[-Zbuild-std] Duplicate lang item with panic=abort

[phil-opp]

Combining a no-harness test with a panic=abort key in the Cargo.toml leads to duplicate lang item errors if compiled with cargo test -Zbuild-std=core.

Steps to Reproduce

MRE by @hoodmane from #15058

Make a folder with the following two files:

Cargo.toml

[package]
name = "test"
edition = "2024"

[profile.dev]
panic = "abort"

[[bin]]
name = "test"
path = "main.rs"

main.rs

pub fn main() { }

Bash

1. rustup install nightly-2025-01-13
2. cargo +nightly-2025-01-13 build -Zbuild-std

Result

   Compiling tmp v0.0.0 (/home/rchatham/Documents/programming/rust-wasm-eh-test-2)
error[E0152]: duplicate lang item in crate `core`: `sized`
  |
  = note: the lang item is first defined in crate `core` (which `std` depends on)
  = note: first definition in `core` loaded from /home/rchatham/Documents/programming/rust-wasm-eh-test-2/target/wasm32-unknown-emscripten/debug/deps/libcore-05cdacbb5559ef58.rlib, /home/rchatham/Documents/programming/rust-wasm-eh-test-2/target/wasm32-unknown-emscripten/debug/deps/libcore-05cdacbb5559ef58.rmeta
  = note: second definition in `core` loaded from /home/rchatham/.rustup/toolchains/nightly-2025-01-13-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libcore-9c3bca22b80bc54a.rlib

For more information about this error, try `rustc --explain E0152`.
error: could not compile `test` (bin "test") due to 1 previous error

Original MRE from the issue author

1. Create a new cargo project with the following contents:

   Cargo.toml:

   [package]
   name = "playground"
   version = "0.1.0"
   authors = ["Philipp Oppermann <dev@phil-opp.com>"]
   edition = "2018"
   
   [lib]
   harness = false
   
   [dependencies]
   
   [profile.dev]
   panic = "abort"     # it works if this line is removed

   src/lib.rs:

   #![no_std]
   #![cfg_attr(test, no_main)]
   
   #[cfg(test)]
   #[panic_handler]
   fn panic(_info: &core::panic::PanicInfo) -> ! {
       loop {}
   }

   target.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"
     }

2. Run cargo test --target target.json -Z build-std=core --no-run

   The following error occurs:

   cargo test --target target.json -Z build-std=core
    Compiling playground v0.1.0 (…)
    error: duplicate lang item in crate `core`: `bool`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `char`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `str`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `slice`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `slice_u8`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `const_ptr`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `mut_ptr`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `i8`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `i16`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `i32`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `i64`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `i128`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `isize`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `u8`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `u16`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `u32`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `u64`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `u128`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `usize`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `f32`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `f64`.
    |
    error: duplicate lang item in crate `core`: `bool`.
    = note: first defined in crate `core`.
    |
   
    error: duplicate lang item in crate `core`: `sized`.
    = note: first defined in crate `core`.
   
    |
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `char`.
   
    |
    error: duplicate lang item in crate `core`: `unsize`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `str`.
    |
    error: duplicate lang item in crate `core`: `copy`.
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `slice`.
    |
    error: duplicate lang item in crate `core`: `clone`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `slice_u8`.
   
    |
    error: duplicate lang item in crate `core`: `sync`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `const_ptr`.
   
    |
    error: duplicate lang item in crate `core`: `freeze`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `mut_ptr`.
   
    |
    error: duplicate lang item in crate `core`: `drop`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `i8`.
   
    |
    error: duplicate lang item in crate `core`: `coerce_unsized`.
    = note: first defined in crate `core`.
   
    |
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `i16`.
   
    |
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `dispatch_from_dyn`.
   
    |
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `i32`.
   
    |
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `add`.
   
    |
    error: duplicate lang item in crate `core`: `i64`.
    = note: first defined in crate `core`.
   
    |
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `sub`.
   
    |
    error: duplicate lang item in crate `core`: `i128`.
    = note: first defined in crate `core`.
   
    |
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `mul`.
   
    |
    error: duplicate lang item in crate `core`: `isize`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `div`.
   
    |
    error: duplicate lang item in crate `core`: `u8`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `rem`.
   
    |
    error: duplicate lang item in crate `core`: `u16`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `neg`.
    |
    error: duplicate lang item in crate `core`: `u32`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `not`.
    |
    error: duplicate lang item in crate `core`: `u64`.
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `bitxor`.
    |
    error: duplicate lang item in crate `core`: `u128`.
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `bitand`.
    |
    error: duplicate lang item in crate `core`: `usize`.
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `bitor`.
    error: duplicate lang item in crate `core`: `f32`.
    |
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `shl`.
    error: duplicate lang item in crate `core`: `f64`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `shr`.
    error: duplicate lang item in crate `core`: `sized`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `add_assign`.
    error: duplicate lang item in crate `core`: `unsize`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `sub_assign`.
    error: duplicate lang item in crate `core`: `copy`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `mul_assign`.
    error: duplicate lang item in crate `core`: `clone`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `div_assign`.
    error: duplicate lang item in crate `core`: `sync`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `rem_assign`.
    error: duplicate lang item in crate `core`: `freeze`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `bitxor_assign`.
    error: duplicate lang item in crate `core`: `drop`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `bitand_assign`.
    error: duplicate lang item in crate `core`: `coerce_unsized`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `bitor_assign`.
    error: duplicate lang item in crate `core`: `dispatch_from_dyn`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `shl_assign`.
    error: duplicate lang item in crate `core`: `add`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `sub`.
    error: duplicate lang item in crate `core`: `shr_assign`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `index`.
    error: duplicate lang item in crate `core`: `mul`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `index_mut`.
    error: duplicate lang item in crate `core`: `div`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `rem`.
    error: duplicate lang item in crate `core`: `unsafe_cell`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `neg`.
    |
    error: duplicate lang item in crate `core`: `va_list`.
    = note: first defined in crate `core`.
   
    |
    error: duplicate lang item in crate `core`: `not`.
    = note: first defined in crate `core`.
    |
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `bitxor`.
    |
    error: duplicate lang item in crate `core`: `deref`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `bitand`.
   
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `deref_mut`.
    error: duplicate lang item in crate `core`: `bitor`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `receiver`.
    error: duplicate lang item in crate `core`: `shl`.
    |
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `fn`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `fn_mut`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `fn_once`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `future_trait`.
    error: duplicate lang item in crate `core`: `shr`.
    |
    = note: first defined in crate `core`.
   
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `add_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `sub_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `mul_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `div_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `rem_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `bitxor_assign`.
    error: duplicate lang item in crate `core`: `generator_state`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `bitand_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `bitor_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `shl_assign`.
    |
    = note: first defined in crate `core`.
   
    |
    error: duplicate lang item in crate `core`: `shr_assign`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `index`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `index_mut`.
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `unsafe_cell`.
    |
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `generator`.
    error: duplicate lang item in crate `core`: `va_list`.
    |
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `deref`.
    |
    error: duplicate lang item in crate `core`: `unpin`.
    = note: first defined in crate `core`.
   
    |
    error: duplicate lang item in crate `core`: `deref_mut`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `receiver`.
    error: duplicate lang item in crate `core`: `pin`.
    |
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `fn`.
    |
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `eq`.
    error: duplicate lang item in crate `core`: `fn_mut`.
    |
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `fn_once`.
    |
    error: duplicate lang item in crate `core`: `partial_ord`.
    = note: first defined in crate `core`.
   
    |
    error: duplicate lang item in crate `core`: `future_trait`.
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `generator_state`.
    |
    error: duplicate lang item in crate `core`: `ord`.
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `generator`.
    |
    error: duplicate lang item in crate `core`: `panic`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `unpin`.
   
    |
    error: duplicate lang item in crate `core`: `panic_bounds_check`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `pin`.
   
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `eq`.
    error: duplicate lang item in crate `core`: `panic_info`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `partial_ord`.
    error: duplicate lang item in crate `core`: `drop_in_place`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `ord`.
    error: duplicate lang item in crate `core`: `alloc_layout`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `panic`.
    error: duplicate lang item in crate `core`: `phantom_data`.
    |
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `panic_bounds_check`.
    error: duplicate lang item in crate `core`: `manually_drop`.
    |
    |
    = note: first defined in crate `core`.
    = note: first defined in crate `core`.
   
   
    error: duplicate lang item in crate `core`: `panic_info`.
    error: duplicate lang item in crate `core`: `maybe_uninit`.
    |
    |
    = note: first defined in crate `core`.
   
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `drop_in_place`.
    |
    error: duplicate lang item in crate `core`: `align_offset`.
    = note: first defined in crate `core`.
    |
   
    = note: first defined in crate `core`.
    error: duplicate lang item in crate `core`: `alloc_layout`.
   
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `phantom_data`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `manually_drop`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `maybe_uninit`.
    |
    = note: first defined in crate `core`.
   
    error: duplicate lang item in crate `core`: `align_offset`.
    |
    = note: first defined in crate `core`.
   
    error: aborting due to 79 previous errors
   
    error: argument should be `&PanicInfo`
    --> src/lib.rs:6:17
    |
    6 | fn panic(_info: &core::panic::PanicInfo) -> ! {
    |                 ^^^^^^^^^^^^^^^^^^^^^^^
   
    error: Could not compile `playground`.
    warning: build failed, waiting for other jobs to finish...
    error: aborting due to 80 previous errors
   
    error: Could not compile `playground`.
   
    To learn more, run the command again with --verbose.
   

3. Remove the panic=abort line from the Cargo.toml

4. Rerun the command from step 2 (cargo test --target target.json -Z build-std=core --no-run). It works now.

My Guess

My guess is that the core library is somehow compiled twice when the panic=abort line is specified.

Version

cargo 1.39.0-nightly (fe0e5a4 2019-09-04)

[alexcrichton]

I think this is covered by rust-lang/wg-cargo-std-aware#29 for now where panic=abort isn't super well supported. Especially with cargo test things get funky because Cargo tries to compile some parts of the crate graph with panic=unwind instead of panic=abort. Overall in general the panic story isn't sorted out yet, so having more data points is good, thanks!

[phil-opp]

I don't think that any crates are compiled with unwinding in this example because the target itself specfies "panic-strategy": "abort". So the profile.dev.panic key is not needed at all for this example.

As another data point, I was able to successfully run cargo test -Zbuild-std=core,alloc for https://github.com/phil-opp/blog_os after deleting the superfluous profile.dev.panic key. So specifying panic=abort in the target JSON file seems to work without problems.

Feel free to close this in favor of the working group issue if you like.

[alexcrichton]

Oh true yeah, but Cargo compiles one with -Cpanic=unwind (which I guess is an ignored setting) and again with -Cpanic=abort so I think that's where the two lang items are coming from. In any case I'd like to keep this issue open as a concrete test case we'll want to fix when accounting for panic support with -Zbuild-std, there may be something fishy here that I'm not understanding fully yet.

[RReverser]

I'm seeing same error even without panic=abort when trying to build raytrace-parallel example from here https://github.com/rustwasm/wasm-bindgen/tree/master/examples/raytrace-parallel, but on Windows instead of Linux.

I'm not sure what are the platform differences, but so far none of custom build-std=... combinations seem to help :(

The closest I got was passing -Zbuild-std=...,alloc on the command line, but then Rust complains with

error: macro-expanded `extern crate` items cannot shadow names passed with `--extern`
  --> C:\Users\rreverser\.cargo\registry\src\mygithub.libinneed.workers.dev-1ecc6299db9ec823\crossbeam-epoch-0.7.2\src\lib.rs:72:9
   |
72 |         extern crate std as alloc;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^

because some crates like Crossbeam use cfg_if to alias std as alloc like

cfg_if! {
    if #[cfg(feature = "alloc")] {
        extern crate alloc;
    } else if #[cfg(feature = "std")] {
        extern crate std as alloc;
    }
}

and I'm not sure how to disable that check either.

[alexcrichton]

@RReverser that's a too-old version of Cargo, that issue should be fixed in nightlies.

[stevefan1999-personal]

I'm seeing same error even without panic=abort when trying to build raytrace-parallel example from here https://github.com/rustwasm/wasm-bindgen/tree/master/examples/raytrace-parallel, but on Windows instead of Linux.

I'm not sure what are the platform differences, but so far none of custom build-std=... combinations seem to help :(

The closest I got was passing -Zbuild-std=...,alloc on the command line, but then Rust complains with

error: macro-expanded `extern crate` items cannot shadow names passed with `--extern`
  --> C:\Users\rreverser\.cargo\registry\src\mygithub.libinneed.workers.dev-1ecc6299db9ec823\crossbeam-epoch-0.7.2\src\lib.rs:72:9
   |
72 |         extern crate std as alloc;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^

because some crates like Crossbeam use cfg_if to alias std as alloc like

cfg_if! {
    if #[cfg(feature = "alloc")] {
        extern crate alloc;
    } else if #[cfg(feature = "std")] {
        extern crate std as alloc;
    }
}

and I'm not sure how to disable that check either.

This is exactly the problem you described for what I encountered, and still not working using the latest version of nightly Rust as of the date of this comment.

[joshtriplett]

I can reproduce this with latest nightly, with just cargo new foo, adding a [profile.release] section that sets panic = "abort", and building with cargo build -Zbuild-std --release --target x86_64-unknown-linux-gnu.