`#![feature]` may not be used on the stable release channel [closed] - rust

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I am trying to use the clap crate to do some argument parsing. However, when I add it to my Cargo.toml, I get the following error when I do cargo build:
$ cargo build
Compiling rustix v0.36.5
error[E0554]: `#![feature]` may not be used on the stable release channel
--> /home/wheeler/.cargo/registry/src/github.com-1ecc6299db9ec823/rustix-0.36.5/src/lib.rs:99:26
|
99 | #![cfg_attr(rustc_attrs, feature(rustc_attrs))]
| ^^^^^^^^^^^^^^^^^^^^
error[E0554]: `#![feature]` may not be used on the stable release channel
--> /home/wheeler/.cargo/registry/src/github.com-1ecc6299db9ec823/rustix-0.36.5/src/lib.rs:116:5
|
116 | feature(core_intrinsics)
| ^^^^^^^^^^^^^^^^^^^^^^^^
error[E0554]: `#![feature]` may not be used on the stable release channel
--> /home/wheeler/.cargo/registry/src/github.com-1ecc6299db9ec823/rustix-0.36.5/src/lib.rs:116:13
|
116 | feature(core_intrinsics)
| ^^^^^^^^^^^^^^^
For more information about this error, try `rustc --explain E0554`.
error: could not compile `rustix` due to 3 previous errors
There isn't anything in the documentation for clap that says that it requires the use of the nighly builds. I didn't understand why this was happening, so I created a VM to try to replicate the issue (using Vagrant). Here is the Vagrantfile:
Vagrant.configure("2") do |config|
config.vm.box = "generic/fedora37"
config.vm.provision "shell", inline: <<~'EOF'
set -e
set -x
sudo dnf update -y
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
source "$HOME/.cargo/env"
mkdir -p test-project
cd test-project
cat << 'EOFF' | sed -r 's/^ {2}//' > Cargo.toml
[package]
name = "rpg"
version = "0.1.0"
edition = "2021"
[dependencies]
clap = { version = "4.0.29", features = ["derive"] }
EOFF
cat Cargo.toml
mkdir -p src
cd src
touch main.rs
cat << 'EOFF' | sed -r 's/^ {2}//' > main.rs
use clap::Parser;
/// Simple program to greet a person
#[derive(Parser, Debug)]
#[command(author, version, about, long_about = None)]
struct Args {
/// Name of the person to greet
#[arg(short, long)]
name: String,
/// Number of times to greet
#[arg(short, long, default_value_t = 1)]
count: u8,
}
fn main() {
let args = Args::parse();
for _ in 0..args.count {
println!("Hello {}!", args.name)
}
}
EOFF
cat main.rs
cd ..
cargo build
EOF
end
But when I do vagrant up, the VM updates, installs rust, and compiles my little sample program just fine (it is the exact same main.rs and Cargo.toml I have on the host system).
Why does clap need the nightly version on my host machine, but not in my test VM?

Answer 1

There was something cached in the target directory that was causing this. I deleted the target directory and re-ran cargo build and the issue went away.

Answer 2

To use feature attribute, you need the nightly release channel. To switch to nightly, execute rustup default nightly command.