autocorrecting Style/RedundantStringEscape changes program behavior if there are two redundant escapes

[be-ragheb]

When Style/RedundantStringEscape sees a string like this

"\#\{foo}"

it identifies both \# and \{ as redundant string escapes, and if asked to autocorrect, will unescape both, changing the meaning of the program.

---

Expected behavior

Because Style/RedundantStringEscape promises safe autocorrection, I would expect that it would change the offending string to either"#\{foo}" (removing first slash) or "\#{foo}" (removing second slash).

Actual behavior

It actually removes both, resulting in #{foo}. This causes the program to interpolate the value of foo.

Steps to reproduce the problem

Assuming RuboCop is installed, this script will demonstrate the problem:

#!/bin/bash -x

echo 'puts "\#\{foo}"' > demo.rb
ruby demo.rb
rubocop --debug --autocorrect --only Style/RedundantStringEscape demo.rb
ruby demo.rb

Here is the output:

+ echo 'puts "\#\{foo}"'
+ ruby demo.rb
#{foo}
+ rubocop --debug --autocorrect --only Style/RedundantStringEscape demo.rb
For /Users/benragheb/Projects/rubocop-bug: Default configuration from /Users/benragheb/.rvm/gems/ruby-2.6.10/gems/rubocop-1.41.0/config/default.yml
Use parallel by default.
Skipping parallel inspection: only a single file needs inspection
Inspecting 1 file
Scanning /Users/benragheb/Projects/rubocop-bug/demo.rb
Loading cache from /Users/benragheb/.cache/rubocop_cache/5dc345701efc12c82aae8fbc7c2d51bbefd152fa/05097446ed3d3d6bb5a46aa88fe4d53f18d298af/5c20c30dd0b384e0122a1414df3f4ffec395ac2c
C

Offenses:

demo.rb:1:7: C: [Corrected] Style/RedundantStringEscape: Redundant escape of # inside string literal.
puts "\#\{foo}"
      ^^
demo.rb:1:9: C: [Corrected] Style/RedundantStringEscape: Redundant escape of { inside string literal.
puts "\#\{foo}"
        ^^

1 file inspected, 2 offenses detected, 2 offenses corrected
Finished in 0.1450700000859797 seconds
+ ruby demo.rb
demo.rb:1:in `<main>': undefined local variable or method `foo' for main:Object (NameError)

RuboCop version

1.41.0 (using Parser 3.1.3.0, rubocop-ast 1.24.0, running on ruby 2.6.10) [x86_64-darwin21]

[be-ragheb]

@koic Thank you for addressing this so quickly!