Add new Style/RedundantAssignment cop

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#7868](https://github.com/rubocop-hq/rubocop/pull/7868): `Cop::Base` is the new recommended base class for cops. ([@marcandre][])
 * [#7458](https://github.com/rubocop-hq/rubocop/issues/7458): Add new `AsciiConstants` option for `Naming/AsciiIdentifiers`. ([@fatkodima][])
+* [#7373](https://github.com/rubocop-hq/rubocop/issues/7373): Add new `Style/RedundantAssignment` cop. ([@fatkodima][])
 * [#8213](https://github.com/rubocop-hq/rubocop/pull/8213): Permit to specify TargetRubyVersion 2.8 (experimental). ([@koic][])
 * [#8164](https://github.com/rubocop-hq/rubocop/pull/8164): Support auto-correction for `Lint/InterpolationCheck`. ([@koic][])
 * [#8223](https://github.com/rubocop-hq/rubocop/pull/8223): Support auto-correction for `Style/IfUnlessModifierOfIfUnless`. ([@koic][])

config/default.yml

@@ -3594,6 +3594,11 @@ Style/RandomWithOffset:
   Enabled: true
   VersionAdded: '0.52'
 
+Style/RedundantAssignment:
+  Description: 'Checks for redundant assignment before returning.'
+  Enabled: 'pending'
+  VersionAdded: '0.87'
+
 Style/RedundantBegin:
   Description: "Don't use begin blocks when they are not needed."
   StyleGuide: '#begin-implicit'

docs/modules/ROOT/pages/cops.adoc

@@ -430,6 +430,7 @@ In the following section you find all available cops:
 * xref:cops_style.adoc#styleproc[Style/Proc]
 * xref:cops_style.adoc#styleraiseargs[Style/RaiseArgs]
 * xref:cops_style.adoc#stylerandomwithoffset[Style/RandomWithOffset]
+* xref:cops_style.adoc#styleredundantassignment[Style/RedundantAssignment]
 * xref:cops_style.adoc#styleredundantbegin[Style/RedundantBegin]
 * xref:cops_style.adoc#styleredundantcapitalw[Style/RedundantCapitalW]
 * xref:cops_style.adoc#styleredundantcondition[Style/RedundantCondition]

docs/modules/ROOT/pages/cops_style.adoc

@@ -6812,6 +6812,56 @@ rand(1...7)
 
 * https://rubystyle.guide#random-numbers
 
+== Style/RedundantAssignment
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| Yes
+| 0.87
+| -
+|===
+
+This cop checks for redundant assignment before returning.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+def test
+  x = foo
+  x
+end
+
+# bad
+def test
+  if x
+    z = foo
+    z
+  elsif y
+    z = bar
+    z
+  end
+end
+
+# good
+def test
+  foo
+end
+
+# good
+def test
+  if x
+    foo
+  elsif y
+    bar
+  end
+end
+----
+
 == Style/RedundantBegin
 
 |===

lib/rubocop.rb

@@ -429,6 +429,7 @@
 require_relative 'rubocop/cop/style/line_end_concatenation'
 require_relative 'rubocop/cop/style/method_call_without_args_parentheses'
 require_relative 'rubocop/cop/style/method_call_with_args_parentheses'
+require_relative 'rubocop/cop/style/redundant_assignment'
 require_relative 'rubocop/cop/style/redundant_fetch_block'
 require_relative 'rubocop/cop/style/method_call_with_args_parentheses/omit_parentheses'
 require_relative 'rubocop/cop/style/method_call_with_args_parentheses/require_parentheses'

lib/rubocop/cop/style/redundant_assignment.rb

@@ -0,0 +1,117 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # This cop checks for redundant assignment before returning.
+      #
+      # @example
+      #   # bad
+      #   def test
+      #     x = foo
+      #     x
+      #   end
+      #
+      #   # bad
+      #   def test
+      #     if x
+      #       z = foo
+      #       z
+      #     elsif y
+      #       z = bar
+      #       z
+      #     end
+      #   end
+      #
+      #   # good
+      #   def test
+      #     foo
+      #   end
+      #
+      #   # good
+      #   def test
+      #     if x
+      #       foo
+      #     elsif y
+      #       bar
+      #     end
+      #   end
+      #
+      class RedundantAssignment < Cop
+        MSG = 'Redundant assignment before returning detected.'
+
+        def_node_matcher :redundant_assignment?, <<~PATTERN
+          (... $(lvasgn _name _expression) (lvar _name))
+        PATTERN
+
+        def on_def(node)
+          check_branch(node.body)
+        end
+        alias on_defs on_def
+
+        def autocorrect(node)
+          lambda do |corrector|
+            expression = node.children[1]
+            corrector.replace(node, expression.source)
+            corrector.remove(right_sibling_of(node))
+          end
+        end
+
+        private
+
+        def check_branch(node)
+          return unless node
+
+          case node.type
+          when :case   then check_case_node(node)
+          when :if     then check_if_node(node)
+          when :rescue, :resbody
+            check_rescue_node(node)
+          when :ensure then check_ensure_node(node)
+          when :begin, :kwbegin
+            check_begin_node(node)
+          end
+        end
+
+        def check_case_node(node)
+          node.when_branches.each { |when_node| check_branch(when_node.body) }
+          check_branch(node.else_branch)
+        end
+
+        def check_if_node(node)
+          return if node.modifier_form? || node.ternary?
+
+          check_branch(node.if_branch)
+          check_branch(node.else_branch)
+        end
+
+        def check_rescue_node(node)
+          node.child_nodes.each do |child_node|
+            check_branch(child_node)
+          end
+        end
+
+        def check_ensure_node(node)
+          check_branch(node.body)
+        end
+
+        def check_begin_node(node)
+          if (assignment = redundant_assignment?(node))
+            add_offense(assignment)
+          else
+            last_expr = node.children.last
+            check_branch(last_expr)
+          end
+        end
+
+        def right_sibling_of(node)
+          siblings_of(node)[node.sibling_index + 1]
+        end
+
+        def siblings_of(node)
+          node.parent.children
+        end
+      end
+    end
+  end
+end

lib/rubocop/name_similarity.rb

@@ -22,9 +22,7 @@ def find_similar_names(target_name, names)
       names.delete(target_name)
 
       spell_checker = DidYouMean::SpellChecker.new(dictionary: names)
-      similar_names = spell_checker.correct(target_name)
-
-      similar_names
+      spell_checker.correct(target_name)
     end
   end
 end