zerocopy-0.8.25 no longer builds on nightly

@rustbot

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 error

I 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

@rustbot

Thank you for the report! It would be useful to bisect the regression using cargo-bisect-rustc to make it easier to figure out what happened and ping the relevant people.
@rustbot label E-needs-bisection

@Noratrieb

@Noratrieb Sure I can give bisection a go. Never done rustc bisection before though. I see it takes dates, how do I figure out what nightly date beta corresponds to? As that is the latest known working version.

@petrochenkov

That's #144013, cc author @petrochenkov.

@rustbot label -E-needs-bisection

I tested a few random dates to find a starting point (I would still like to know a principled approach to this).

Regression starts with nightly-2025-07-19 (2025-07-18 works).

And then it gave the more detailed response:

Regression in b5df05d. Note that if it is a legacy rollup build, it might be available in rust-lang-ci@b5df05d.
The PR introducing the regression in this rollup is #144013: resolve: Make disambiguators for underscore bindings module…

searched nightlies: from nightly-2025-07-18 to nightly-2025-07-19
regressed nightly: nightly-2025-07-19
searched commit range: e466296...8f08b3a
regressed commit: 8231065

bisected with cargo-bisect-rustc v0.6.10

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2025-07-18 --end=2025-07-19

@petrochenkov

#144013 might be related cc @petrochenkov

#144013 might be related cc @petrochenkov

You aren't wrong, but you are late to party.

ah i only looked at the bisect output :D

Auto merge of #144238 - jhpratt:rollup-xb8aida, r=jhpratt

Reposting @lqd's MCVE from #144172 (comment) for ease-of-access:

it'll also be in UI tests when #144189 lands

Unrolled build for #144189

Rollup merge of rust-lang#144189 - lqd:test-144168, r=petrochenkov

Auto merge of rust-lang#144172 - lqd:revert-144013, r=petrochenkov

Auto merge of rust-lang#144238 - jhpratt:rollup-xb8aida, r=jhpratt

Rollup merge of #144189 - lqd:test-144168, r=petrochenkov

Auto merge of #144238 - jhpratt:rollup-xb8aida, r=jhpratt

Fix ASAN workflow: avoid zerocopy nightly incompatibility

fix: Disable ASAN job due to zerocopy nightly incompatibility

fix(ci): re-enable ASAN memory-safety workflow

Fix ASAN workflow: avoid zerocopy nightly incompatibility

fix: Disable ASAN job due to zerocopy nightly incompatibility

fix(ci): re-enable ASAN memory-safety workflow

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zerocopy-0.8.25 no longer builds on nightly #144168

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zerocopy-0.8.25 no longer builds on nightly #144168

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Noratrieb commented on Jul 19, 2025

VorpalBlade commented on Jul 19, 2025

lqd commented on Jul 19, 2025

VorpalBlade commented on Jul 19, 2025

matthiaskrgr commented on Jul 19, 2025

VorpalBlade commented on Jul 19, 2025

matthiaskrgr commented on Jul 19, 2025

23 remaining items

lqd commented on Jul 21, 2025

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