[Fix #11150] Catch redundant hyphen escape within character class

changelog/fix_improve_redundant_regex_escape_catching.md

@@ -0,0 +1 @@
+* [#11150](https://github.com/rubocop/rubocop/issues/11150): Improve `Style/RedundantRegexpEscape` to catch unnecessarily escaped hyphens within a character class. ([@si-lens][])

lib/rubocop/cop/style/redundant_regexp_escape.rb

@@ -44,7 +44,7 @@ class RedundantRegexpEscape < Base
 
         def on_regexp(node)
           each_escape(node) do |char, index, within_character_class|
-            next if allowed_escape?(node, char, within_character_class)
+            next if allowed_escape?(node, char, index, within_character_class)
 
             location = escape_range_at_index(node, index)
 
@@ -56,7 +56,7 @@ def on_regexp(node)
 
         private
 
-        def allowed_escape?(node, char, within_character_class)
+        def allowed_escape?(node, char, index, within_character_class)
           # Strictly speaking a few single-letter metachars are currently
           # unnecessary to "escape", e.g. i, E, F, but enumerating them is
           # rather difficult, and their behavior could change over time with
@@ -65,12 +65,21 @@ def allowed_escape?(node, char, within_character_class)
           return true if ALLOWED_ALWAYS_ESCAPES.include?(char) || delimiter?(node, char)
 
           if within_character_class
-            ALLOWED_WITHIN_CHAR_CLASS_METACHAR_ESCAPES.include?(char)
+            ALLOWED_WITHIN_CHAR_CLASS_METACHAR_ESCAPES.include?(char) &&
+              !char_class_begins_or_ends_with_escaped_hyphen?(node, index)
           else
             ALLOWED_OUTSIDE_CHAR_CLASS_METACHAR_ESCAPES.include?(char)
           end
         end
 
+        def char_class_begins_or_ends_with_escaped_hyphen?(node, index)
+          # The hyphen character is allowed to be escaped within a character class
+          # but it's not necessry to escape hyphen if it's the first or last character
+          # within the character class. This method checks if that's the case.
+          # e.g. "[0-9\\-]" or "[\\-0-9]" would return true
+          node.source[index] == '[' || node.source[index + 3] == ']'
+        end
+
         def delimiter?(node, char)
           delimiters = [node.loc.begin.source[-1], node.loc.end.source[0]]
 

spec/rubocop/cop/style/redundant_regexp_escape_spec.rb

@@ -111,6 +111,32 @@
       end
     end
 
+    context "with an escaped '-' character being the last character inside a character class" do
+      it 'registers an offense and corrects' do
+        expect_offense(<<~'RUBY')
+          foo = /[0-9\-]/
+                     ^^ Redundant escape inside regexp literal
+        RUBY
+
+        expect_correction(<<~RUBY)
+          foo = /[0-9-]/
+        RUBY
+      end
+    end
+
+    context "with an escaped '-' character being the first character inside a character class" do
+      it 'registers an offense and corrects' do
+        expect_offense(<<~'RUBY')
+          foo = /[\-0-9]/
+                  ^^ Redundant escape inside regexp literal
+        RUBY
+
+        expect_correction(<<~RUBY)
+          foo = /[-0-9]/
+        RUBY
+      end
+    end
+
     context 'with an escaped character class and following escaped char' do
       it 'does not register an offense' do
         expect_no_offenses('foo = /\[\+/')
@@ -125,7 +151,7 @@
 
     context 'with a nested character class then allowed escape' do
       it 'does not register an offense' do
-        expect_no_offenses('foo = /[a-w&&[^c-g]\-]/')
+        expect_no_offenses('foo = /[a-w&&[^c-g]\-1-9]/')
       end
     end
 
@@ -333,8 +359,15 @@
       end
 
       context "with an escaped '#{char}' inside a character class" do
-        it 'does not register an offense' do
-          expect_no_offenses("foo = /a[\\#{char}]b/")
+        it 'registers an offense and corrects' do
+          expect_offense(<<~RUBY)
+            foo = /a[\\#{char}]b/
+                     ^^ Redundant escape inside regexp literal
+          RUBY
+
+          expect_correction(<<~RUBY)
+            foo = /a[#{char}]b/
+          RUBY
         end
       end
     end