Add new Style/SoleNestedConditional cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#8451](https://github.com/rubocop-hq/rubocop/issues/8451): Add new `Style/RedundantSelfAssignment` cop. ([@fatkodima][])
+* [#8390](https://github.com/rubocop-hq/rubocop/pull/8390): Add new `Style/SoleNestedConditional` cop. ([@fatkodima][])
 * [#8562](https://github.com/rubocop-hq/rubocop/pull/8562): Add new `Style/KeywordParametersOrder` cop. ([@fatkodima][])
 * [#8381](https://github.com/rubocop-hq/rubocop/pull/8381): Add new `Style/ClassMethodsDefinitions` cop. ([@fatkodima][])
 * [#8474](https://github.com/rubocop-hq/rubocop/pull/8474): Add new `Lint/DuplicateRequire` cop. ([@fatkodima][])

config/default.yml

@@ -4030,6 +4030,14 @@ Style/SlicingWithRange:
   VersionAdded: '0.83'
   Safe: false
 
+Style/SoleNestedConditional:
+  Description: >-
+                  Finds sole nested conditional nodes
+                  which can be merged into outer conditional node.
+  Enabled: pending
+  VersionAdded: '0.89'
+  AllowModifier: false
+
 Style/SpecialGlobalVars:
   Description: 'Avoid Perl-style global variables.'
   StyleGuide: '#no-cryptic-perlisms'

docs/modules/ROOT/pages/cops.adoc

@@ -486,6 +486,7 @@ In the following section you find all available cops:
 * xref:cops_style.adoc#stylesinglelineblockparams[Style/SingleLineBlockParams]
 * xref:cops_style.adoc#stylesinglelinemethods[Style/SingleLineMethods]
 * xref:cops_style.adoc#styleslicingwithrange[Style/SlicingWithRange]
+* xref:cops_style.adoc#stylesolenestedconditional[Style/SoleNestedConditional]
 * xref:cops_style.adoc#stylespecialglobalvars[Style/SpecialGlobalVars]
 * xref:cops_style.adoc#stylestabbylambdaparentheses[Style/StabbyLambdaParentheses]
 * xref:cops_style.adoc#stylestderrputs[Style/StderrPuts]

docs/modules/ROOT/pages/cops_style.adoc

@@ -9077,6 +9077,69 @@ items[1..-1]
 items[1..]
 ----
 
+== Style/SoleNestedConditional
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| No
+| 0.89
+| -
+|===
+
+If the branch of a conditional consists solely of a conditional node,
+its conditions can be combined with the conditions of the outer branch.
+This helps to keep the nesting level from getting too deep.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+if condition_a
+  if condition_b
+    do_something
+  end
+end
+
+# good
+if condition_a && condition_b
+  do_something
+end
+----
+
+==== AllowModifier: false (default)
+
+[source,ruby]
+----
+# bad
+if condition_a
+  do_something if condition_b
+end
+----
+
+==== AllowModifier: true
+
+[source,ruby]
+----
+# good
+if condition_a
+  do_something if condition_b
+end
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| AllowModifier
+| `false`
+| Boolean
+|===
+
 == Style/SpecialGlobalVars
 
 |===

lib/rubocop.rb

@@ -458,6 +458,7 @@
 require_relative 'rubocop/cop/style/redundant_fetch_block'
 require_relative 'rubocop/cop/style/redundant_file_extension_in_require'
 require_relative 'rubocop/cop/style/redundant_self_assignment'
+require_relative 'rubocop/cop/style/sole_nested_conditional'
 require_relative 'rubocop/cop/style/method_call_with_args_parentheses/omit_parentheses'
 require_relative 'rubocop/cop/style/method_call_with_args_parentheses/require_parentheses'
 require_relative 'rubocop/cop/style/method_called_on_do_end_block'

lib/rubocop/cop/correctors/alignment_corrector.rb

@@ -47,8 +47,8 @@ def autocorrect_line(corrector, line_begin_pos, expr, column_delta,
           # string literals
           return if taboo_ranges.any? { |t| within?(range, t) }
 
-          if column_delta.positive?
-            corrector.insert_before(range, ' ' * column_delta) unless range.resize(1).source == "\n"
+          if column_delta.positive? && range.resize(1).source != "\n"
+            corrector.insert_before(range, ' ' * column_delta)
           elsif /\A[ \t]+\z/.match?(range.source)
             remove(range, corrector)
           end

lib/rubocop/cop/layout/first_method_argument_line_break.rb

@@ -35,9 +35,8 @@ def on_send(node)
           #
           # ...then each key/value pair is treated as a method 'argument'
           # when determining where line breaks should appear.
-          if (last_arg = args.last)
-            args.concat(args.pop.children) if last_arg.hash_type? && !last_arg.braces?
-          end
+          last_arg = args.last
+          args.concat(args.pop.children) if last_arg&.hash_type? && !last_arg&.braces?
 
           check_method_line_break(node, args)
         end

lib/rubocop/cop/layout/multiline_method_argument_line_breaks.rb

@@ -36,9 +36,8 @@ def on_send(node)
           #
           # ...then each key/value pair is treated as a method 'argument'
           # when determining where line breaks should appear.
-          if (last_arg = args.last)
-            args = args[0...-1] + last_arg.children if last_arg.hash_type? && !last_arg.braces?
-          end
+          last_arg = args.last
+          args = args[0...-1] + last_arg.children if last_arg&.hash_type? && !last_arg&.braces?
 
           check_line_breaks(node, args)
         end

lib/rubocop/cop/layout/space_around_operators.rb

@@ -176,8 +176,8 @@ def enclose_operator_with_space(corrector, range)
           # If `ForceEqualSignAlignment` is true, `Layout/ExtraSpacing` cop
           # inserts spaces before operator. If `Layout/SpaceAroundOperators` cop
           # inserts a space, it collides and raises the infinite loop error.
-          if force_equal_sign_alignment?
-            corrector.insert_after(range, ' ') unless operator.end_with?(' ')
+          if force_equal_sign_alignment? && !operator.end_with?(' ')
+            corrector.insert_after(range, ' ')
           else
             corrector.replace(range, " #{operator.strip} ")
           end

lib/rubocop/cop/lint/missing_super.rb

@@ -56,8 +56,8 @@ class MissingSuper < Base
         def on_def(node)
           return unless offender?(node)
 
-          if node.method?(:initialize)
-            add_offense(node, message: CONSTRUCTOR_MSG) if inside_class_with_stateful_parent?(node)
+          if node.method?(:initialize) && inside_class_with_stateful_parent?(node)
+            add_offense(node, message: CONSTRUCTOR_MSG)
           elsif callback_method_def?(node)
             add_offense(node, message: CALLBACK_MSG)
           end

lib/rubocop/cop/mixin/check_line_breakable.rb

@@ -130,10 +130,9 @@ def contained_by_breakable_collection_on_same_line?(node)
 
       def contained_by_multiline_collection_that_could_be_broken_up?(node)
         node.each_ancestor.find do |ancestor|
-          if ancestor.hash_type? || ancestor.array_type?
-            if breakable_collection?(ancestor, ancestor.children)
-              return children_could_be_broken_up?(ancestor.children)
-            end
+          if (ancestor.hash_type? || ancestor.array_type?) &&
+             breakable_collection?(ancestor, ancestor.children)
+            return children_could_be_broken_up?(ancestor.children)
           end
 
           next unless ancestor.send_type?
@@ -170,9 +169,8 @@ def process_args(args)
         #
         # ...then each key/value pair is treated as a method 'argument'
         # when determining where line breaks should appear.
-        if (last_arg = args.last)
-          args = args[0...-1] + last_arg.children if last_arg.hash_type? && !last_arg.braces?
-        end
+        last_arg = args.last
+        args = args[0...-1] + last_arg.children if last_arg&.hash_type? && !last_arg&.braces?
         args
       end
 

lib/rubocop/cop/style/hash_syntax.rb

@@ -140,11 +140,12 @@ def word_symbol_pair?(pair)
         def acceptable_19_syntax_symbol?(sym_name)
           sym_name.sub!(/\A:/, '')
 
-          if cop_config['PreferHashRocketsForNonAlnumEndingSymbols']
-            # Prefer { :production? => false } over { production?: false } and
-            # similarly for other non-alnum final characters (except quotes,
-            # to prefer { "x y": 1 } over { :"x y" => 1 }).
-            return false unless /[\p{Alnum}"']\z/.match?(sym_name)
+          if cop_config['PreferHashRocketsForNonAlnumEndingSymbols'] &&
+             # Prefer { :production? => false } over { production?: false } and
+             # similarly for other non-alnum final characters (except quotes,
+             # to prefer { "x y": 1 } over { :"x y" => 1 }).
+             !/[\p{Alnum}"']\z/.match?(sym_name)
+            return false
           end
 
           # Most hash keys can be matched against a simple regex.

lib/rubocop/cop/style/if_unless_modifier.rb

@@ -43,8 +43,8 @@ class IfUnlessModifier < Base
           'Modifier form of `%<keyword>s` makes the line too long.'
 
         def on_if(node)
-          msg = if single_line_as_modifier?(node)
-                  MSG_USE_MODIFIER unless named_capture_in_condition?(node)
+          msg = if single_line_as_modifier?(node) && !named_capture_in_condition?(node)
+                  MSG_USE_MODIFIER
                 elsif too_long_due_to_modifier?(node)
                   MSG_USE_NORMAL
                 end

lib/rubocop/cop/style/redundant_parentheses.rb

@@ -112,9 +112,8 @@ def check_unary(begin_node, node)
 
           node = node.children.first while suspect_unary?(node)
 
-          if node.send_type?
-            return unless method_call_with_redundant_parentheses?(node)
-          end
+          return if node.send_type? &&
+                    !method_call_with_redundant_parentheses?(node)
 
           offense(begin_node, 'an unary operation')
         end

lib/rubocop/cop/style/sole_nested_conditional.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # If the branch of a conditional consists solely of a conditional node,
+      # its conditions can be combined with the conditions of the outer branch.
+      # This helps to keep the nesting level from getting too deep.
+      #
+      # @example
+      #   # bad
+      #   if condition_a
+      #     if condition_b
+      #       do_something
+      #     end
+      #   end
+      #
+      #   # good
+      #   if condition_a && condition_b
+      #     do_something
+      #   end
+      #
+      # @example AllowModifier: false (default)
+      #   # bad
+      #   if condition_a
+      #     do_something if condition_b
+      #   end
+      #
+      # @example AllowModifier: true
+      #   # good
+      #   if condition_a
+      #     do_something if condition_b
+      #   end
+      #
+      class SoleNestedConditional < Base
+        MSG = 'Consider merging nested conditions into '\
+              'outer `%<conditional_type>s` conditions.'
+
+        def on_if(node)
+          return if node.ternary? || node.else? || node.elsif?
+
+          branch = node.if_branch
+          return unless offending_branch?(branch)
+
+          message = format(MSG, conditional_type: node.keyword)
+          add_offense(branch.loc.keyword, message: message)
+        end
+
+        private
+
+        def offending_branch?(branch)
+          return false unless branch
+
+          branch.if_type? &&
+            !branch.else? &&
+            !branch.ternary? &&
+            !(branch.modifier_form? && allow_modifier?)
+        end
+
+        def allow_modifier?
+          cop_config['AllowModifier']
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/style/trailing_underscore_variable.rb

@@ -68,11 +68,9 @@ def find_first_possible_offense(variables)
 
             var, = *variable
             var, = *var
-            if allow_named_underscore_variables
-              break offense unless var == :_
-            else
-              break offense unless var.to_s.start_with?(UNDERSCORE)
-            end
+
+            break offense if (allow_named_underscore_variables && var != :_) ||
+                             !var.to_s.start_with?(UNDERSCORE)
 
             variable
           end

lib/rubocop/cop/style/yoda_condition.rb

@@ -154,15 +154,7 @@ def program_name?(name)
         def interpolation?(node)
           return true if node.dstr_type?
 
-          # TODO: Use `RegexpNode#interpolation?` when the following is released.
-          # https://github.com/rubocop-hq/rubocop-ast/pull/18
-          if node.regexp_type?
-            return true if node.children.any? do |child|
-              child.respond_to?(:begin_type?) && child.begin_type?
-            end
-          end
-
-          false
+          node.regexp_type? && node.interpolation?
         end
       end
     end

lib/rubocop/rspec/expect_offense.rb

@@ -241,10 +241,10 @@ def ==(other)
         def match_annotations?(other)
           annotations.zip(other.annotations) do |(_actual_line, actual_annotation),
                                                  (_expected_line, expected_annotation)|
-            if expected_annotation&.end_with?(ABBREV)
-              if actual_annotation.start_with?(expected_annotation[0...-ABBREV.length])
-                expected_annotation.replace(actual_annotation)
-              end
+            if expected_annotation&.end_with?(ABBREV) &&
+               actual_annotation.start_with?(expected_annotation[0...-ABBREV.length])
+
+              expected_annotation.replace(actual_annotation)
             end
           end