Code
I tried this code:
$ cargo new reproducer
$ cd reproducer
$ cargo add zerocopy@=0.8.25
$ cargo +nightly build
Updating crates.io index
Locking 2 packages to latest Rust 1.90.0-nightly compatible versions
Downgrading zerocopy v0.8.26 -> v0.8.25 (available: v0.8.26)
Downgrading zerocopy-derive v0.8.26 -> v0.8.25 (available: v0.8.26)
Compiling zerocopy v0.8.25
error[E0428]: the name `_` is defined multiple times
--> /home/user/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/zerocopy-0.8.25/src/byteorder.rs:497:9
|
497 | const _: () = unsafe {
| ^^^^^^^^^^^^^^^^^^^^ `_` redefined here
...
734 | / define_type!(
735 | | A,
736 | | "A 64-bit unsigned integer",
737 | | U64,
... |
749 | | [U128]
750 | | );
| |_- in this macro invocation
|
::: /home/user/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/zerocopy-0.8.25/src/util/macros.rs:416:9
|
416 | const _: () = {
| ------------- previous definition of the value `_` here
|
= note: `_` must be defined only once in the value namespace of this module
= note: this error originates in the macro `define_type` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0428`.
error: could not compile `zerocopy` (lib) due to 1 previous errorI expected to see this happen: Build on nightly without having to update lock files. This will break so many cargo install --locked commands. For example: requiring me to make a new release for my Arch Linux package just for the package to keep working (even though the software hasn't changed otherwise, it is feature complete).
Instead, this happened: Build error as seen above.
zerocopy 0.8.26 does work, but again, that means every downstream binary project needs to release a new version so cargo install --locked keeps working.
Version it worked on
It most recently worked on:
rustc 1.88.0 (6b00bc388 2025-06-23)
binary: rustc
commit-hash: 6b00bc3880198600130e1cf62b8f8a93494488cc
commit-date: 2025-06-23
host: x86_64-unknown-linux-gnu
release: 1.88.0
LLVM version: 20.1.5
Also checked, it works on beta (1.89.0-beta.5).
Version with regression
rustc --version --verbose:
rustc 1.90.0-nightly (8f08b3a32 2025-07-18)
binary: rustc
commit-hash: 8f08b3a32478b8d0507732800ecb548a76e0fd0c
commit-date: 2025-07-18
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.8
Backtrace
N/A
@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged
Code
I tried this code:
I expected to see this happen: Build on nightly without having to update lock files. This will break so many
cargo install --lockedcommands. For example: requiring me to make a new release for my Arch Linux package just for the package to keep working (even though the software hasn't changed otherwise, it is feature complete).Instead, this happened: Build error as seen above.
zerocopy 0.8.26 does work, but again, that means every downstream binary project needs to release a new version so cargo install --locked keeps working.
Version it worked on
It most recently worked on:
Also checked, it works on beta (1.89.0-beta.5).
Version with regression
rustc --version --verbose:Backtrace
N/A
@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged