parallel compiler: async fns not reproducible
Nobody has claimed this yet.
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
I tried this code:
async fn test1(_: &'_ u8) {}
async fn test2<'s>(_: &'s u8,) {}
fn main() {}
rustc --edition=2024 -Zremap-cwd-prefix=reproducible_dir -Ccodegen-units=1 -Zthreads=30 --crate-type=lib --crate-name=test -o out ; md5sum out
I expected to see this happen:
constant md5sum
Instead, this happened:
the md5sum is flipflopping between d1afc31db4a80828c5c3937fae627a66 and 56d12483eea2eaaca0cd435f83439b59
Meta
rustc --version --verbose:
rustc 1.100.0-nightly (5db7f4be8 2026-09-01)
binary: rustc
commit-hash: 5db7f4be8a36c1b8ae19299469e2be2b0f052c21
commit-date: 2026-09-01
host: x86_64-unknown-linux-gnu
release: 1.100.0-nightly
LLVM version: 23.1.0
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by compiling the two async functions with the reported rustc command, including --edition=2024, -Zremap-cwd-prefix, -Ccodegen-units=1, and -Zthreads=30, then compare the output hashes across runs. Done means the generated library produces a consistent md5sum instead of alternating between the two reported values.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100