From: "jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@...>
Date: 2025-11-24T16:54:42+00:00
Subject: [ruby-core:123895] [Ruby Bug#21709] Inconsistent encoding by Regexp.escape

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

Status changed from Open to Feedback

This is not a bug, it is deliberate behavior for ASCII-only strings in `rb_reg_quote` (internal function called by `Regexp.escape`):

```c
    if (ascii_only) {
        rb_enc_associate(tmp, rb_usascii_encoding());
    }
```

`US-ASCII` strings will be automatically converted to UTF-8 if necessary:

```ruby
("foo".encode("US-ASCII") + "\u1234").encoding
# => #<Encoding:UTF-8>
```

Does this behavior cause any problems in your application?

----------------------------------------
Bug #21709: Inconsistent encoding by Regexp.escape
https://bugs.ruby-lang.org/issues/21709#change-115299

* Author: thyresias (Thierry Lambert)
* Status: Feedback
* 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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