Add Style/RedundantRegexpEscape cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#7895](https://github.com/rubocop-hq/rubocop/pull/7895): Include `.simplecov` file by default. ([@robotdana][])
+* [#7908](https://github.com/rubocop-hq/rubocop/pull/7908): Add unnecessary `/`-escapes offence to `Style/RegexpLiteral`. ([@owst][])
 
 ### Bug fixes
 

lib/rubocop/cop/style/regexp_literal.rb

@@ -3,7 +3,8 @@
 module RuboCop
   module Cop
     module Style
-      # This cop enforces using // or %r around regular expressions.
+      # This cop enforces using // or %r around regular expressions, and
+      # prevents unnecessary /-escapes inside %r literals.
       #
       # @example EnforcedStyle: slashes (default)
       #   # bad
@@ -81,12 +82,23 @@ module Style
       # @example AllowInnerSlashes: true
       #   # good
       #   x =~ /home\//
+      #
+      # @example
+      #   # bad
+      #   r = %r{foo\/bar}
+      #
+      #   # good
+      #   r = %r{foo/bar}
+      #
+      #   # good
+      #   r = %r/foo\/bar/
       class RegexpLiteral < Cop
         include ConfigurableEnforcedStyle
         include RangeHelp
 
         MSG_USE_SLASHES = 'Use `//` around regular expression.'
         MSG_USE_PERCENT_R = 'Use `%r` around regular expression.'
+        MSG_UNNECESSARY_ESCAPE = 'Unnecessary `/`-escape inside `%r` literal'
 
         def on_regexp(node)
           if slash_literal?(node)
@@ -98,8 +110,17 @@ def on_regexp(node)
 
         def autocorrect(node)
           lambda do |corrector|
-            correct_delimiters(node, corrector)
-            correct_inner_slashes(node, corrector)
+            if !slash_literal?(node) && allowed_percent_r_literal?(node)
+              correct_inner_slashes(node, corrector, '\/', '/')
+            else
+              correct_delimiters(node, corrector)
+              correct_inner_slashes(
+                node,
+                corrector,
+                inner_slash_before_delimiter_correction(node),
+                inner_slash_after_delimiter_correction(node)
+              )
+            end
           end
         end
 
@@ -112,9 +133,13 @@ def check_slash_literal(node)
         end
 
         def check_percent_r_literal(node)
-          return if allowed_percent_r_literal?(node)
-
-          add_offense(node, message: MSG_USE_SLASHES)
+          if allowed_percent_r_literal?(node)
+            percent_r_unnecessary_escapes(node).each do |loc|
+              add_offense(node, location: loc, message: MSG_UNNECESSARY_ESCAPE)
+            end
+          else
+            add_offense(node, message: MSG_USE_SLASHES)
+          end
         end
 
         def allowed_slash_literal?(node)
@@ -146,6 +171,12 @@ def contains_slash?(node)
           node_body(node).include?('/')
         end
 
+        def percent_r_unnecessary_escapes(node)
+          return [] if percent_r_slash_delimiters?(node) || allow_inner_slashes?
+
+          inner_slash_ranges(node, '\/')
+        end
+
         def allow_inner_slashes?
           cop_config['AllowInnerSlashes']
         end
@@ -159,6 +190,10 @@ def slash_literal?(node)
           node.loc.begin.source == '/'
         end
 
+        def percent_r_slash_delimiters?(node)
+          node.loc.begin.source == '%r/'
+        end
+
         def preferred_delimiters
           config.for_cop('Style/PercentLiteralDelimiters') \
             ['PreferredDelimiters']['%r'].split(//)
@@ -170,25 +205,24 @@ def correct_delimiters(node, corrector)
           corrector.replace(node.loc.end, replacement.last)
         end
 
-        def correct_inner_slashes(node, corrector)
+        def correct_inner_slashes(node, corrector, existing, replacement)
+          inner_slash_ranges(node, existing).map do |range|
+            corrector.replace(range, replacement)
+          end
+        end
+
+        def inner_slash_ranges(node, slash)
           regexp_begin = node.loc.begin.end_pos
 
-          inner_slash_indices(node).each do |index|
+          inner_slash_indices(node, slash).map do |index|
             start = regexp_begin + index
 
-            corrector.replace(
-              range_between(
-                start,
-                start + inner_slash_before_correction(node).length
-              ),
-              inner_slash_after_correction(node)
-            )
+            range_between(start, start + slash.length)
           end
         end
 
-        def inner_slash_indices(node)
+        def inner_slash_indices(node, pattern)
           text    = node_body(node, include_begin_nodes: true)
-          pattern = inner_slash_before_correction(node)
           index   = -1
           indices = []
 
@@ -199,11 +233,11 @@ def inner_slash_indices(node)
           indices
         end
 
-        def inner_slash_before_correction(node)
+        def inner_slash_before_delimiter_correction(node)
           inner_slash_for(node.loc.begin.source)
         end
 
-        def inner_slash_after_correction(node)
+        def inner_slash_after_delimiter_correction(node)
           inner_slash_for(calculate_replacement(node).first)
         end
 

manual/cops_style.md

@@ -5903,7 +5903,8 @@ Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChan
 --- | --- | --- | --- | ---
 Enabled | Yes | Yes  | 0.9 | 0.30
 
-This cop enforces using // or %r around regular expressions.
+This cop enforces using // or %r around regular expressions, and
+prevents unnecessary /-escapes inside %r literals.
 
 ### Examples
 
@@ -5994,6 +5995,16 @@ x =~ %r{home/}
 # good
 x =~ /home\//
 ```
+```ruby
+# bad
+r = %r{foo\/bar}
+
+# good
+r = %r{foo/bar}
+
+# good
+r = %r/foo\/bar/
+```
 
 ### Configurable attributes
 

spec/rubocop/cop/style/regexp_literal_spec.rb

@@ -263,6 +263,26 @@
         RUBY
       end
 
+      describe 'with unnecessarily-escaped slashes' do
+        it 'registers an offense and corrects' do
+          expect_offense(<<~'RUBY')
+            foo = %r{
+              https?:\/\/
+                     ^^ Unnecessary `/`-escape inside `%r` literal
+                       ^^ Unnecessary `/`-escape inside `%r` literal
+              example\.com
+            }x
+          RUBY
+
+          expect_correction(<<~'RUBY')
+            foo = %r{
+              https?://
+              example\.com
+            }x
+          RUBY
+        end
+      end
+
       describe 'when configured to allow inner slashes' do
         before { cop_config['AllowInnerSlashes'] = true }
 
@@ -378,6 +398,19 @@
       end
     end
 
+    describe 'a single-line %r regex with unnecessarily-escaped slashes' do
+      it 'registers an offense and corrects' do
+        expect_offense(<<~'RUBY')
+          foo = %r{home\/}
+                       ^^ Unnecessary `/`-escape inside `%r` literal
+        RUBY
+
+        expect_correction(<<~RUBY)
+          foo = %r{home/}
+        RUBY
+      end
+    end
+
     describe 'a multi-line %r regex without slashes' do
       it 'is accepted' do
         expect_no_offenses(<<~RUBY)
@@ -399,6 +432,26 @@
         RUBY
       end
     end
+
+    describe 'a multi-line %r regex with unnecessarily-escaped slashes' do
+      it 'registers an offense and corrects' do
+        expect_offense(<<~'RUBY')
+          foo = %r{
+            https?:\/\/
+                   ^^ Unnecessary `/`-escape inside `%r` literal
+                     ^^ Unnecessary `/`-escape inside `%r` literal
+            example\.com
+          }x
+        RUBY
+
+        expect_correction(<<~'RUBY')
+          foo = %r{
+            https?://
+            example\.com
+          }x
+        RUBY
+      end
+    end
   end
 
   context 'when EnforcedStyle is set to mixed' do
@@ -542,5 +595,25 @@
         RUBY
       end
     end
+
+    describe 'a multi-line %r regex with unnecessarily-escaped slashes' do
+      it 'registers an offense and corrects' do
+        expect_offense(<<~'RUBY')
+          foo = %r{
+            https?:\/\/
+                   ^^ Unnecessary `/`-escape inside `%r` literal
+                     ^^ Unnecessary `/`-escape inside `%r` literal
+            example\.com
+          }x
+        RUBY
+
+        expect_correction(<<~'RUBY')
+          foo = %r{
+            https?://
+            example\.com
+          }x
+        RUBY
+      end
+    end
   end
 end