specify build dependency of a feature (lemmy.blahaj.zone)

submitted 1 week ago by protogen420@lemmy.blahaj.zone to c/rust@lemmy.ml

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[features]
default = ["runtime_completion_gen", "comptime_completion_gen", "comptime_manpage_gen"]
runtime_completion_gen = ["dep:clap_complete",]
comptime_completion_gen = ["dep:clap_complete"]
comptime_manpage_gen = ["dep:clap_mangen"]

[dependencies]
anyhow = "1.0.0"
clap = { version = "4.0.0", features = ["derive", "help"] }
clap_complete = { version = "4.0.0", optional = true }
ignore = "0.4.25"

[build-dependencies]
clap = { version = "4.0.0", features = ["derive"] }
clap_complete = { version = "4.0.0", optional = true }
clap_mangen = { version = "0.2.31", optional = true }

The features that start with comptime, as their name suggest, happen at comp time in build.rs, they generate shell completions and manpages for my cli utility, thus they depend only at build time to their respective dependencies, but there seems no way to specify this.

Does anyone know if there is a way to specify build deps for a feature?

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[-] BB_C@programming.dev 1 points 1 week ago

I don't understand the problem.

cargo new tt-build
cd tt-build
cargo new --lib opt-dep
echo 'pub const NAME: &str = "opt-dep";' > opt-dep/src/lib.rs

// build.rs
fn main() {
    #[cfg(feature = "opt_dep_b_ft")]
    println!("cargo:warning={}", opt_dep::NAME);
    #[cfg(not(feature = "opt_dep_b_ft"))]
    println!("cargo:warning=none");
}

// src/main.rs
fn main() {
    #[cfg(feature = "opt_dep_r_ft")]
    println!("Hello with {}", opt_dep::NAME);
    #[cfg(not(feature = "opt_dep_r_ft"))]
    println!("Hello with none");
}

# Cargo.toml
[package]
name = "tt-build"
version = "0.1.0"
edition = "2024"

[features]
default = ["opt_dep_b_ft", "opt_dep_r_ft"]
opt_dep_b_ft= ["dep:opt-dep"]
opt_dep_r_ft= ["dep:opt-dep"]

[dependencies]
opt-dep = { path = "./opt-dep", optional = true }

[build-dependencies]
opt-dep = { path = "./opt-dep", optional = true }

% cargo run --no-default-features 2>&1 | rg 'Hello|warn'
warning: tt-build@0.1.0: none
Hello with none

% cargo run  2>&1 | rg 'Hello|warn'
warning: tt-build@0.1.0: opt-dep
Hello with opt-dep

% cargo run --no-default-features --features=opt_dep_b_ft  2>&1 | rg 'Hello|warn'
warning: tt-build@0.1.0: opt-dep
Hello with none

% cargo run --no-default-features --features=opt_dep_r_ft  2>&1 | rg 'Hello|warn'
warning: tt-build@0.1.0: none
Hello with opt-dep

this post was submitted on 14 Apr 2026

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