[Fix #8193] Avoid false positive in Style/RedundantRegexpCharacterClass

CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Bug fixes
 
 * [#8195](https://github.com/rubocop-hq/rubocop/issues/8195): Fix an error for `Style/RedundantFetchBlock` when using `#fetch` with empty block. ([@koic][])
+* [#8193](https://github.com/rubocop-hq/rubocop/issues/8193): Fix a false positive for `Style/RedundantRegexpCharacterClass` when using `[\b]`. ([@owst][])
 
 ## 0.86.0 (2020-06-22)
 

lib/rubocop/cop/style/redundant_regexp_character_class.rb

@@ -34,7 +34,7 @@ class RedundantRegexpCharacterClass < Cop
             \[                # Literal [
             (?!\#\{)          # Not (the start of) an interpolation
             (?:               # Either...
-             \\. |            # Any escaped character
+             \\[^b] |         # Any escaped character except b (which would change behaviour)
              [^.*+?{}()|$] |  # or one that doesn't require escaping outside the character class
              \\[upP]\{[^}]+\} # or a unicode code-point or property
             )

spec/rubocop/cop/style/redundant_regexp_character_class_spec.rb

@@ -121,6 +121,14 @@
     end
   end
 
+  context 'with a character class containing an escaped-b' do
+    # See https://github.com/rubocop-hq/rubocop/issues/8193 for details - in short \b != [\b] - the
+    # former matches a word boundary, the latter a backspace character.
+    it 'does not register an offense' do
+      expect_no_offenses('foo = /[\b]/')
+    end
+  end
+
   context 'with a character class containing a character requiring escape outside' do
     # Not implemented for now, since we would have to escape on auto-correct, and the cop message
     # would need to be dynamic to not be misleading.