Incorrect build issue displayed: "found duplicate lang item panic_impl"

[jackgerrits]

I am following the writing an OS in Rust tutorials and in the first section it describes creating a no_std binary and you must specify the panic handler. The following code compiles file but rust-analyzer believes there is an error and shows it in VSCode.

#![no_std]
#![no_main]

use core::panic::PanicInfo;

/// This function is called on panic.
#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

#[no_mangle]
pub extern "C" fn _start() -> ! {
    loop {}
}

found duplicate lang item `panic_impl`
the lang item is first defined in crate `std` (which `test` depends on)rustc(E0152)

I tried setting the target to one that doesn't link with the OS, settings.json:

 "rust-analyzer.cargo.target": "thumbv7em-none-eabihf"

Rust-analyzer extension version: 0.2.166

[edwin0cheng]

This error is coming from rustc, what's the result if you run cargo check in the terminal ?

[jackgerrits]

I added a custom target and updated .cargo/config to be:

[build]
target = "x86_64-rustos.json"

and defined the target as follows:

//x86_64-rustos.json
{
    "llvm-target": "x86_64-unknown-none",
    "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
    "arch": "x86_64",
    "target-endian": "little",
    "target-pointer-width": "64",
    "target-c-int-width": "32",
    "os": "none",
    "executables": true,
    "linker-flavor": "ld.lld",
    "linker": "rust-lld",
    "panic-strategy": "abort",
    "disable-redzone": true,
    "features": "-mmx,-sse,+soft-float"
}

This fixed the initial error from the issue. However, when I run cargo check and also in VSCode it displays this error:

    Checking rustos v0.1.0 (/home/jack/w/repos/rust-os-copy)
error[E0463]: can't find crate for `core`
  |
  = note: the `x86_64-rustos-6314987440205109011` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: could not compile `rustos`.

To learn more, run the command again with --verbose.

When I actually build the project I must use xbuild/xcheck because the custom target I have defined of course does not have the pre-built core crate included with the compiler. So the x-command builds core along with the target itself for the specified default target.

How does rust-analyzer deal with project that must be cross built and cannot be built directly for the host OS?

[edwin0cheng]

You can change the checkOnSave. settings, for example for rustc development:

{
    "rust-analyzer.checkOnSave.overrideCommand": [
        "./x.py",
        "check",
        "--json-output"
    ]
}

In your case, maybe something like this will works:

{
    "rust-analyzer.checkOnSave.overrideCommand": [
        "./cargo",
        "xcheck",
        "--json-output"
    ]
}

(Not sure xcheck support --json-output)

[jackgerrits]

Yes, that looks like it has resolved it.

Thanks so much for your reply and also for your work on rust-analyzer. It is a fantastic project!

[thorlucas]

I'm a bit confused as to the solution. Where is this checkOnSave attribute overridden? Can I do this on a per project basis?

[bjorn3]

ctrl-shift-p > "Preferences: Open Settings (JSON)" for the global settings. ctrl-shift-p > "Preferences: Open Workspace Settings (JSON)" or .vscode/settings.json for the workspace settings.

[thorlucas]

I'm not on VSCode. I'm using coc-rust-analyzer. Is this an IDE specific thing?

[bjorn3]

Is this an IDE specific thing?

Yes, every IDE has it's own way to pass settings to a language server.

[naveedpash]

I'm not on VSCode. I'm using coc-rust-analyzer. Is this an IDE specific thing?

You're using neovim yes?

:CocConfig<CR>

Then copy and paste @edwin0cheng 's response

:)

[lf-]

Hi! I'm also getting this, but my cargo check displays no error output on a x86_64-unknown-linux-gnu. I am developing a very thin rust program indeed, but it is running on Linux rather than bare metal (it's shellcode, for a CTF challenge, injected into a x86_64 Linux process). How can I continue debugging this?

.cargo/config:

[build]
rustflags = ["-C", "link-arg=-nostdlib", "-C", "link-arg=-static"]

src/main.rs:

#![no_std]
#![no_main]

#[panic_handler]
fn panic(_: &core::panic::PanicInfo) -> ! {
    loop {}
}

#[no_mangle]
fn _start() -> ! {
    loop {}
}

Cargo.toml:

[package]
name = "shellcode"
edition = "2018"
version = "0.0.0"

[profile.dev]
panic = "abort"

[profile.release]
panic = "abort"

[bjorn3]

Does cargo check --all-targets result in an error? If so you can set rust-analyzer.checkOnSave.allTargets to false.

[lf-]

@bjorn3 you hit the nail right on the head! I just found this independently with bpftrace's execsnoop before looking at GitHub again 😅.

Thanks!

[briankung]

Does anyone know how to set rust-analyzer.checkOnSave.allTargets to false for Sublime Text users?

[andyduplain]

Sorry to necro this issue, but I had the same issue as the OP and I think I solved it using #[cfg(not(test))]:

#[cfg(not(test))]
#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

The function is then greyed-out within VSCode.

[pacifi5t]

I recently had the same issue when using rust-analyzer (v0.3.1348) and CLion with a Rust plugin. I was targeting my MCU, so the solution was to set the target in project-directory/.cargo/config

[build]
target = "thumbv7em-none-eabihf"

[ghost]

Sorry to necro this issue, but I had the same issue as the OP and I think I solved it using #[cfg(not(test))]:

#[cfg(not(test))]
#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

The function is then greyed-out within VSCode.

i did as you mentioned

#![no_std]
#![no_main]
#![allow(unused_imports)]

use core::panic::PanicInfo;

#[no_mangle]
pub extern "C" fn _start() -> ! {
    loop {}
}

#[cfg(not(test))]
#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

but i don't think its the best way to handle the warning

[KjetilIN]

You can change the checkOnSave. settings, for example for rustc development:

{
    "rust-analyzer.checkOnSave.overrideCommand": [
        "./x.py",
        "check",
        "--json-output"
    ]
}

In your case, maybe something like this will works:

{
    "rust-analyzer.checkOnSave.overrideCommand": [
        "./cargo",
        "xcheck",
        "--json-output"
    ]
}

(Not sure xcheck support --json-output)

Worked for me! Thanks!