Rust build error: unknown `--json` option `future-incompat`

Question

I am trying to build a basic application for the Adafruit CLUE using Rust.

When using the peripheral access crate (PAC) everything works fine, but I would like to use the HAL crate from Nordic Semiconductors.

I set up a very basic project which uses their nrf52840-hal crate. When running cargo build, I get the following error (full build log with --verbose):

    Updating crates.io index
   Compiling semver-parser v0.7.0
   Compiling cortex-m v0.7.4
   Compiling proc-macro2 v1.0.37
   Compiling nb v1.0.0
   Compiling unicode-xid v0.2.3
   Compiling syn v1.0.92
   Compiling vcell v0.1.3
   Compiling void v1.0.2
   Compiling bitfield v0.13.2
   Compiling cortex-m-rt v0.7.1
   Compiling critical-section v0.2.7
   Compiling typenum v1.15.0
info: syncing channel updates for 'nightly-2021-08-18-x86_64-unknown-linux-gnu'
   Compiling az v1.2.0
   Compiling nrf52840-pac v0.11.0
info: latest update on 2021-08-18, rust version 1.56.0-nightly (30a0a9b69 2021-08-17)
   Compiling fixed v1.15.0
   Compiling cfg-if v1.0.0
info: component 'rust-src' is up to date
info: component 'rust-std' for target 'riscv32imac-unknown-none-elf' is up to date
info: component 'rust-std' for target 'riscv32imc-unknown-none-elf' is up to date
info: component 'rust-std' for target 'thumbv6m-none-eabi' is up to date
info: component 'rust-std' for target 'thumbv7em-none-eabi' is up to date
info: component 'rustfmt' for target 'x86_64-unknown-linux-gnu' is up to date
warning: Force-skipping unavailable component 'rust-std-avr-specs/avr-atmpeg328p.json'
   Compiling bare-metal v1.0.0
error: unknown `--json` option `future-incompat`

   Compiling half v1.8.2
error: could not compile `critical-section`
warning: build failed, waiting for other jobs to finish...
error: build failed

I am using rustup with the stable toolchain on Ubuntu 20.04 (using nighly 2022-05-03 does not change anything to the error message). Rustup version output is:

rustup 1.24.3 (ce5817a94 2021-05-31)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.60.0 (7737e0b5c 2022-04-04)`

The full project is available here.

My .cargo/config.toml file is:

[build]
target = "thumbv7em-none-eabihf"
rustflags = [
  "-C", "link-arg=-Tlink.x",
]

The Cargo.toml is:

[package]
name = "hal-test"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cortex-m-rt = "0.7.1"
nrf52840-hal = "0.15.0"
panic-halt = "0.2.0"

and the src/main.rs file is:

#![no_std]
#![no_main]

use panic_halt as _;

#[cortex_m_rt::entry]
fn main() -> ! {
    loop {}
}

I tried to go through the dependency tree but I failed to find where this future-incompat option is added, given that it is passed plenty of times to rustc and it succeeds.

I would appreciate any pointers as to where to look further.

Update 2022-05-06: building the project with the exact same toolchain version on Ubuntu 21.04 works, I'll have to investigate further.

Answer 1

The issue was fixed by switching away from the rustup snap and using the recommended installation method of running the shell script (https://www.rust-lang.org/tools/install).