Cargo Features

[dependencies]
libpng-sys = { version = "1.1.9", default-features = false, features = ["build", "static", "static-libz", "cloudflare-zlib-sys"] }
default = libz-sys

The libz-sys feature is set by default whenever libpng-sys is added without default-features = false somewhere in the dependency tree.

build = static
static build?
static-libz

Enables static of libz-sys

libz-sys:

Enable this feature if you want to have a statically linked libz

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.

libz-sys default static-libz?
cloudflare-zlib-sys implicit feature

Enables cloudflare-zlib-sys

cloudflare-zlib-sys:

Cloudflare fork of zlib with performance improvements