From: "kddnewton (Kevin Newton) via ruby-core" <ruby-core@...>
Date: 2026-11-09T23:18:01+00:00
Subject: [ruby-core:127391] [Ruby Bug#22519] Incompatibility between parse.y and Prism in the encoding of interpolated strings

Issue #22519 has been updated by kddnewton (Kevin Newton).


https://github.com/ruby/ruby/pull/19815

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Bug #22519: Incompatibility between parse.y and Prism in the encoding of interpolated strings
https://bugs.ruby-lang.org/issues/22519#change-119835

* Author: mame (Yusuke Endoh)
* Status: Open
* Assignee: prism
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
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There seems to be an incompatibility between parse.y and Prism in the encoding of interpolated strings.

```ruby
# in a script file
x = 1
p "#{x}#{x}".encoding  # parse.y: #<Encoding:UTF-8>  prism: #<Encoding:US-ASCII>

a = "abc".force_encoding("US-ASCII")
b = "".encode("UTF-16LE")
s = "#{a}#{b}"
p s.encoding           # parse.y: #<Encoding:UTF-8>  prism: #<Encoding:UTF-16LE>
p s                    # parse.y: "abc"              prism: "\u6261\x63"
```

@naruse says the behavior of parse.y is correct. This is probably a bug in the Prism compiler, but I have not looked into it in detail.

With `-e`, the result of parse.y seems to depend on the locale encoding (the `LANG` environment variable). I have not looked into the details of this either.



-- 
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