[Compiler Bug]: Unicode characters handled incorrectly

[JCown]

What kind of issue is this?

• React Compiler core (the JS output is incorrect, or your app works incorrectly after optimization)
• babel-plugin-react-compiler (build issue installing or using the Babel plugin)
• eslint-plugin-react-compiler (build issue installing or using the eslint plugin)
• react-compiler-healthcheck (build issue installing or using the healthcheck script)

Link to repro

https://playground.react.dev/#N4Igzg9grgTgxgUxALhAgHgBwjALgAgBMEAzAQygBsCSoA7OXASwjvwFkBPAQU0wAoAlPmAAdNvhgJcsNv3H5F+ADxcAwhAC22OgjoFcGXAF5RIAO4JKcLQnyBeDcDSO2fwB6AHwL8ggNziAvuJBulg4BDZ0YATqWjp6BMb4-JgwEJhgwsbuIl5SMjBsyoRMAG7uwClpYAB0hui4-g6Oyq7FZQEg-kA

Repro steps

When passing a unicode character as a prop, like <MyComponent text="welcome 👋" /> then in RC output code we can see <MyComponent text="welcome \uD83D\uDC4B" /> - unicode character gets replaced by "stringified" UTF-16 representation of it.

Expected result (on the screen)
Welcome 👋

Actual result:
Welcome \uD83D\uDC4B

How often does this bug happen?

Every time

What version of React are you using?

19.1

What version of React Compiler are you using?

19.0.0-beta-ebf51a3-20250411

[josephsavona]

Thanks for reporting! I double-checked and React Compiler is not transforming the string contents: the Babel AST node that we construct has the original unescaped string. However, we have previously seen that Babel will escape strings with unicode if those string appear as direct JSX attribute values. This can thankfully be avoided by using an expression container instead:

<Text text="may get escaped by Babel if this has unicode> />
<Text text={"won't get escaped by Babel"} />

We check for unicode and if present emit the latter form. However, it looks like our unicode check only handles codepoints on the basic plane of unicode, and not "astral" planes (i did not make these terms up, i swear). I'll look at how we can detect astral plane codepoints / surrogate pairs.

[josephsavona]

Fixed in #32915

[jurosh]

Fixed in #32915

Wrong link ? Looks like you meant thisone #33096