[Fix rubocop#7977] Add Layout/RedundantLineBreak cop

Support method calls and assignments.

Disable the cop by default, but enable it for RuboCop sources.

.rubocop.yml

@@ -47,6 +47,9 @@ Layout/EndOfLine:
 Layout/ClassStructure:
   Enabled: true
 
+Layout/RedundantLineBreak:
+  Enabled: true
+
 Layout/TrailingWhitespace:
   AllowInHeredoc: false
 

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#7977](https://github.com/rubocop/rubocop/issues/7977): Add `Layout/RedundantLineBreak` cop. ([@jonas054][])
+
 ## 1.12.1 (2021-04-04)
 
 ### Bug fixes

config/default.yml

@@ -1101,6 +1101,13 @@ Layout/ParameterAlignment:
   # But it can be overridden by setting this parameter
   IndentationWidth: ~
 
+Layout/RedundantLineBreak:
+  Description: >-
+                 Do not break up an expression into multiple lines when it fits
+                 on a single line.
+  Enabled: false
+  VersionAdded: '<<next>>'
+
 Layout/RescueEnsureAlignment:
   Description: 'Align rescues and ensures correctly.'
   Enabled: true

lib/rubocop.rb

@@ -221,6 +221,7 @@
 require_relative 'rubocop/cop/layout/multiline_method_definition_brace_layout'
 require_relative 'rubocop/cop/layout/multiline_operation_indentation'
 require_relative 'rubocop/cop/layout/parameter_alignment'
+require_relative 'rubocop/cop/layout/redundant_line_break'
 require_relative 'rubocop/cop/layout/rescue_ensure_alignment'
 require_relative 'rubocop/cop/layout/space_after_colon'
 require_relative 'rubocop/cop/layout/space_after_comma'

lib/rubocop/cop/layout/redundant_line_break.rb

@@ -0,0 +1,95 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Layout
+      # This cop checks whether certain expressions, e.g. method calls, that could fit
+      # completely on a single line, are broken up into multiple lines unnecessarily.
+      #
+      # @example
+      #   # bad
+      #   foo(
+      #     a,
+      #     b
+      #   )
+      #
+      #   # good
+      #   foo(a, b)
+      class RedundantLineBreak < Cop
+        include CheckAssignment
+
+        MSG = 'Redundant line break detected.'
+
+        def on_send(node) # rubocop:todo Metrics/CyclomaticComplexity
+          # Include "the whole expression".
+          node = node.parent while convertible_block?(node) ||
+                                   node.parent.is_a?(RuboCop::AST::BinaryOperatorNode) ||
+                                   node.parent&.send_type?
+
+          return unless offense?(node) && !part_of_ignored_node?(node)
+
+          add_offense(node)
+          ignore_node(node)
+        end
+
+        def check_assignment(node, _rhs)
+          return unless offense?(node)
+
+          add_offense(node)
+          ignore_node(node)
+        end
+
+        def autocorrect(node)
+          ->(corrector) { corrector.replace(node.source_range, to_single_line(node.source).strip) }
+        end
+
+        private
+
+        def offense?(node)
+          !single_line?(node) && !too_long?(node) && suitable_as_single_line?(node)
+        end
+
+        def suitable_as_single_line?(node)
+          !comment_within?(node) &&
+            node.each_descendant(:if, :case, :kwbegin, :def).none? &&
+            node.each_descendant(:dstr, :str).none?(&:heredoc?) &&
+            node.each_descendant(:begin).none? { |b| b.first_line != b.last_line }
+        end
+
+        def convertible_block?(node)
+          return false unless node.parent&.block_type?
+
+          send_node = node.parent&.send_node
+          send_node.parenthesized? || !send_node.arguments?
+        end
+
+        def comment_within?(node)
+          processed_source.comments.map(&:loc).map(&:line).any? do |comment_line_number|
+            comment_line_number >= node.first_line && comment_line_number <= node.last_line
+          end
+        end
+
+        def single_line?(node)
+          node.first_line == node.last_line
+        end
+
+        def too_long?(node)
+          lines = processed_source.lines[(node.first_line - 1)...node.last_line]
+          to_single_line(lines.join("\n")).length > max_line_length
+        end
+
+        def to_single_line(source)
+          source
+            .gsub(/" *\\\n\s*'/, %q(" + ')) # Double quote, backslash, and then single quote
+            .gsub(/' *\\\n\s*"/, %q(' + ")) # Single quote, backslash, and then double quote
+            .gsub(/(["']) *\\\n\s*\1/, '')  # Double or single quote, backslash, then same quote
+            .gsub(/\s*\\?\n\s*/, ' ')       # Any other line break, with or without backslash
+        end
+
+        def max_line_length
+          config.for_cop('Layout/LineLength')['Max']
+        end
+      end
+    end
+  end
+end