feat: add feature to use rustc-hash (#423)

Cargo.toml

@@ -14,13 +14,16 @@ readme = "./README.md"
 trustfall = "0.7.1"
 rustdoc-types = "0.25.0"
 rayon = { version = "1.10.0", optional = true }
+rustc-hash = { version = "2.0.0", optional = true }
 
 [features]
 default = []
 # Enable rayon for speeding up building `IndexedCrate`, this massively improves
 # performance on big crates, but may impact performance on small crates and
 # definitely increases the memory usage
 rayon = ["dep:rayon"]
+# Use rustc-hash::{FxHashMap, FxHashSet} internally for improved performance
+rustc-hash = ["dep:rustc-hash"]
 
 [[bench]]
 name = "indexed_crate"

src/visibility_tracker.rs

@@ -1,3 +1,6 @@
+#[cfg(feature = "rustc-hash")]
+use rustc_hash::{FxHashMap as HashMap, FxHashSet as HashSet};
+#[cfg(not(feature = "rustc-hash"))]
 use std::collections::{HashMap, HashSet};
 
 use rustdoc_types::{Crate, GenericArgs, Id, Item, ItemEnum, TypeAlias, Visibility};