Read and parse the Cargo.toml manifest file of a Rust crate

As part of the Rust Digger project I wanted to read the Cargo.toml file that comes with the project. At first I tried the read_manifest method of the Cargo crate, but I could not figure out how to use it.

Luckily then I encountered the cargo_toml crate that provides a much easier way to get started.

Dependencies

examples/read-cargo-toml/Cargo.toml

[package]
name = "read-cargo-toml"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cargo_toml = "0.19.2"

The code:

examples/read-cargo-toml/src/main.rs

use cargo_toml::{Edition, Manifest};

fn main() {
    for filename in vec![
        "Cargo_only_edition.toml",
        "Cargo_only_version.toml",
        "Cargo_both_edition_and_version.toml",
        "Cargo_neither.toml",
    ] {
        println!("{filename}");

        let manifest = std::fs::read_to_string(filename).unwrap();
        let cargo_toml = Manifest::from_str(&manifest).unwrap();

        //println!("{cargo_toml:?}");
        match cargo_toml.package().rust_version() {
            Some(rust_version) => println!("{rust_version}"),
            None => println!("No rust-version"),
        }

        let edition = cargo_toml.package().edition();
        let year = match edition {
            Edition::E2015 => "2015",
            Edition::E2018 => "2018",
            Edition::E2021 => "2021",
        };
        println!("edition {year}");

        println!("------");
    }

    let filename = "Cargo_invalid_field.toml";

    let manifest = std::fs::read_to_string(filename).unwrap();
    let cargo_toml = Manifest::from_str(&manifest).unwrap();
    println!("{:#?}", cargo_toml);
}

My current interests are the edition and the rust-version fields as I am working on the issue of MSRV (Minimum Supported Rust Version) indication.

Two observations:

• The Edition field will default to 2015.

• IF there are invalid fields they are disregarded.

The various sample input files:

examples/read-cargo-toml/Cargo_only_edition.toml

[package]
name = "read-cargo-toml"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cargo_toml = "0.19.2"

examples/read-cargo-toml/Cargo_only_version.toml

[package]
name = "read-cargo-toml"
version = "0.1.0"
rust-version = "1.77"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cargo_toml = "0.19.2"

examples/read-cargo-toml/Cargo_both_edition_and_version.toml

[package]
name = "read-cargo-toml"
version = "0.1.0"
edition = "2021"
rust-version = "1.77"
invalid-field = "invalid value"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cargo_toml = "0.19.2"

examples/read-cargo-toml/Cargo_neither.toml

[package]
name = "read-cargo-toml"
version = "0.1.0"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cargo_toml = "0.19.2"

examples/read-cargo-toml/Cargo_invalid_field.toml

[package]
name = "read-cargo-toml"
version = "0.1.0"
edition = "2021"
invalid_field = "invalid value"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cargo_toml = "0.19.2"

The output:

Cargo_only_edition.toml
No rust-version
edition 2021
------
Cargo_only_version.toml
1.77
edition 2015
------
Cargo_both_edition_and_version.toml
1.77
edition 2021
------
Cargo_neither.toml
No rust-version
edition 2015
------

Manifest {
    package: Some(
        Package {
            name: "read-cargo-toml",
            edition: Set(
                E2021,
            ),
            rust_version: None,
            version: Set(
                "0.1.0",
            ),
            build: None,
            workspace: None,
            authors: Set(
                [],
            ),
            links: None,
            description: None,
            homepage: None,
            documentation: None,
            readme: Set(
                Flag(
                    true,
                ),
            ),
            keywords: Set(
                [],
            ),
            categories: Set(
                [],
            ),
            exclude: Set(
                [],
            ),
            include: Set(
                [],
            ),
            license: None,
            license_file: None,
            repository: None,
            default_run: None,
            autobins: true,
            autoexamples: true,
            autotests: true,
            autobenches: true,
            publish: Set(
                Flag(
                    true,
                ),
            ),
            resolver: None,
            metadata: None,
        },
    ),
    workspace: None,
    dependencies: {
        "cargo_toml": Simple(
            "0.19.2",
        ),
    },
    dev_dependencies: {},
    build_dependencies: {},
    target: {},
    features: {},
    replace: {},
    patch: {},
    lib: None,
    profile: Profiles {
        release: None,
        dev: None,
        test: None,
        bench: None,
        doc: None,
        custom: {},
    },
    badges: Badges {
        appveyor: None,
        circle_ci: None,
        gitlab: None,
        travis_ci: None,
        codecov: None,
        coveralls: None,
        is_it_maintained_issue_resolution: None,
        is_it_maintained_open_issues: None,
        maintenance: Maintenance {
            status: None,
        },
    },
    bin: [],
    bench: [],
    test: [],
    example: [],
    lints: None,
}