Nightly regression with -Z build-std for wasm32-unknown-unknown

[daxpedda]

cargo build --target wasm32-unknown-unknown -Z build-std

Gives this error:

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

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

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

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

error: duplicate lang item in crate `core`: `slice_u8`.
  |
  = note: first defined in crate `core` (which `std` depends on).

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

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

error: duplicate lang item in crate `core`: `i8`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `i16`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `i32`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `i64`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `i128`.
  |
  = note: first defined in crate `core` (which `std` depends on).

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

error: duplicate lang item in crate `core`: `u8`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `u16`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `u32`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `u64`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `u128`.
  |
  = note: first defined in crate `core` (which `std` depends on).

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

error: duplicate lang item in crate `core`: `f32`.
  |
  = note: first defined in crate `core` (which `std` depends on).

error: duplicate lang item in crate `core`: `f64`.
  |
  = note: first defined in crate `core` (which `std` depends on).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

error: duplicate lang item in crate `core`: `not`.
  |
  = note: first defined in crate `core` (which `std` depends on).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

error: aborting due to 81 previous errors

error: could not compile `test-wasm`.

I have narrowed it down to this:
nightly-2019-12-21: works
nightly-2019-12-22: doesn't work anymore
nightly-2020-02-12 (current): still doesn't work

It does work with #![no_std] though.
Other target I tried that worked: x86_64-pc-windows-msvc.
Should I report this here: https://github.com/rust-lang/wg-cargo-std-aware?

[ehuss]

It is most helpful if build-std bugs are reported at https://github.com/rust-lang/wg-cargo-std-aware or https://github.com/rust-lang/cargo/issues/.

The issue here is that it currently does not know which panic strategy each platform requires, and assumes "unwind". wasm32 needs the "abort" strategy, which requires the panic_abort crate. You can run with -Zbuild-std=panic_abort,std.

This issue is tracked in rust-lang/wg-cargo-std-aware#29

[jonas-schievink]

Closing in favor of rust-lang/wg-cargo-std-aware#29 then

[daxpedda]

I just confirmed it, thanks!