Add Style/RedundantRegexpEscape cop (#7908)

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#6289](https://github.com/rubocop-hq/rubocop/issues/6289): Add new `CheckDefinitionPathHierarchy` option for `Naming/FileName`. ([@jschneid][])
 * [#8069](https://github.com/rubocop-hq/rubocop/issues/8069): New option for `expect_offense` to help format offense templates. ([@marcandre][])
+* [#7908](https://github.com/rubocop-hq/rubocop/pull/7908): Add new `Style/RedundantRegexpEscape` cop. ([@owst][])
 
 ### Bug fixes
 

config/default.yml

@@ -3607,6 +3607,11 @@ Style/RedundantPercentQ:
   Enabled: true
   VersionAdded: '0.76'
 
+Style/RedundantRegexpEscape:
+  Description: 'Checks for redundant escapes in Regexps.'
+  Enabled: pending
+  VersionAdded: '0.85'
+
 Style/RedundantReturn:
   Description: "Don't use return where it's not required."
   StyleGuide: '#no-explicit-return'

docs/modules/ROOT/pages/cops.adoc

@@ -437,6 +437,7 @@ In the following section you find all available cops:
 * xref:cops_style.adoc#styleredundantinterpolation[Style/RedundantInterpolation]
 * xref:cops_style.adoc#styleredundantparentheses[Style/RedundantParentheses]
 * xref:cops_style.adoc#styleredundantpercentq[Style/RedundantPercentQ]
+* xref:cops_style.adoc#styleredundantregexpescape[Style/RedundantRegexpEscape]
 * xref:cops_style.adoc#styleredundantreturn[Style/RedundantReturn]
 * xref:cops_style.adoc#styleredundantself[Style/RedundantSelf]
 * xref:cops_style.adoc#styleredundantsort[Style/RedundantSort]

docs/modules/ROOT/pages/cops_style.adoc

@@ -7116,6 +7116,49 @@ question = '"What did you say?"'
 
 * https://rubystyle.guide#percent-q
 
+== Style/RedundantRegexpEscape
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| Yes
+| 0.85
+| -
+|===
+
+This cop checks for redundant escapes inside Regexp literals.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+%r{foo\/bar}
+
+# good
+%r{foo/bar}
+
+# good
+/foo\/bar/
+
+# good
+%r/foo\/bar/
+
+# bad
+/a\-b/
+
+# good
+/a-b/
+
+# bad
+/[\+\-]\d/
+
+# good
+/[+\-]\d/
+----
+
 == Style/RedundantReturn
 
 |===

lib/rubocop.rb

@@ -475,6 +475,7 @@
 require_relative 'rubocop/cop/style/redundant_interpolation'
 require_relative 'rubocop/cop/style/redundant_parentheses'
 require_relative 'rubocop/cop/style/redundant_percent_q'
+require_relative 'rubocop/cop/style/redundant_regexp_escape'
 require_relative 'rubocop/cop/style/redundant_return'
 require_relative 'rubocop/cop/style/redundant_self'
 require_relative 'rubocop/cop/style/redundant_sort'

lib/rubocop/cop/layout/first_array_element_line_break.rb

@@ -37,7 +37,7 @@ def autocorrect(node)
 
         def assignment_on_same_line?(node)
           source = node.source_range.source_line[0...node.loc.column]
-          source =~ /\s*\=\s*$/
+          source =~ /\s*=\s*$/
         end
       end
     end

lib/rubocop/cop/layout/space_around_keyword.rb

@@ -186,7 +186,7 @@ def space_before_missing?(range)
           pos = range.begin_pos - 1
           return false if pos.negative?
 
-          range.source_buffer.source[pos] !~ /[\s\(\|\{\[;,\*\=]/
+          range.source_buffer.source[pos] !~ /[\s(|{\[;,*=]/
         end
 
         def space_after_missing?(range)
@@ -198,7 +198,7 @@ def space_after_missing?(range)
           return false if accept_namespace_operator?(range) &&
                           namespace_operator?(range, pos)
 
-          char !~ /[\s;,#\\\)\}\]\.]/
+          char !~ /[\s;,#\\)}\].]/
         end
 
         def accepted_opening_delimiter?(range, char)

lib/rubocop/cop/naming/file_name.rb

@@ -119,7 +119,7 @@ def allowed_acronyms
 
         def filename_good?(basename)
           basename = basename.sub(/^\./, '')
-          basename = basename.sub(/\.[^\.]+$/, '')
+          basename = basename.sub(/\.[^.]+$/, '')
           # special handling for Action Pack Variants file names like
           # some_file.xlsx+mobile.axlsx
           basename = basename.sub('+', '_')

lib/rubocop/cop/style/multiline_memoization.rb

@@ -82,7 +82,7 @@ def keyword_begin_str(node, node_buf)
         end
 
         def keyword_end_str(node, node_buf)
-          if /[^\s\)]/.match?(node_buf.source_line(node.loc.end.line))
+          if /[^\s)]/.match?(node_buf.source_line(node.loc.end.line))
             "\n" + (' ' * node.loc.column) + 'end'
           else
             'end'

lib/rubocop/cop/style/redundant_regexp_escape.rb

@@ -0,0 +1,118 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # This cop checks for redundant escapes inside Regexp literals.
+      #
+      # @example
+      #   # bad
+      #   %r{foo\/bar}
+      #
+      #   # good
+      #   %r{foo/bar}
+      #
+      #   # good
+      #   /foo\/bar/
+      #
+      #   # good
+      #   %r/foo\/bar/
+      #
+      #   # bad
+      #   /a\-b/
+      #
+      #   # good
+      #   /a-b/
+      #
+      #   # bad
+      #   /[\+\-]\d/
+      #
+      #   # good
+      #   /[+\-]\d/
+      class RedundantRegexpEscape < Cop
+        include RangeHelp
+
+        MSG_REDUNDANT_ESCAPE = 'Redundant escape inside regexp literal'
+
+        ALLOWED_ALWAYS_ESCAPES = ' []^\\#'.chars.freeze
+        ALLOWED_WITHIN_CHAR_CLASS_METACHAR_ESCAPES = '-'.chars.freeze
+        ALLOWED_OUTSIDE_CHAR_CLASS_METACHAR_ESCAPES = '.*+?{}()|$'.chars.freeze
+
+        def on_regexp(node)
+          each_escape(node) do |char, index, within_character_class|
+            next if allowed_escape?(node, char, within_character_class)
+
+            add_offense(
+              node,
+              location: escape_range_at_index(node, index),
+              message: MSG_REDUNDANT_ESCAPE
+            )
+          end
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            each_escape(node) do |char, index, within_character_class|
+              next if allowed_escape?(node, char, within_character_class)
+
+              corrector.remove_leading(escape_range_at_index(node, index), 1)
+            end
+          end
+        end
+
+        private
+
+        def slash_literal?(node)
+          ['/', '%r/'].include?(node.loc.begin.source)
+        end
+
+        def allowed_escape?(node, char, within_character_class)
+          # Strictly speaking a few single-letter metachars are currently
+          # unneccessary to "escape", e.g. g, i, E, F, but enumerating them is
+          # rather difficult, and their behaviour could change over time with
+          # different versions of Ruby so that e.g. /\g/ != /g/
+          return true if /[[:alnum:]]/.match?(char)
+          return true if ALLOWED_ALWAYS_ESCAPES.include?(char)
+
+          if char == '/'
+            slash_literal?(node)
+          elsif within_character_class
+            ALLOWED_WITHIN_CHAR_CLASS_METACHAR_ESCAPES.include?(char)
+          else
+            ALLOWED_OUTSIDE_CHAR_CLASS_METACHAR_ESCAPES.include?(char)
+          end
+        end
+
+        def each_escape(node)
+          pattern_source(node).each_char.with_index.reduce(
+            [nil, false]
+          ) do |(previous, within_character_class), (current, index)|
+            if previous == '\\'
+              yield [current, index - 1, within_character_class]
+
+              [nil, within_character_class]
+            elsif previous == '[' && current != ':'
+              [current, true]
+            elsif previous != ':' && current == ']'
+              [current, false]
+            else
+              [current, within_character_class]
+            end
+          end
+        end
+
+        def escape_range_at_index(node, index)
+          regexp_begin = node.loc.begin.end_pos
+
+          start = regexp_begin + index
+
+          range_between(start, start + 2)
+        end
+
+        def pattern_source(node)
+          node.children.reject(&:regopt_type?).map(&:source).join
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/style/symbol_array.rb

@@ -106,7 +106,7 @@ def symbol_without_quote?(string)
           # method name
           string =~ /\A[a-zA-Z_]\w*[!?]?\z/ ||
             # instance / class variable
-            string =~ /\A\@\@?[a-zA-Z_]\w*\z/ ||
+            string =~ /\A@@?[a-zA-Z_]\w*\z/ ||
             # global variable
             string =~ /\A\$[1-9]\d*\z/ ||
             string =~ /\A\$[a-zA-Z_]\w*\z/ ||

lib/rubocop/magic_comment.rb

@@ -133,7 +133,7 @@ def tokens
     # @see https://www.gnu.org/software/emacs/manual/html_node/emacs/Specify-Coding.html
     # @see https://git.io/vMCXh Emacs handling in Ruby's parse.y
     class EmacsComment < EditorComment
-      FORMAT    = /\-\*\-(.+)\-\*\-/.freeze
+      FORMAT    = /-\*-(.+)-\*-/.freeze
       SEPARATOR = ';'
       OPERATOR  = ':'
 

spec/project_spec.rb

@@ -150,7 +150,7 @@
       describe 'link to related issue' do
         let(:issues) do
           entries.map do |entry|
-            entry.match(/\[(?<number>[#\d]+)\]\((?<url>[^\)]+)\)/)
+            entry.match(/\[(?<number>[#\d]+)\]\((?<url>[^)]+)\)/)
           end.compact
         end
 
@@ -191,7 +191,7 @@
             entry
               .gsub(/`[^`]+`/, '``')
               .sub(/^\*\s*(?:\[.+?\):\s*)?/, '')
-              .sub(/\s*\([^\)]+\)$/, '')
+              .sub(/\s*\([^)]+\)$/, '')
           end
         end
 
@@ -202,7 +202,7 @@
         end
 
         it 'ends with a punctuation' do
-          expect(bodies).to all(match(/[\.\!]$/))
+          expect(bodies).to all(match(/[.!]$/))
         end
       end
     end

spec/rubocop/cli/cli_options_spec.rb

@@ -1005,8 +1005,8 @@ def full_description_of_cop(cop)
            '  Description: Consistent indentation either with tabs only or spaces only.',
            /^  StyleGuide: ('|")#spaces-indentation('|")$/,
            '  Enabled: true',
-           /^  VersionAdded: '[0-9\.]+'$/,
-           /^  VersionChanged: '[0-9\.]+'$/,
+           /^  VersionAdded: '[0-9.]+'$/,
+           /^  VersionChanged: '[0-9.]+'$/,
            '  IndentationWidth:'].join("\n")
         )
       end