Cargo Features

hg-git-fast-import has no features set by default.

hg-git-fast-import = { version = "1.4.0", features = ["jemalloc"] }
jemalloc = jemallocator

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

jemallocator jemalloc?