Add new Lint/DuplicateRescueException cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#8322](https://github.com/rubocop-hq/rubocop/pull/8322): Support autocorrect for `Style/CaseEquality` cop. ([@fatkodima][])
+* [#8389](https://github.com/rubocop-hq/rubocop/pull/8389): Add new `Lint/DuplicateRescueException` cop. ([@fatkodima][])
 * [#8376](https://github.com/rubocop-hq/rubocop/pull/8376): Add new `Lint/MissingSuper` cop. ([@fatkodima][])
 * [#8339](https://github.com/rubocop-hq/rubocop/pull/8339): Add `Config#for_badge` as an efficient way to get a cop's config merged with its department's. ([@marcandre][])
 * [#5067](https://github.com/rubocop-hq/rubocop/issues/5067): Add new `Style/StringConcatenation` cop. ([@fatkodima][])

config/default.yml

@@ -1420,6 +1420,11 @@ Lint/DuplicateMethods:
   Enabled: true
   VersionAdded: '0.29'
 
+Lint/DuplicateRescueException:
+  Description: 'Checks that there are no repeated exceptions used in `rescue` expressions.'
+  Enabled: pending
+  VersionAdded: '0.89'
+
 Lint/EachWithObjectArgument:
   Description: 'Check for immutable argument given to each_with_object.'
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -196,6 +196,7 @@ In the following section you find all available cops:
 * xref:cops_lint.adoc#lintduplicateelsifcondition[Lint/DuplicateElsifCondition]
 * xref:cops_lint.adoc#lintduplicatehashkey[Lint/DuplicateHashKey]
 * xref:cops_lint.adoc#lintduplicatemethods[Lint/DuplicateMethods]
+* xref:cops_lint.adoc#lintduplicaterescueexception[Lint/DuplicateRescueException]
 * xref:cops_lint.adoc#linteachwithobjectargument[Lint/EachWithObjectArgument]
 * xref:cops_lint.adoc#lintelselayout[Lint/ElseLayout]
 * xref:cops_lint.adoc#lintemptyensure[Lint/EmptyEnsure]

docs/modules/ROOT/pages/cops_lint.adoc

@@ -739,6 +739,44 @@ end
 alias bar foo
 ----
 
+== Lint/DuplicateRescueException
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| No
+| 0.89
+| -
+|===
+
+This cop checks that there are no repeated exceptions
+used in 'rescue' expressions.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+begin
+  something
+rescue FirstException
+  handle_exception
+rescue FirstException
+  handle_other_exception
+end
+
+# good
+begin
+  something
+rescue FirstException
+  handle_exception
+rescue SecondException
+  handle_other_exception
+end
+----
+
 == Lint/EachWithObjectArgument
 
 |===

lib/rubocop.rb

@@ -253,6 +253,7 @@
 require_relative 'rubocop/cop/lint/duplicate_elsif_condition'
 require_relative 'rubocop/cop/lint/duplicate_hash_key'
 require_relative 'rubocop/cop/lint/duplicate_methods'
+require_relative 'rubocop/cop/lint/duplicate_rescue_exception'
 require_relative 'rubocop/cop/lint/each_with_object_argument'
 require_relative 'rubocop/cop/lint/else_layout'
 require_relative 'rubocop/cop/lint/empty_ensure'

lib/rubocop/cop/lint/duplicate_rescue_exception.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks that there are no repeated exceptions
+      # used in 'rescue' expressions.
+      #
+      # @example
+      #   # bad
+      #   begin
+      #     something
+      #   rescue FirstException
+      #     handle_exception
+      #   rescue FirstException
+      #     handle_other_exception
+      #   end
+      #
+      #   # good
+      #   begin
+      #     something
+      #   rescue FirstException
+      #     handle_exception
+      #   rescue SecondException
+      #     handle_other_exception
+      #   end
+      #
+      class DuplicateRescueException < Base
+        include RescueNode
+
+        MSG = 'Duplicate `rescue` exception detected.'
+
+        def on_rescue(node)
+          return if rescue_modifier?(node)
+
+          _body, *resbodies, _else = *node
+
+          resbodies.each_with_object(Set.new) do |resbody, previous|
+            rescued_exceptions = rescued_exceptions(resbody)
+
+            rescued_exceptions.each do |exception|
+              add_offense(exception) unless previous.add?(exception)
+            end
+          end
+        end
+
+        private
+
+        def rescued_exceptions(resbody)
+          rescue_group, = *resbody
+          if rescue_group
+            rescue_group.values
+          else
+            []
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/duplicate_rescue_exception_spec.rb

@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::DuplicateRescueException do
+  subject(:cop) { described_class.new }
+
+  it 'registers an offense when duplicate exception exists' do
+    expect_offense(<<~RUBY)
+      begin
+        something
+      rescue FirstError
+      rescue SecondError, FirstError
+                          ^^^^^^^^^^ Duplicate `rescue` exception detected.
+      end
+    RUBY
+  end
+
+  it 'registers an offense when duplicate exception splat exists' do
+    expect_offense(<<~RUBY)
+      begin
+        something
+      rescue *ERRORS
+      rescue SecondError, *ERRORS
+                          ^^^^^^^ Duplicate `rescue` exception detected.
+      end
+    RUBY
+  end
+
+  it 'registers an offense when multiple duplicate exceptions exist' do
+    expect_offense(<<~RUBY)
+      begin
+        something
+      rescue FirstError
+      rescue SecondError
+      rescue FirstError
+             ^^^^^^^^^^ Duplicate `rescue` exception detected.
+      rescue SecondError
+             ^^^^^^^^^^^ Duplicate `rescue` exception detected.
+      end
+    RUBY
+  end
+
+  it 'registers an offense when duplicate exception exists within rescues with `else` branch' do
+    expect_offense(<<~RUBY)
+      begin
+        something
+      rescue FirstError
+      rescue SecondError, FirstError
+                          ^^^^^^^^^^ Duplicate `rescue` exception detected.
+      else
+      end
+    RUBY
+  end
+
+  it 'registers an offense when duplicate exception exists within rescues with empty `rescue` branch' do
+    expect_offense(<<~RUBY)
+      begin
+        something
+      rescue FirstError
+      rescue SecondError, FirstError
+                          ^^^^^^^^^^ Duplicate `rescue` exception detected.
+      rescue
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when there are no duplicate exceptions' do
+    expect_no_offenses(<<~RUBY)
+      begin
+        something
+      rescue FirstError
+      rescue SecondError
+      end
+    RUBY
+  end
+end