duplicate item in crate `core`

[chaozju]

I am testing with hello world case for build-std feature

my code

fn main() {
    println!("Hello, world!");
    println!("3 + 4 = {}",3+4);
}

then got

cargo +nightly build -Z build-std \
--release --target x86_64-unknown-linux-gnu
   Compiling compiler_builtins v0.1.25
   Compiling core v0.0.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore)
   Compiling cc v1.0.50
   Compiling libc v0.2.66
   Compiling autocfg v0.1.7
   Compiling std v0.0.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd)
   Compiling hashbrown v0.6.2
   Compiling backtrace-sys v0.1.32
   Compiling unwind v0.0.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libunwind)
   Compiling rustc-std-workspace-core v1.99.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/tools/rustc-std-workspace-core)
   Compiling cfg-if v0.1.10
   Compiling alloc v0.0.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc)
   Compiling rustc-demangle v0.1.16
   Compiling panic_abort v0.0.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libpanic_abort)
   Compiling backtrace v0.3.44
   Compiling rustc-std-workspace-alloc v1.99.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/tools/rustc-std-workspace-alloc)
   Compiling panic_unwind v0.0.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libpanic_unwind)
   Compiling proc_macro v0.0.0 (/home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro)
   Compiling hello v0.1.0 (/home/chao/rust-playground/hello)
error: duplicate lang item in crate `core`: `bool`.
  |
  = note: the lang item is first defined in crate `core` (which `std` depends on)

error: duplicate lang item in crate `core`: `char`.
  |
  = note: the lang item is first defined in crate `core` (which `std` depends on)

error: duplicate lang item in crate `core`: `str`.
  |
  = note: the lang item is first defined in crate `core` (which `std` depends on)

error: duplicate lang item in crate `core`: `slice`.
  |
  = note: the lang item is first defined in crate `core` (which `std` depends on)

and

error[E0277]: the size for values of type `()` cannot be known at compilation time
 --> src/main.rs:3:27
  |
3 |     println!("3 + 4 = {}",3+4);
  |                           ^^^ doesn't have a size known at compile-time
  |
  = help: the trait `std::marker::Sized` is not implemented for `()`
  = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
  = note: required by `std::result::Result`
  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the size for values of type `std::fmt::Error` cannot be known at compilation time
 --> src/main.rs:3:27
  |
3 |     println!("3 + 4 = {}",3+4);
  |                           ^^^ doesn't have a size known at compile-time
  |
  = help: the trait `std::marker::Sized` is not implemented for `std::fmt::Error`
  = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
  = note: required by `std::result::Result`
  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the size for values of type `{integer}` cannot be known at compilation time
   --> src/main.rs:3:5
    |
3   |     println!("3 + 4 = {}",3+4);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    | 
   ::: /home/chao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/fmt/mod.rs:281:20
    |
281 |     pub fn new<'b, T>(x: &'b T, f: fn(&T, &mut Formatter<'_>) -> Result) -> ArgumentV1<'b> {
    |                    - required by this bound in `std::fmt::ArgumentV1::<'a>::new`
    |
    = help: the trait `std::marker::Sized` is not implemented for `{integer}`
    = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 84 previous errors

For more information about this error, try `rustc --explain E0277`.
error: could not compile `hello`.

To learn more, run the command again with --verbose.
Makefile:18: recipe for target 'x86_64-gnu' failed
make: *** [x86_64-gnu] Error 101

[ehuss]

Hm, I can't seem to reproduce. What version of nightly are you using?

[chaozju]

@ehuss Hi, My toolchain info is

chao@DESKTOP-B79IRTG:~/rust-playground/hello$ rustup show
Default host: x86_64-unknown-linux-gnu
rustup home:  /home/chao/.rustup

installed toolchains
--------------------

stable-x86_64-unknown-linux-gnu (default)
nightly-x86_64-unknown-linux-gnu
1.40.0-x86_64-unknown-linux-gnu

installed targets for active toolchain
--------------------------------------

riscv64gc-unknown-linux-gnu
riscv64gc-unknown-none-elf
wasm32-wasi
x86_64-unknown-linux-gnu
x86_64-unknown-linux-musl

active toolchain
----------------

stable-x86_64-unknown-linux-gnu (default)
rustc 1.42.0 (b8cedc004 2020-03-09)

[ehuss]

That doesn't show the nightly version you are using. rustc +nightly -V shows which nightly version you have.

[chaozju]

@ehuss

OOPS

chao@DESKTOP-B79IRTG:~/rust-playground/hello$ rustc +nightly -V
rustc 1.44.0-nightly (f509b26a7 2020-03-18)

[ehuss]

2020-03-18 This is quite old. Can you try with the latest nightly? rustup update nightly can be used to update.

[chaozju]

@ehuss same error after updating nightly

[ehuss]

Which exact version did you use?

[chaozju]

@ehuss rustc 1.46.0-nightly (feb3536eb 2020-06-09)

[dbdr]

I'm getting the same error with 1.46.0-nightly (0c03aee8b 2020-07-05) and panic="abort" in Cargo.toml. Changing panic to "unwind" removes the error.

@chaozju, did you use panic="abort"?

panic="abort" also works when using -Z build-std=panic_abort,std, as suggested by @alexcrichton in #29.

[chaozju]

@dbdr It works, THX

[gmorer]

Hi, I got the same error with rustc 1.51.0-nightly (04caa632d 2021-01-30) and adding a dependencie:

Cargo.toml:

[package]
name = "rust_issue"
version = "0.1.0"
authors = ["gmorer"]
edition = "2018"

[lib]
crate-type = ["lib"]

[profile.dev]
panic = "abort"

[profile.release]
panic = "abort"

[dependencies]
wasm-bindgen = "0.2"

src/lib.rs:

#![no_std]

extern crate alloc;
use alloc::boxed::Box;

pub fn my_fn() -> i32 {
    let mem = Box::new(4);
    *mem
}

compile line:

cargo build --target=wasm32-unknown-unknown  -Z build-std=alloc,panic_abort

Got the following error:

$> cargo build --target=wasm32-unknown-unknown  -Z build-std=alloc,panic_abort
   Compiling core v0.0.0 (/home/me/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
  [...]
   Compiling panic_abort v0.0.0 (/home/me/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/panic_abort)
   Compiling rust_issue v0.1.0 (/home/me/gits/rust_issue)
error: duplicate lang item in crate `core` (which `alloc` depends on): `bool`.
  |
  = note: the lang item is first defined in crate `core` (which `rust_issue` depends on)
  = note: first definition in `core` loaded from /home/me/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-unknown/lib/libcore-73412d1456c20040.rlib
  = note: second definition in `core` loaded from /home/me/gits/rust_issue/target/wasm32-unknown-unknown/debug/deps/libcore-d3db196937483bcf.rmeta

error: duplicate lang item in crate `core` (which `alloc` depends on): `char`.
  |
  = note: the lang item is first defined in crate `core` (which `rust_issue` depends on)
  = note: first definition in `core` loaded from /home/me/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-unknown/lib/libcore-73412d1456c20040.rlib
  = note: second definition in `core` loaded from /home/me/gits/rust_issue/target/wasm32-unknown-unknown/debug/deps/libcore-d3db196937483bcf.rmeta

error: duplicate lang item in crate `core` (which `alloc` depends on): `str`.
  |
  = note: the lang item is first defined in crate `core` (which `rust_issue` depends on)
  = note: first definition in `core` loaded from /home/me/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-unknown/lib/libcore-73412d1456c20040.rlib
  = note: second definition in `core` loaded from /home/me/gits/rust_issue/target/wasm32-unknown-unknown/debug/deps/libcore-d3db196937483bcf.rmeta

[ehuss]

@gmorer you have to ensure your dependencies do not use std if you are not building std. wasm-bindgen has a default std feature, so it has to be turned off:

wasm-bindgen = {version="0.2", default-features=false}

However, it looks like wasm-bindgen is broken in no_std environments. This line assumes mem:: is available, but it is gated here.

[ehuss]

I'm going to close as it isn't clear that there is an issue here. Better panic support is tracked in #29, and it looks like the wasm_bindgen issue was an issue with an external package.