React Compiler cuts codegen time, Flight dedupes strings

The headliner this week is the React Compiler's 70% cut in codegen time, achieved by avoiding deep AST clones and quadratic-time codegen [1], plus a reduction in heap allocation through making AbstractValue copyable [2]. These changes directly shorten compile feedback loops for large codebases, a win for teams that hit slow builds on complex components.

Flight dedupes repeated strings in its output, shrinking payloads where the same string recurs across the tree [3]. The effect compounds with the compiler work: less generated code and less redundant serialized content together trim production bundle weight.

The team also hardened its CI pipeline, rebuilding sizebot on a new GitHub Actions token [4], sharding build workers by measured bundle times [5], running setup steps in the background [6][7], and pinning shard weights per run to keep worker assignments stable [8]. The goal is faster, more deterministic CI, which matters if you rely on React's test suite as a canary.

React Native shipped its own stability pass: removing the FileIoHandler cuts a class of security risk [9], and an advisory on Jest's supply chain was scrubbed [10]. Two feature flags were rolled out entirely: enableSchedulerDelegateInvalidation and enableRuntimeSchedulerQueueClearingOnError [11][12]. The latter means error handling now clears the runtime scheduler queue by default, which can change behavior in error paths, so verify your error handling still replays work as expected. A critical shell-quote RCE was patched, so upgrade before your next deploy if you haven't already.