[Compiler Bug]: Eagerly dereferencing a property from an object that may be undefined #31402
Description
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
Repro steps
export function Component() {
const [crop, setCrop] = React.useState()
const isEmpty = !crop
const onFoo = () => {
if (!isEmpty) {
foo(crop.x)
}
}
return (
<div onClick={onFoo} />
)
}We end up with
function Component() {
const $ = _c(5);
const [crop] = React.useState();
const isEmpty = !crop;
let t0;
if ($[0] !== isEmpty || $[1] !== crop.x) {
t0 = () => {
if (!isEmpty) {
foo(crop.x);
}
};
$[0] = isEmpty;
$[1] = crop.x;
$[2] = t0;
} else {
t0 = $[2];
}
const onFoo = t0;
let t1;
if ($[3] !== onFoo) {
t1 = <div onClick={onFoo} />;
$[3] = onFoo;
$[4] = t1;
} else {
t1 = $[4];
}
return t1;
}The original code isn't accessing crop.x when isEmpty is true, but the generated code does. So it fails with runtime crash. Turning off the compiler fixes it.
How often does this bug happen?
Every time
What version of React are you using?
18
What version of React Compiler are you using?
19.0.0-beta-6fc168f-20241025