Enum layout should allow multiple untagged variants if they have nonoverlapping values
Open
Nobody has claimed this yet.
A-layout
C-optimization
T-compiler
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
I tried this code:
enum En1 {
Bool(bool),
Other(En2),
}
#[repr(u8)]
enum En2 {
Six = 6,
Seven = 7,
}
fn main() {
dbg!(size_of::<En1>());
}
I expected to see this happen: En1 has size 1
Instead, this happened: En1 has size 2
This will become more of an issue with range types on the horizon
Meta
rustc --version --verbose:
1.85.1
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 Rust reproducer in the issue and confirming the reported size of En1. Investigate the compiler's enum layout handling for untagged variants with nonoverlapping values; done means the example reports size 1 and the behavior is covered against regression.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100