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Swaps the default hashers across the Rust compiler crates for rustc-hash's faster `FxHasher`. ## Why `FxHasher` is a simple, fast, non-cryptographic hasher. std's default (SipHash) is DoS-resistant but heavy — the compiler keys maps/sets almost entirely on small integer IDs (`IdentifierId`, `BlockId`, `ScopeId`, …) where that protection buys nothing. Switching gives: - **Performance** — faster hashing on the hot ID-keyed maps/sets used throughout the passes. - **Slight binary size reduction** — drops the heavy SipHash hasher pulled in by std's `HashMap`/`HashSet`. ## Changes - `std::collections::HashMap`/`HashSet` → `rustc_hash::FxHashMap`/`FxHashSet` - `indexmap` `IndexMap`/`IndexSet` now use `FxBuildHasher`, inlined as `IndexMap<K, V, FxBuildHasher>` (no `FxIndexMap` type aliases) - `rustc-hash = "2"` added to all 12 crate manifests - `rustc_hash`/`indexmap` imports consolidated into single brace imports at the top of each file The change is serde-neutral: `FxHashMap` and `IndexMap<_, _, FxBuildHasher>` serialize to byte-identical JSON, and `IndexMap` keeps insertion order. `cargo check`, `cargo fmt --check`, and `cargo test` all pass with no warnings.
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.