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mofeiZ
254dc4d9f3
(Found when compiling Meta React code)
Let variable declarations and reassignments are currently rewritten to
`StoreLocal <varName>` instructions, which each translates to a new
`const varName` declaration in codegen.
```js
// Example input
function useHook() {
const getX = () => x;
let x = CONSTANT1;
if (cond) {
x += CONSTANT2;
}
return <Stringify getX={getX} />
}
// Compiled output, prior to this PR
import { c as _c } from "react/compiler-runtime";
function useHook() {
const $ = _c(1);
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
const getX = () => x;
let x = CONSTANT1;
if (cond) {
let x = x + CONSTANT2;
x;
}
t0 = <Stringify getX={getX} />;
$[0] = t0;
} else {
t0 = $[0];
}
return t0;
}
```
This also manifests as a babel internal error when replacing the
original function declaration with the compiler output. The below
compilation output fails with `Duplicate declaration "x" (This is an
error on an internal node. Probably an internal error.)`.
```js
// example input
let x = CONSTANT1;
if (cond) {
x += CONSTANT2;
x = CONSTANT3;
}
// current output
let x = CONSTANT1;
if (playheadDragState) {
let x = x + CONSTANT2
x;
let x = CONSTANT3;
}
```
babel-plugin-react-compiler
React Compiler is a compiler that optimizes React applications, ensuring that only the minimal parts of components and hooks will re-render when state changes. The compiler also validates that components and hooks follow the Rules of React.
This package contains the React Compiler Babel plugin use in projects that make use of Babel. You can find instructions for using this plugin here: https://react.dev/learn/react-compiler