Cargo and Package Management

Cargo.toml

The Cargo.toml file is the manifest of a Rust package, written in the TOML (Tom's Obvious, Minimal Language) format. It declares package metadata, the Rust edition, minimum supported Rust version (rust-version), compilation targets, dependency graphs, feature flags, and build profiles.

Cargo.toml Sections:
  [package]             --> Name, version, edition = "2024", rust-version, license
  [lib] / [[bin]]       --> Explicit target path and crate-type overrides
  [dependencies]        --> Runtime library dependencies
  [dev-dependencies]    --> Test, example, and benchmark-only dependencies
  [build-dependencies]  --> Dependencies available to `build.rs`
  [features]            --> Conditional compilation feature flags
  [profile.*]           --> Optimization, debuginfo, LTO, and panic settings
  [lints]               --> Compiler (`[lints.rust]`) and Clippy (`[lints.clippy]`) rules

Complete Cargo.toml Manifest Reference

[package]
name = "telemetry_agent"
version = "0.3.1"
edition = "2024"
rust-version = "1.85"
authors = ["Platform Team <platform@example.com>"]
description = "Lightweight structured telemetry collector and batch shipper"
license = "MIT OR Apache-2.0"
repository = "https://github.com/example/telemetry_agent"
readme = "README.md"
keywords = ["telemetry", "metrics", "observability"]
categories = ["development-tools::profiling", "network-programming"]

[dependencies]
serde = { version = "1.0", features = ["derive"] }
bytes = "1.9"

[dev-dependencies]
proptest = "1.6"

[features]
default = ["compression"]
compression = []

[lints.rust]
unsafe_code = "forbid"

[lints.clippy]
all = { level = "warn", priority = -1 }
unwrap_used = "warn"

[profile.release]
lto = "thin"
codegen-units = 1
strip = "symbols"

Key [package] Fields

Field Required? Purpose
name Yes Package identifier ([a-zA-Z0-9_-]). Hyphens - in package names are automatically converted to underscores _ in Rust code (use telemetry_agent::...).
version Yes (default "0.1.0") Semantic version string (MAJOR.MINOR.PATCH).
edition Recommended ("2024") Selects the Rust language and Cargo resolver edition ("2015", "2018", "2021", "2024"). Omitting it defaults to "2015".
rust-version Optional Minimum Supported Rust Version (MSRV), e.g., "1.85". In edition = "2024", Cargo's v3 resolver prefers dependency versions compatible with this rust-version.
license / license-file Required for crates.io SPDX 2.1 license expression (such as "MIT OR Apache-2.0").
publish Optional (true) Setting publish = false prevents accidental cargo publish of internal proprietary packages.
default-run Optional Specifies which binary cargo run executes by default when a package has multiple binaries.

Configuring Lints in Cargo.toml ([lints])

Instead of repeating #![warn(...)] attributes at the top of src/lib.rs, src/main.rs, and every binary target, declaring [lints.rust] and [lints.clippy] in Cargo.toml applies those lint levels uniformly across every target in the package.

pub fn parse_metric_id(raw: &str) -> Option<u64> {
    raw.strip_prefix("m_")?.parse().ok()
}

fn main() {
    println!("Metric ID: {:?}", parse_metric_id("m_4096"));
}

Metric ID: Some(4096)