vendor/pkg-config-0.3.31/README.md

# pkg-config-rs

[![Build Status](https://github.com/rust-lang/pkg-config-rs/actions/workflows/ci.yml/badge.svg)](https://github.com/rust-lang/pkg-config-rs/actions)
[![Rust](https://img.shields.io/badge/rust-1.31%2B-blue.svg?maxAge=3600)](https://github.com/rust-lang/pkg-config-rs/)

[Documentation](https://docs.rs/pkg-config)

A simple library meant to be used as a build dependency with Cargo packages in
order to use the system `pkg-config` tool (if available) to determine where a
library is located.

You can use this crate directly to probe for specific libraries, or use
[system-deps](https://github.com/gdesmott/system-deps) to declare all your
`pkg-config` dependencies in `Cargo.toml`.

This library requires Rust 1.31+.

# Example

Find the system library named `foo`, with minimum version 1.2.3:

```rust
extern crate pkg_config;

fn main() {
    pkg_config::Config::new().atleast_version("1.2.3").probe("foo").unwrap();
}
```

Find the system library named `foo`, with no version requirement (not
recommended):

```rust
extern crate pkg_config;

fn main() {
    pkg_config::probe_library("foo").unwrap();
}
```

# External configuration via target-scoped environment variables

In cross-compilation context, it is useful to manage separately `PKG_CONFIG_PATH`
and a few other variables for the `host` and the `target` platform.

The supported variables are: `PKG_CONFIG_PATH`, `PKG_CONFIG_LIBDIR`, and
`PKG_CONFIG_SYSROOT_DIR`.

Each of these variables can also be supplied with certain prefixes and suffixes, in the following prioritized order:

1. `<var>_<target>` - for example, `PKG_CONFIG_PATH_x86_64-unknown-linux-gnu`
2. `<var>_<target_with_underscores>` - for example, `PKG_CONFIG_PATH_x86_64_unknown_linux_gnu`
3. `<build-kind>_<var>` - for example, `HOST_PKG_CONFIG_PATH` or `TARGET_PKG_CONFIG_PATH`
4. `<var>` - a plain `PKG_CONFIG_PATH`

This crate will allow `pkg-config` to be used in cross-compilation
if `PKG_CONFIG_SYSROOT_DIR` or `PKG_CONFIG` is set. You can set `PKG_CONFIG_ALLOW_CROSS=1`
to bypass the compatibility check, but please note that enabling use of `pkg-config` in
cross-compilation without appropriate sysroot and search paths set is likely to break builds.

Some Rust sys crates support building vendored libraries from source, which may be a work
around for lack of cross-compilation support in `pkg-config`.

# License

This project is licensed under either of

 * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
   https://www.apache.org/licenses/LICENSE-2.0)
 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
   https://opensource.org/licenses/MIT)

at your option.

### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in pkg-config-rs by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.