fetch-source

Declare external source dependencies in Cargo.toml and fetch them programmatically.

This crate allows you to define external sources (Git repositories, tar archives) in your Cargo.toml under [package.metadata.fetch-source] and fetch them programmatically. This crate is intended for use in build scripts where Rust bindings are generated from external source(s).

Inspired by CMake's FetchContent module.

Core Features

• Define sources directly in your project metadata.
• Cache fetched sources for efficient sharing between projects.
• Clone git repositories (possibly recursively) by branch, tag, or specific commit (requires git to be installed and available on PATH).

Optional Features

• tar: Download and extract .tar.gz archives. This is an optional feature because it uses the reqwest crate which brings quite a few more dependencies.
• rayon: Fetch sources in parallel with rayon.

Basic Usage

Parse external sources declared in your Cargo.toml like so:

let cargo_toml = r#"
[package.metadata.fetch-source]
my-repo = { git = "https://github.com/user/repo.git", recursive = true }
other-repo = { git = "https://github.com/user/project.git", branch = "the-feature" }
my-data = { tar = "https://example.com/data.tar.gz" }
"#;

for (name, source) in fetch_source::try_parse_toml(cargo_toml)? {
    println!("{name}: {source}");
}

Fetch all sources into a directory:

use std::path::PathBuf;

let cargo_toml = r#"
[package.metadata.fetch-source]
"syn::latest" = { git = "https://github.com/dtolnay/syn.git" }
"syn::1.0.0" = { tar = "https://github.com/dtolnay/syn/archive/refs/tags/1.0.0.tar.gz" }
"#;

let out_dir = PathBuf::from(std::env::temp_dir());
for err in fetch_source::try_parse_toml(cargo_toml)?.into_iter()
    .map(|(_, source)| source.fetch(&out_dir))
    .filter_map(Result::err) {
    eprintln!("{err}");
}

License

Copyright (c) 2025 Adam Tuft

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

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