Guaranteed early breaks out of try blocks can't infer never type
Open
Nobody has claimed this yet.
A-inference
C-bug
F-never_type
F-try_blocks
S-has-mcve
T-compiler
T-lang
T-types
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
I tried this code:
#![feature(try_blocks)]
fn bug_repro() {
None = try {
return; // The semicolon is important!
};
}
#![feature(try_blocks)]
fn bug_repro() {
None = try {
None?;
return;
};
}
I expected to see this happen: The code compiles. This pattern is irrefutable
Instead, this happened: The pattern is marked as refutable and this code doesn't compile
Meta
rustc --version --verbose:
rustc 1.99.0-nightly (12c36e253 2026-08-10)
binary: rustc
commit-hash: 12c36e2539c54397c51d6ea4401defd8768a4f5b
commit-date: 2026-08-10
host: aarch64-apple-darwin
release: 1.99.0-nightly
LLVM version: 23.1.0
Zulip thread: #t-lang > Changing desugaring of try blocks
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 minimal try-block examples from the issue on the reported nightly and compare their pattern-refutability diagnostics. Then trace the compiler's try-block handling and never-type inference for guaranteed early exits; done means both examples compile with the pattern treated as irrefutable.
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
- 48/100