I tried to make 'Hello World' in Rust using this tutorial, but the build command is a bit verbose:
cargo +nightly build --target wasm32-unknown-unknown --release
Is it possible to set the default target for cargo build?
You could use a Cargo configuration file to specify a default target-triple for your project. In your project's root, create a .cargo directory and a config.toml file in it with the following contents:
[build]
target = "wasm32-unknown-unknown"
As listed in the Cargo documentation, you can create a .cargo/config and specify the target:
[build]
target = "my-custom-target"
If you're able to use unstable features, following documentation and especially per-package-target feature add this to you crate manifest that usually named Cargo.toml
cargo-features = ["per-package-target"]
[package]
forced-target = "wasm32-unknown-unknown"
# and/or:
default-target = "wasm32-unknown-unknown"
This requires nightly toolchain.
Related
I have installed both nightly and stable rust toolchains and make some -Z ... compile flags for nightly, but the stable rust can't recognize it and stops compiling; is there a way or a cargo directive to conditionally switch between nightly/stable rust compiler.
In .cargo/config.toml file
[build]
rustflags = [
"-C...",
"-Z...",
]
For nightly rust read -Z and -C flags, for stable rust only read -C or ignore -Z completely. So that, we can use cargo +stable/+nightly build without modify config.toml file every time.
Thanks Ruster ~
I don't think it's possible to specify rustc unstable feature inside config.toml but you can specify cargo unstable feature. It could be nice to have.
You could create a "nightly" directory:
cd my_rust_project
mkdir my_nightly_project
cd my_nightly_project
rustup override set nightly
Then using merge feature of config file of cargo you create you can override the global config using a my_nightly_project/.cargo/config.toml file.
Consider using alias instead.
According to the archival notice in wasm-gc,
The wasm-pack (and wasm-bindgen) project will already run [--gc-targets] by default for you, so there's no need to run it again.
How do we specify this in Cargo.toml explictly?
Rustc passes arguments with
-C, --codegen OPT[=VALUE]
Set a codegen option
The codegen option you want link-arg so you'd use it like -C link-arg=--gc-targets you can set that up in your Cargo.toml with,
[[bin]]
rustflags = [
"-C", "link-arg=--gc-targets",
]
Alternatively, you can now set this up directly with the new experimental extra-link-arg option in Cargo.
The program I'm writing runs much faster when the -C target-cpu=native flag is passed to rustc. I want to give users a simple, platform-independent way to enable this when compiling, so I added a Cargo feature cpu_native = [] in Cargo.toml and created this Cargo config in my project:
[target.'cfg(cpu_native)']
rustflags = ["-C", "target-cpu=native"]
However, this has no effect on my program, and passing --features cpu_native to Cargo does not even trigger a recompile. Changing to the following Cargo config does force re-compilation with faster instructions:
[build]
rustflags = ["-C", "target-cpu=native"]
However, this will compile with target-cpu=native with the default Cargo features, which was not what I wanted. From the Cargo book, what I want seems to be possible, but I don't see what I'm doing wrong.
I don't think this is supported (yet?). I enhanced Cargo to print out what config flags are checked against when resolving:
[
Name("debug_assertions"),
Name("proc_macro"),
KeyPair("target_arch", "x86_64"),
KeyPair("target_endian", "little"),
KeyPair("target_env", ""),
KeyPair("target_family", "unix"),
KeyPair("target_os", "macos"),
KeyPair("target_pointer_width", "64"),
Name("unix"),
]
[target.'cfg(cpu_native)']
This is the incorrect syntax for a Cargo feature; it would normally be cfg(feature = "cpu_native").
I put this in my Cargo.toml
[build]
target-dir = "../my-target"
However, Cargo doesn't recognize this key.
cargo run --release --bin my_project
warning: unused manifest key: build
error: failed to open: /.../project-root/target/releases/.cargo-lock
Caused by:
Permission denied (os error 13)
The custom target dir with the environment variable works:
CARGO_TARGET_DIR=../my-target cargo run --bin my_project
but how can I specify '../my-target' in Cargo.toml?
[build] is a Cargo-level configuration rather than for the project:
This document will explain how Cargo’s configuration system works, as well as available keys or configuration. For configuration of a project through its manifest, see the manifest format.
Put your [build] inside $PROJECT_DIR/.cargo/config or even $HOME/.cargo/config. See the above link for all the options.
Use the CARGO_TARGET_DIR environment variable:
CARGO_TARGET_DIR=../my-target cargo run --bin my_project
(This is stated in the question, but I wanted to highlight it for anyone that skips over that)
I want to conditionally compile my source code using cfg with Cargo,
after Googling for a while,
it seems that the solution is to use cargo --features.
http://doc.crates.io/manifest.html
I tried adding a few
#[cfg(feature = "foo")]
in the source code and
cargo build --features foo
, but it says
Package `xxx v0.0.1 (file:///C:/yyy/xxx)` does not have these features: `foo`
How can I let cargo identify the features? Do I have to add something in Cargo.toml?
Here's the version of rustc and cargo I am using:
C:\>rustc --version
rustc 0.13.0-nightly (42deaa5e4 2014-12-16 17:51:23 +0000)
C:\>cargo --version
cargo 0.0.1-pre-nightly (5af754d 2014-12-18 01:50:48 +0000)
You have to introduce the existing features in your Cargo.toml.
I was able to conditionally compile by doing the following:
In Cargo.toml, create a features section and introduce a certain feature name:
[features]
customfeature = [] # feature has no explicit dependencies
If you want your feature to have specific dependencies check the examples in the documentation.
In your code, use #[cfg(feature="customfeature")]
Run cargo build --features customfeature
Since your steps 2 & 3 seem to be fine, there must probably be a problem with your Cargo.toml.
As stated in other answers, you can use features for this. I would like to add that features do not only allow you to conditionally compile parts of your code but also to conditionally include dependencies that may be part of that code. Consider the following snippets:
You can activate the conditional code using a feature flag as already described in other anwsers:
cargo build --features customfeature
You need to mark your conditional code to exist only when your customfeature is enabled:
#[cfg(feature = "customfeature")]
fn my_func() {
my_optional_dependency::do_something();
}
// This includes dependencies only when customfeature is enabled
#[cfg(feature = "customfeature")]
extern crate my_optional_dependency;
....
#[cfg(feature = "customfeature")]
use my_optional_dependency::*;
....
Your Cargo.toml needs to have the following sections:
[dependencies.my_optional_dependency]
version = "1.2.3"
optional = true
[features]
customfeature = ["my_optional_dependency"]
This allows you to activate certain parts of your code along with their dependencies only if a feature is enabled.
Alternatively, you could create a cargo configuration file in your project, by creating a .cargo subdir in your project main folder, adding in it a config.toml file,
then inserting this section in .cargo/config.toml:
[build]
rustflags = "--cfg my_cfg_flag"
This will make cargo call rustc with flags --cfg my_cfg_flag
See here for details:
https://doc.rust-lang.org/cargo/reference/config.html