Does not work in no-std environment

[koxu1996]

I am unable to compile my project due to found duplicate lang item panic_impl, which appears to be caused by std library being indirectly included by rasn 😨. Even though this library is claimed as no_std its dependencies are not!

Where std gets included?

Latest rasn v0.8.2 depends on custom nom parser with bitvec:

nom-bitvec = { package = "bitvec-nom2", version = "0.2.0" }

This need to be discussed. Why is it custom? Probably because upstream is not supporting bitvec v1 - see rust-bakery/nom-bitvec#1, and relevant PR got stuck. It seems that @XAMPPRocky released fork as renamed package with tag 0.2.0. The different between fork source code and files published in crates.io made my investigation more difficult.

Okay, so let's use crates.io as the source of truth. You can see that bitvec-nom2 depends on bitvec v1:

Default features are not disabled, so std gets included:

NOTE: I was able to track it down with cargo tree -e features.

[koxu1996]

The second place where std is indirectly included in rasn:

rasn/Cargo.toml

Line 49 in 1809d7c

snafu = { version = "0.7", default-features = false, features = ["backtraces"] }

You can see that snafu's backtraces feature is enabling it:

NOTE: snafu 0.8.0 removed this feature

[XAMPPRocky]

Thank you for your issue! This is definitely not intentional, we should disable std in my fork and put backtraces behind a feature that is disabled by default.

[koxu1996]

Also JER should be put behind a feature, as jzon is not no-std compatible as well.

[XAMPPRocky]

@koxu1996 Can you check now, as we now should compile with the latest nom-bitvec

[Nicceboy]

I hope that this is enough confirm that it works in no-std (tested on macOS):

Sample:

#![allow(internal_features)]
#![feature(lang_items)]
#![no_std]
#![no_main]

extern crate alloc;
use libc::printf;
use libc_alloc::LibcAlloc;
use rasn::prelude::*;

#[global_allocator]
static ALLOCATOR: LibcAlloc = LibcAlloc;

#[unsafe(no_mangle)]
// Use _start() on x86_64, main() on ARM
pub extern "C" fn main() -> ! {
    #[derive(Debug, AsnType, Encode, Decode)]
    struct Test {
        a: u8,
        b: u16,
        c: u32,
    }
    let sample = Test { a: 1, b: 2, c: 3 };
    let encoded = rasn::coer::encode(&sample).unwrap();

    unsafe {
        for &num in encoded.iter() {
            printf(c"%d\n".as_ptr() as *const _, num as i32);
        }
        libc::exit(0);
    }
}

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

// This is never called, but it is required by the linker
#[lang = "eh_personality"]
fn eh_personality() {}

build.rs

fn main() {
    println!("cargo:rustc-link-lib=c");
    println!("cargo:rustc-link-arg=-nostartfiles");
}

Cargo.toml

[package]
name = "nostd_sample"
version = "0.1.0"
edition = "2024"

[profile.dev]
panic = "abort"

[profile.release]
opt-level = 3
strip = true
debug = false
lto = true
codegen-units = 1
panic = "abort"

[dependencies]
libc = "0.2.167"
libc_alloc = "1.0.7"
rasn = "0.22.0"

[features]
default = ["alloc"]
alloc = []

Linked items:

otool -L target/release/nostd_sample
target/release/nostd_sample:
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1351.0.0)
        /usr/lib/libiconv.2.dylib (compatibility version 7.0.0, current version 7.0.0)

Size:

du -sh target/release/nostd_sample
 52K    target/release/nostd_sample

When not stripping and compiling with debug symbols, no mentions of std, other than alloc.