CODEWITHSUNDEEP
rustrust-cargowasm-bindgen
user964375
user964375

Reputation: 2441

Enable a Cargo feature by default when the target arch is WASM?

Part of my Cargo.toml for my crate:

[features]
wasm = ["ed25519-dalek/nightly", "rand/wasm-bindgen", "js-sys"]

This works, when the crate is used in another project, and the "wasm" feature is explicitly chosen.

I want to automatically enable this feature only when the target arch is WASM. I tried adding this:

#[cfg(target_arch = "wasm32")]
default = ["wasm"]

When I compile for a target other than WASM, "wasm" is included as the default, how can I make "wasm" the default only when the target is WASM?

Upvotes: 11

Views: 6878

Answers (2)

Uttarayan
Uttarayan

Reputation: 191

I had the same issue.

I ended up using build.rs to enable features when a specific target is used.

[target.'cfg(all(target_arch = "wasm32", target_os = "unknown"))'.dependencies]
web-sys = { version = "0.3.64", features = ["Storage", "Window", "console"] }

[features]
sqlite = ["dep:rusqlite", "dbson/rusqlite"]
gui = []
default = ["gui"]

wasm = []

build.rs

pub fn main() {
    if std::env::var("TARGET").expect("Unable to get TARGET").contains("wasm32") {
        println!("cargo:rustc-cfg=feature=\"wasm\"");
    }
}

Here I wanted to enable wasm feature when the target is wasm32-unknown-unknown.

Note that this is not supported by cargo and this is run after dependency resolution.

So If I made web-sys optional and used wasm = ["dep:web-sys"] as a feature that wouldn't work.

Upvotes: 1

Boiethios
Boiethios

Reputation: 42849

You can only have target-specific dependencies, not target-specific features. This is a known bug that is unfortunately opened since 2015.

People expects this syntax to be supported, but right now there is nothing scheduled to make this work:

[target.'cfg(target_arch = "wasm32")'.features]
default = ["ed25519-dalek/nightly", "rand/wasm-bindgen", "js-sys"]

As a ugly workaround, you can create another crate that depends on your crate and let the user use this new crate:

[target.'cfg(target_arch = "wasm32")'.dependencies.your_crate]
version = "1.0.0"
features = ["wasm"]

Upvotes: 10

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