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There's a category of bug currently where pruned reactive scopes whose outputs are non-reactive can have their code end up inlining into another scope, moving the location of the instruction. Any value that had a scope assigned has to have its order of evaluation preserved, despite the fact that it got pruned, so naively we could just force every pruned scope to have its declarations promoted to named variables.
However, that ends up assigning names to _tons_ of scope declarations that don't really need to be promoted. For example, a scope with just a hook call ends up with:
```
const x = useFoo();
=>
scope {
$t0 = Call read useFoo$ (...);
}
$t1 = StoreLocal 'x' = read $t0;
```
Where t0 doesn't need to be promoted since it's used immediately to assign to another value which is a non-temporary.
So the idea of this PR is that we can track outputs of pruned scopes which are directly referenced from inside a later scope. This fixes one of the two cases of the above pattern. We'll also likely have to consider values from pruned scopes as always reactive, i'll do that in the next PR.
ghstack-source-id: b37fb9a7cb1430b7c35ec5946269ce5a886a486a
Pull Request resolved: https://github.com/facebook/react/pull/29789
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.
More information about the design and architecture of the compiler are covered in the Design Goals.
More information about developing the compiler itself is covered in the Development Guide.