Dependencies and features

[dependencies]
geo = { path = "../geo" }
json = { git = "https://github.com/someone/json.git", tag = "v1.2" }

A dependency’s library is reached by its name: geo::distance(a, b). Dependencies are libraries only; their programs and tests never run for you, and their build files only add C compiler arguments (see Build files).

bolt has no registry. Dependencies come from paths and git repositories:

• path: a directory with a bolt.toml.
• git: a repository, at a rev, a branch or a tag (default: its default branch). Git dependencies are cloned into $BOLT_HOME (default $XDG_CACHE_HOME/bolt, else ~/.cache/bolt) and shared between projects.

version = "..." adds a check: the dependency’s [package] version must meet the requirement. 0.2 means ^0.2 (anything compatible), and ~, =, >, >=, <, <=, * and lists like >=1.2, <2 work as in Cargo.

The first build records the exact commit of each git dependency in bolt.lock, next to the workspace’s root manifest; later builds use it, so a build is reproducible until you run bolt update. --locked fails if the lock file would change, --offline never touches the network (bolt fetch downloads everything first), and --frozen is both.

Features are named switches a package offers:

[features]
default = ["color"]
color = []
simd = ["dep:fastmath", "geo/simd"]

[dependencies]
fastmath = { path = "../fastmath", optional = true }

• A feature turns on other features, dep:NAME (an optional dependency) and NAME/FEATURE (a dependency’s feature). NAME?/FEATURE turns the feature on only when something else turns the optional dependency on.
• default is on unless --no-default-features.
• -F simd, --features app/simd, --all-features on the command line.
• A dependency’s features are the union of what everyone asks for.

Code reads its package’s features at compile time:

use std::io;

fn greet() -> void {
    comptime if (@cfg("feature", "color")) {
        std::println("\x1b[33mhello\x1b[0m");
    } else {
        std::println("hello");
    }
}

A branch that’s off isn’t checked, so it can use an optional dependency that isn’t there.

[dev-dependencies] are only for tests, examples and benchmarks.