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Rollup merge of #131973 - jalil-salame:rustdoc-types-document-feature, r=aDotInTheVoid

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fix(rustdoc-json-types): document rustc-hash feature

The `rustc-hash` feature is publicly exposed by the `rustdoc-types`. It is already documented in that crate's README and Cargo.toml, but we might as well add some information to the crate docs themselves c:

Follow up to:
- #131936
- [rust-lang/rustdoc-types#42][1]

[1]: https://github.com/rust-lang/rustdoc-types/pull/42

r? `@aDotInTheVoid`
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Matthias Krüger 2024-10-20 21:04:14 +02:00 • committed by GitHub
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src/rustdoc-json-types/lib.rs
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@ -2,6 +2,18 @@
//!
//! These types are the public API exposed through the `--output-format json` flag. The [`Crate`]
//! struct is the root of the JSON blob and all other items are contained within.
//!
//! We expose a `rustc-hash` feature that is disabled by default. This feature switches the
//! [`std::collections::HashMap`] for [`rustc_hash::FxHashMap`] to improve the performance of said
//! `HashMap` in specific situations.
//!
//! `cargo-semver-checks` for example, saw a [-3% improvement][1] when benchmarking using the
//! `aws_sdk_ec2` JSON output (~500MB of JSON). As always, we recommend measuring the impact before
//! turning this feature on, as [`FxHashMap`][2] only concerns itself with hash speed, and may
//! increase the number of collisions.
//!
//! [1]: https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/rustc-hash.20and.20performance.20of.20rustdoc-types/near/474855731
//! [2]: https://crates.io/crates/rustc-hash
#[cfg(not(feature = "rustc-hash"))]
use std::collections::HashMap;