build_safely

Designed to help create good build scripts, with a focus on ease of use for you, valuable output in cargo build -vv & no annoying surprises for anyone downstream.

Usage

use build_safely::prelude::*;
// Result uses BuildError to give meaningful messages
fn main() -> Result<()> {
    // get an environment variable and re-run build script if it changes.
    let my_var: String = get_var("MY_VAR")?;
    // get values from an environment variable, separated by the
    // OS path separator and re-run build script if it changes.
    let my_vals: IndexSet<String> = split_var("MY_VALUES")?;
    if my_vals.contains("some_value") {
        unimplemented!("do something")
    }
    // get a new AutoCfg or provide a valuable error
    // rather than panicking.
    let ac = AutoCfg::new()?;
    // check to see if the downstream crate has defined
    // `unstable.allow-features` in `.cargo/config.toml`.
    // It is mandatory to perform this check and pass the
    // result to any calls to `emit_unstable_feature`
    let allowed_features = cargo_allowed_features()?;
    // We want to make use of `assert_matches` if it is available
    ac.emit_unstable_feature(assert_matches, &allowed_features);
    //                       ^^^^^^^^^^^^^^ - enum variant to avoid typos
    Ok(())
}

Prelude

use build_safely::prelude::*;

provides:

• A [Result] alias & [BuildError] type that gives meaningful output from main() -> Result<()>.
• [get_var()] & [split_var()] which automatically register cargo::rerun-if-env-changed and include the variable name in any errors.
• emit_unstable_feature(), cargo_allowed_features & enum UnstableFeature to provide a safe way to identify the availability of nightly features & handle the future stabilisation process without additional effort on your part. All while respecting any allow-features whitelists.

Note to downstream crates

If you (transiently) depend on a crate which uses build_safely and have implemented a whitelist of allowed-features.

Due to limitations in the information provided by cargo:

• This will obtain config.toml files based upon OUT_DIR. If this is not under the project root, you can override by providing an alternative path via the environment variable NINJA_CARGO_CONFIG_DIR. See cargo's documentation on config file hierarchical structure for more details.
• This will not respect additional entries passed at the command line via cargo --config unstable.allow-features=[...]