[Fix #7549] Add Style/ArgumentsForwarding cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#8895](https://github.com/rubocop-hq/rubocop/pull/8895): Add new `Lint/EmptyBlock` cop. ([@fatkodima][])
+* [#7549](https://github.com/rubocop-hq/rubocop/issues/7549): Add new `Style/ArgumentsForwarding` cop. ([@koic][])
 
 ## 1.0.0 (2020-10-21)
 

config/default.yml

@@ -2484,6 +2484,13 @@ Style/AndOr:
     - always
     - conditionals
 
+Style/ArgumentsForwarding:
+  Description: 'Use arguments forwarding.'
+  StyleGuide: '#arguments-forwarding'
+  Enabled: pending
+  AllowOnlyRestArgument: true
+  VersionAdded: '1.1'
+
 Style/ArrayCoercion:
   Description: >-
                   Use Array() instead of explicit Array check or [*var], when dealing

docs/modules/ROOT/pages/cops.adoc

@@ -337,6 +337,7 @@ In the following section you find all available cops:
 * xref:cops_style.adoc#styleaccessorgrouping[Style/AccessorGrouping]
 * xref:cops_style.adoc#stylealias[Style/Alias]
 * xref:cops_style.adoc#styleandor[Style/AndOr]
+* xref:cops_style.adoc#styleargumentsforwarding[Style/ArgumentsForwarding]
 * xref:cops_style.adoc#stylearraycoercion[Style/ArrayCoercion]
 * xref:cops_style.adoc#stylearrayjoin[Style/ArrayJoin]
 * xref:cops_style.adoc#styleasciicomments[Style/AsciiComments]

docs/modules/ROOT/pages/cops_style.adoc

@@ -293,6 +293,81 @@ end
 
 * https://rubystyle.guide#no-and-or-or
 
+== Style/ArgumentsForwarding
+
+NOTE: Required Ruby version: 2.7
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| Yes
+| 1.1
+| -
+|===
+
+In Ruby 2.7, arguments forwarding has been added.
+
+This cop identifies places where `do_something(*args, &block)`
+can be replaced by `do_something(...)`.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+def foo(*args, &block)
+  bar(*args, &block)
+end
+
+# bad
+def foo(*args, **kwargs, &block)
+  bar(*args, **kwargs, &block)
+end
+
+# good
+def foo(...)
+  bar(...)
+end
+----
+
+==== AllowOnlyRestArgument: true (default)
+
+[source,ruby]
+----
+# good
+def foo(*args)
+  bar(*args)
+end
+----
+
+==== AllowOnlyRestArgument: false
+
+[source,ruby]
+----
+# bad
+# The following code can replace the arguments with `...`,
+# but it will change the behavior. Because `...` forwards block also.
+def foo(*args)
+  bar(*args)
+end
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| AllowOnlyRestArgument
+| `true`
+| Boolean
+|===
+
+=== References
+
+* https://rubystyle.guide#arguments-forwarding
+
 == Style/ArrayCoercion
 
 |===

lib/rubocop.rb

@@ -385,6 +385,7 @@
 require_relative 'rubocop/cop/style/accessor_grouping'
 require_relative 'rubocop/cop/style/alias'
 require_relative 'rubocop/cop/style/and_or'
+require_relative 'rubocop/cop/style/arguments_forwarding'
 require_relative 'rubocop/cop/style/array_coercion'
 require_relative 'rubocop/cop/style/array_join'
 require_relative 'rubocop/cop/style/ascii_comments'

lib/rubocop/cop/style/arguments_forwarding.rb

@@ -0,0 +1,142 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # In Ruby 2.7, arguments forwarding has been added.
+      #
+      # This cop identifies places where `do_something(*args, &block)`
+      # can be replaced by `do_something(...)`.
+      #
+      # @example
+      #   # bad
+      #   def foo(*args, &block)
+      #     bar(*args, &block)
+      #   end
+      #
+      #   # bad
+      #   def foo(*args, **kwargs, &block)
+      #     bar(*args, **kwargs, &block)
+      #   end
+      #
+      #   # good
+      #   def foo(...)
+      #     bar(...)
+      #   end
+      #
+      # @example AllowOnlyRestArgument: true (default)
+      #   # good
+      #   def foo(*args)
+      #     bar(*args)
+      #   end
+      #
+      # @example AllowOnlyRestArgument: false
+      #   # bad
+      #   # The following code can replace the arguments with `...`,
+      #   # but it will change the behavior. Because `...` forwards block also.
+      #   def foo(*args)
+      #     bar(*args)
+      #   end
+      #
+      class ArgumentsForwarding < Base
+        include RangeHelp
+        extend AutoCorrector
+        extend TargetRubyVersion
+
+        minimum_target_ruby_version 2.7
+
+        MSG = 'Use arguments forwarding.'
+
+        def_node_matcher :use_rest_arguments?, <<~PATTERN
+          (args (restarg $_) $...)
+        PATTERN
+
+        def_node_matcher :only_rest_arguments?, <<~PATTERN
+          (send _ _ (splat (lvar %1)))
+        PATTERN
+
+        def_node_matcher :forwarding_method_arguments?, <<~PATTERN
+          {
+            (send _ _
+              (splat (lvar %1))
+              (block-pass (lvar %2)))
+            (send _ _
+              (splat (lvar %1))
+              (hash (kwsplat (lvar %3)))
+              (block-pass (lvar %2)))
+          }
+        PATTERN
+
+        def on_def(node)
+          return unless node.body
+          return unless (rest_args_name, args = use_rest_arguments?(node.arguments))
+
+          node.each_descendant(:send) do |send_node|
+            kwargs_name, block_name = extract_argument_names_from(args)
+
+            next unless forwarding_method?(send_node, rest_args_name, kwargs_name, block_name) &&
+                        all_lvars_as_forwarding_method_arguments?(node, send_node)
+
+            register_offense_to_forwarding_method_arguments(send_node)
+            register_offense_to_method_definition_arguments(node)
+          end
+        end
+        alias on_defs on_def
+
+        private
+
+        def extract_argument_names_from(args)
+          kwargs_name = args.first.source.delete('**') if args.first&.kwrestarg_type?
+          block_arg_name = args.last.source.delete('&') if args.last&.blockarg_type?
+
+          [kwargs_name, block_arg_name].map { |name| name&.to_sym }
+        end
+
+        def forwarding_method?(node, rest_arg, kwargs, block_arg)
+          return only_rest_arguments?(node, rest_arg) unless allow_only_rest_arguments?
+
+          forwarding_method_arguments?(node, rest_arg, block_arg, kwargs)
+        end
+
+        def all_lvars_as_forwarding_method_arguments?(def_node, forwarding_method)
+          lvars = def_node.body.each_descendant(:lvar, :lvasgn)
+
+          begin_pos = forwarding_method.source_range.begin_pos
+          end_pos = forwarding_method.source_range.end_pos
+
+          lvars.all? do |lvar|
+            lvar.source_range.begin_pos.between?(begin_pos, end_pos)
+          end
+        end
+
+        def register_offense_to_forwarding_method_arguments(forwarding_method)
+          add_offense(arguments_range(forwarding_method)) do |corrector|
+            range = range_between(
+              forwarding_method.loc.selector.end_pos, forwarding_method.source_range.end_pos
+            )
+            corrector.replace(range, '(...)')
+          end
+        end
+
+        def register_offense_to_method_definition_arguments(method_definition)
+          add_offense(arguments_range(method_definition)) do |corrector|
+            arguments_range = range_with_surrounding_space(
+              range: method_definition.arguments.source_range, side: :left
+            )
+            corrector.replace(arguments_range, '(...)')
+          end
+        end
+
+        def arguments_range(node)
+          arguments = node.arguments
+
+          range_between(arguments.first.source_range.begin_pos, arguments.last.source_range.end_pos)
+        end
+
+        def allow_only_rest_arguments?
+          cop_config.fetch('AllowOnlyRestArgument', true)
+        end
+      end
+    end
+  end
+end