Add new Naming/RescuedExceptionsVariableName cop

Use a consistent naming of the rescued exceptions variable. Prevent
naming rescued `Exception` variable other than the preferred configured
one.

The default naming configuration is "ex".

CHANGELOG.md

@@ -7,6 +7,7 @@
 * [#5184](https://github.com/rubocop-hq/rubocop/issues/5184): Add new multiline element line break cops. ([@maxh][])
 * Add new cop `Rails/ActiveRecordOverride` that checks for overriding Active Record methods instead of using callbacks. ([@elebow][])
 * Add new cop `Rails/RedundantAllowNil` that checks for cases when `allow_blank` makes `allow_nil` unnecessary in model validations. ([@elebow][])
+* Add new `Naming/RescuedExceptionsVariableName` cop. ([@AdrienSldy][])
 
 ### Bug fixes
 
@@ -3730,6 +3731,7 @@
 [@sue445]: https://github.com/sue445
 [@zverok]: https://github.com/zverok
 [@backus]: https://github.com/backus
+[@AdrienSldy]: https://github.com/adriensldy
 [@pat]: https://github.com/pat
 [@sinsoku]: https://github.com/sinsoku
 [@nodo]: https://github.com/nodo

Rakefile

@@ -8,10 +8,10 @@ require 'bundler'
 require 'bundler/gem_tasks'
 begin
   Bundler.setup(:default, :development)
-rescue Bundler::BundlerError => e
-  warn e.message
+rescue Bundler::BundlerError => ex
+  warn ex.message
   warn 'Run `bundle install` to install missing gems'
-  exit e.status_code
+  exit ex.status_code
 end
 require 'rake'
 require 'rubocop/rake_task'

config/default.yml

@@ -1935,6 +1935,12 @@ Naming/PredicateName:
   Exclude:
     - 'spec/**/*'
 
+Naming/RescuedExceptionsVariableName:
+  Description: 'Use consistent rescued exceptions variables naming.'
+  Enabled: true
+  VersionAdded: '0.67'
+  PreferredName: ex
+
 Naming/UncommunicativeBlockParamName:
   Description: >-
                 Checks for block parameter names that contain capital letters,

lib/rubocop.rb

@@ -363,6 +363,7 @@
 require_relative 'rubocop/cop/naming/method_name'
 require_relative 'rubocop/cop/naming/binary_operator_parameter_name'
 require_relative 'rubocop/cop/naming/predicate_name'
+require_relative 'rubocop/cop/naming/rescued_exceptions_variable_name'
 require_relative 'rubocop/cop/naming/uncommunicative_block_param_name'
 require_relative 'rubocop/cop/naming/uncommunicative_method_param_name'
 require_relative 'rubocop/cop/naming/variable_name'

lib/rubocop/cli.rb

@@ -45,21 +45,23 @@ def run(args = ARGV)
       act_on_options
       apply_default_formatter
       execute_runners(paths)
-    rescue ConfigNotFoundError, IncorrectCopNameError, OptionArgumentError => e
-      warn e.message
+    rescue ConfigNotFoundError,
+           IncorrectCopNameError,
+           OptionArgumentError => ex
+      warn ex.message
       STATUS_ERROR
-    rescue RuboCop::Error => e
-      warn Rainbow("Error: #{e.message}").red
+    rescue RuboCop::Error => ex
+      warn Rainbow("Error: #{ex.message}").red
       STATUS_ERROR
     rescue Finished
       STATUS_SUCCESS
-    rescue OptionParser::InvalidOption => e
-      warn e.message
+    rescue OptionParser::InvalidOption => ex
+      warn ex.message
       warn 'For usage information, use --help'
       STATUS_ERROR
-    rescue StandardError, SyntaxError, LoadError => e
-      warn e.message
-      warn e.backtrace
+    rescue StandardError, SyntaxError, LoadError => ex
+      warn ex.message
+      warn ex.backtrace
       STATUS_ERROR
     end
     # rubocop:enable Metrics/MethodLength, Metrics/AbcSize

lib/rubocop/config_loader_resolver.rb

@@ -190,9 +190,9 @@ def transform(config)
     def gem_config_path(gem_name, relative_config_path)
       spec = Gem::Specification.find_by_name(gem_name)
       File.join(spec.gem_dir, relative_config_path)
-    rescue Gem::LoadError => e
+    rescue Gem::LoadError => ex
       raise Gem::LoadError,
-            "Unable to find gem #{gem_name}; is the gem installed? #{e}"
+            "Unable to find gem #{gem_name}; is the gem installed? #{ex}"
     end
   end
 end

lib/rubocop/cop/commissioner.rb

@@ -104,14 +104,14 @@ def invoke_custom_processing(cops_or_forces, processed_source)
       # cops' `#investigate` methods.
       def with_cop_error_handling(cop, node = nil)
         yield
-      rescue StandardError => e
-        raise e if @options[:raise_error]
+      rescue StandardError => ex
+        raise ex if @options[:raise_error]
 
         if node
           line = node.first_line
           column = node.loc.column
         end
-        error = CopError.new(e, line, column)
+        error = CopError.new(ex, line, column)
         @errors[cop] << error
       end
     end

lib/rubocop/cop/naming/rescued_exceptions_variable_name.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Naming
+      # 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`.
+      #
+      # @example PreferredName: e (default)
+      #   # bad
+      #   begin
+      #     # do something
+      #   rescue MyException => exc
+      #     # do something
+      #   end
+      #
+      #   # good
+      #   begin
+      #     # do something
+      #   rescue MyException => e
+      #     # do something
+      #   end
+      #
+      # @example PreferredName: exception
+      #   # bad
+      #   begin
+      #     # do something
+      #   rescue MyException => e
+      #     # do something
+      #   end
+      #
+      #   # good
+      #   begin
+      #     # do something
+      #   rescue MyException => ex
+      #     # do something
+      #   end
+      #
+      class RescuedExceptionsVariableName < Cop
+        MSG = 'Use `%<preferred>s` instead of `%<bad>s`.'.freeze
+
+        def on_resbody(node)
+          exception_type, @exception_name = *node
+          return unless exception_type || @exception_name
+
+          @exception_name ||= exception_type.children.first
+          return if @exception_name.const_type? ||
+                    variable_name == preferred_name
+
+          add_offense(node, location: location)
+        end
+
+        private
+
+        def preferred_name
+          @preferred_name ||= cop_config.fetch('PreferredName', 'e')
+        end
+
+        def variable_name
+          @variable_name ||= location.source
+        end
+
+        def location
+          @location ||= @exception_name.loc.expression
+        end
+
+        def message(_node = nil)
+          format(MSG, preferred: preferred_name, bad: variable_name)
+        end
+      end
+    end
+  end
+end

lib/rubocop/path_util.rb

@@ -41,10 +41,10 @@ def match_path?(pattern, path)
       when Regexp
         begin
           path =~ pattern
-        rescue ArgumentError => e
-          return false if e.message.start_with?('invalid byte sequence')
+        rescue ArgumentError => ex
+          return false if ex.message.start_with?('invalid byte sequence')
 
-          raise e
+          raise exception
         end
       end
     end

lib/rubocop/processed_source.rb

@@ -146,8 +146,8 @@ def parse(source, ruby_version)
 
       begin
         @buffer.source = source
-      rescue EncodingError => error
-        @parser_error = error
+      rescue EncodingError => ex
+        @parser_error = ex
         return
       end
 

lib/rubocop/remote_config.rb

@@ -47,8 +47,8 @@ def request(uri = @uri, limit = 10, &block)
       generate_request(uri) do |request|
         begin
           handle_response(http.request(request), limit, &block)
-        rescue SocketError => err
-          handle_response(err, limit, &block)
+        rescue SocketError => ex
+          handle_response(ex, limit, &block)
         end
       end
     end
@@ -72,8 +72,10 @@ def handle_response(response, limit, &block)
       else
         begin
           response.error!
-        rescue StandardError => e
-          raise e, "#{e.message} while downloading remote config file #{uri}"
+        rescue StandardError => ex
+          message = "#{ex.message} while downloading remote config"\
+            " file #{uri}"
+          raise ex, message
         end
       end
     end

lib/rubocop/result_cache.rb

@@ -100,9 +100,9 @@ def save(offenses)
 
       begin
         FileUtils.mkdir_p(dir)
-      rescue Errno::EACCES => e
+      rescue Errno::EACCES => ex
         warn "Couldn't create cache directory. Continuing without cache."\
-             "\n  #{e.message}"
+             "\n  #{ex.message}"
         return
       end
 

lib/rubocop/runner.rb

@@ -108,8 +108,8 @@ def process_file(file)
       end
       formatter_set.file_finished(file, offenses)
       offenses
-    rescue InfiniteCorrectionLoop => e
-      formatter_set.file_finished(file, e.offenses.compact.sort.freeze)
+    rescue InfiniteCorrectionLoop => ex
+      formatter_set.file_finished(file, ex.offenses.compact.sort.freeze)
       raise
     end
 

lib/rubocop/target_finder.rb

@@ -145,8 +145,13 @@ def ruby_executable?(file)
 
       first_line = File.open(file, &:readline)
       !(first_line =~ /#!.*(#{ruby_interpreters(file).join('|')})/).nil?
-    rescue EOFError, ArgumentError => e
-      warn "Unprocessable file #{file}: #{e.class}, #{e.message}" if debug?
+    rescue EOFError, ArgumentError => ex
+      if debug?
+        warn(
+          "Unprocessable file #{file}: #{ex.class}, #{ex.message}"
+        )
+      end
+
       false
     end
 

manual/cops.md

@@ -298,6 +298,7 @@ In the following section you find all available cops:
 * [Naming/MemoizedInstanceVariableName](cops_naming.md#namingmemoizedinstancevariablename)
 * [Naming/MethodName](cops_naming.md#namingmethodname)
 * [Naming/PredicateName](cops_naming.md#namingpredicatename)
+* [Naming/RescuedExceptionsVariableName](cops_naming.md#namingrescuedexceptionsvariablename)
 * [Naming/UncommunicativeBlockParamName](cops_naming.md#naminguncommunicativeblockparamname)
 * [Naming/UncommunicativeMethodParamName](cops_naming.md#naminguncommunicativemethodparamname)
 * [Naming/VariableName](cops_naming.md#namingvariablename)

manual/cops_naming.md

@@ -191,7 +191,7 @@ Name | Default value | Configurable values
 --- | --- | ---
 Exclude | `[]` | Array
 ExpectMatchingDefinition | `false` | Boolean
-Regex | `<none>` | 
+Regex | `<none>` |
 IgnoreExecutableScripts | `true` | Boolean
 AllowedAcronyms | `CLI`, `DSL`, `ACL`, `API`, `ASCII`, `CPU`, `CSS`, `DNS`, `EOF`, `GUID`, `HTML`, `HTTP`, `HTTPS`, `ID`, `IP`, `JSON`, `LHS`, `QPS`, `RAM`, `RHS`, `RPC`, `SLA`, `SMTP`, `SQL`, `SSH`, `TCP`, `TLS`, `TTL`, `UDP`, `UI`, `UID`, `UUID`, `URI`, `URL`, `UTF8`, `VM`, `XML`, `XMPP`, `XSRF`, `XSS` | Array
 
@@ -477,6 +477,61 @@ Exclude | `spec/**/*` | Array
 
 * [https://github.com/rubocop-hq/ruby-style-guide#bool-methods-qmark](https://github.com/rubocop-hq/ruby-style-guide#bool-methods-qmark)
 
+## Naming/RescuedExceptionsVariableName
+
+Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+--- | --- | --- | --- | ---
+Enabled | Yes | No | 0.67 | -
+
+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`.
+
+### Examples
+
+#### PreferredName: e (default)
+
+```ruby
+# bad
+begin
+  # do something
+rescue MyException => exc
+  # do something
+end
+
+# good
+begin
+  # do something
+rescue MyException => e
+  # do something
+end
+```
+#### PreferredName: exception
+
+```ruby
+# bad
+begin
+  # do something
+rescue MyException => e
+  # do something
+end
+
+# good
+begin
+  # do something
+rescue MyException => ex
+  # do something
+end
+```
+
+### Configurable attributes
+
+Name | Default value | Configurable values
+--- | --- | ---
+PreferredName | `ex` | String
+
 ## Naming/UncommunicativeBlockParamName
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged

spec/rubocop/cli_spec.rb

@@ -1602,9 +1602,9 @@ def method(foo, bar, qux, fred, arg5, f) end #{'#' * 45}
     it 'shows an error if the input file cannot be found' do
       begin
         cli.run(%w[/tmp/not_a_file])
-      rescue SystemExit => e
-        expect(e.status).to eq(1)
-        expect(e.message)
+      rescue SystemExit => ex
+        expect(ex.status).to eq(1)
+        expect(ex.message)
           .to eq 'rubocop: No such file or directory -- /tmp/not_a_file'
       end
     end