From: "jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@...>
Date: 2025-11-24T21:50:49+00:00
Subject: [ruby-core:123899] [Ruby Bug#21709] Inconsistent encoding by Regexp.escape

Issue #21709 has been updated by jeremyevans0 (Jeremy Evans).


thyresias (Thierry Lambert) wrote in #note-4:
> Ok for the workaround, but don't you think all this is inconsistent?
> For me, it's a bug, not a feature. ^_^

I agree this represents a bug, which is why I changed the status back to Open. However, I think the bug is in the literal Regexp support, not in `Regexp.escape`.

In general, US-ASCII strings are implicitly convertible to UTF-8 strings, so having `Regexp.escape` return a US-ASCII string for data that is solely US-ASCII is reasonable. This implicit use of US-ASCII happens in other cases:

```
# Literal Symbol
$ ruby -e "p :a.encoding"
#<Encoding:US-ASCII>

# Array#join
$ ruby -e "p [].join.encoding"
#<Encoding:US-ASCII>

# Literal Regexp
$ ruby -e "p //.encoding"
#<Encoding:US-ASCII>
```


----------------------------------------
Bug #21709: Inconsistent encoding by Regexp.escape
https://bugs.ruby-lang.org/issues/21709#change-115303

* Author: thyresias (Thierry Lambert)
* Status: Open
* ruby -v: ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x64-mingw-ucrt]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
```ruby
%w(foo �tre).each do |s|
  puts "string: #{s.inspect} -> #{s.encoding}"
  puts "escaped: #{Regexp.escape(s).inspect} -> #{Regexp.escape(s).encoding}"
end
```
Output:
```
string: "foo" -> UTF-8
escaped: "foo" -> US-ASCII
string: "�tre" -> UTF-8
escaped: "�tre" -> UTF-8
```
The result should always match the encoding of the argument.



-- 
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