rspack_collection_hasher

What it does

Warns when HashMap/HashSet-like collections in Rspack use Rust's default hasher, and when Ustr or Identifier keys do not use identity-hasher-based collections.

Why is this bad?

Rspack is a toolchain workload. The collision resistance of Rust's default hasher is not needed for these internal hot paths, while the extra hashing cost is measurable. Ustr and Rspack's Identifier already store precomputed hashes, so they should use IdentityHasher-based collections instead of generic hashers such as FxHasher.

Known problems

This lint intentionally focuses on the collection families used in the Rspack workspace: HashMap/HashSet, IndexMap/IndexSet, DashMap/DashSet, and LinkedHashMap/LinkedHashSet.

Example

use std::collections::HashMap;

let map = HashMap::<String, usize>::new();

Use instead:

use rspack_util::fx_hash::FxHashMap;

let map = FxHashMap::<String, usize>::default();