
+
+      it 'does not register an offense using splat operator' do
+        expect_no_offenses(<<~RUBY)
+          rescue_from *handled do |e|
+            # do something
+          end
+        RUBY
+      end
+    end
+
+    context 'when using another variable' do
+      it 'registers an offense with a single rescued exception' do
+        expect_offense(<<~RUBY)
+          rescue_from MyException do |exception|
+                                     ^^^^^^^^^^^ Use `e` instead of `exception`.
+            # do something
+          end
+        RUBY
+
+        expect_correction(<<~RUBY)
+          rescue_from MyException do |e|
+            # do something
+          end
+        RUBY
+      end
+
+      it 'registers an offense with multiple rescued exceptions' do
+        expect_offense(<<~RUBY)
+          rescue_from MyException, MyOtherException do |exception|
+                                                       ^^^^^^^^^^^ Use `e` instead of `exception`.
+            # do something
+          end
+        RUBY
+
+        expect_correction(<<~RUBY)
+          rescue_from MyException, MyOtherException do |e|
+            # do something
+          end
+        RUBY
+      end
+
+      it 'registers an offense with underscored prefix variable' do
+        expect_offense(<<~RUBY)
+          rescue_from MyException do |_exception|
+                                     ^^^^^^^^^^^^ Use `_e` instead of `_exception`.
+            # do something
+          end
+        RUBY
+
+        expect_correction(<<~RUBY)
+          rescue_from MyException do |_e|
+            # do something
+          end
+        RUBY
+      end
+
+      it 'registers an offense using splat operator' do
+        expect_offense(<<~RUBY)
+          rescue_from *handled do |exception|
+                                  ^^^^^^^^^^^ Use `e` instead of `exception`.
+            # do something
+          end
+        RUBY
+
+        expect_correction(<<~RUBY)
+          rescue_from *handled do |e|
+            # do something
+          end
+        RUBY
+      end
+    end
+  end
+
+  context 'with the `PreferredName` setup' do
+    let(:cop_config) do
+      {
+        'PreferredName' => 'exception'
+      }
+    end
+
+    it 'does not register an offense when using the preferred name' do
+      expect_no_offenses(<<~RUBY)
+        rescue_from MyException do |exception|
+          # do something
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when using the preferred name with' \
+       'multiple rescued exceptions' do
+      expect_no_offenses(<<~RUBY)
+        rescue_from MyException, MyOtherException do |exception|
+          # do something
+        end
+      RUBY
+    end
+
+    it 'registers an offense when using another name' do
+      expect_offense(<<~RUBY)
+        rescue_from MyException do |e|
+                                   ^^^ Use `exception` instead of `e`.
+          # do something
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        rescue_from MyException do |exception|
+          # do something
+        end
+      RUBY
+    end
+
+    it 'registers an offense with underscored prefix variable' do
+      expect_offense(<<~RUBY)
+        rescue_from MyException do |_e|
+                                   ^^^^ Use `_exception` instead of `_e`.
+          # do something
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        rescue_from MyException do |_exception|
+          # do something
+        end
+      RUBY
+    end
+  end
+end