dillon1000/react

[compiler] repro for dep merging edge case (non-hir)

Found when writing #31037, summary copied from comments:

This is an extreme edge case and not code we'd expect any reasonable developer to write. In most cases e.g. `(a?.b != null ? a.b : DEFAULT)`, we do want to take a dependency on `a?.b`.

I found this trying to come up with edge cases that break the current dependency + CFG merging logic. I think it makes sense to error on the side of correctness. After all, we still take `a` as a dependency if users write `a != null ? a.b : DEFAULT`, and the same fix (understanding the `<hoistable> != null` test expression) works for both. Can be convinced otherwise though!

ghstack-source-id: cc06afda59f7681e228495f5e35a596c20f875f5
Pull Request resolved: https://github.com/facebook/react/pull/31035