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Function type with opaque return type can be coerced to dyn Fn with arbitrary return type #98608
Description
I tried this code:
fn hi() -> impl Sized { std::ptr::null::<u8>() }
fn main() {
let b: Box<dyn Fn() -> Box<u8>> = Box::new(hi);
let boxed = b();
let null = *boxed;
println!("{null:?}");
}I expected to see this happen: Compiler error, since impl Sized cannot be coerced to Box<u8>.
Instead, this happened: Code compiles, segfault
Meta
rustc --version --verbose:
rustc 1.64.0-nightly (2f3ddd9f5 2022-06-27)
binary: rustc
commit-hash: 2f3ddd9f594adf9773547aa7cedb43c4ac8ffd2f
commit-date: 2022-06-27
host: x86_64-unknown-linux-gnu
release: 1.64.0-nightly
LLVM version: 14.0.6
Reacted by Michael Goulet, Frank Steffahn, Chayim Refael Friedman, Angel D. Munoz, Restioson, Alex Orlenko, Sean Dewar, Clément Nerma, Grégoire Geis, Hybras and 13 more
Reacted by Daniel Henry-Mantilla, 5hir0kur0, Sean Dewar, Johannes Dahlström, Grégoire Geis, Jonas Platte, zeb, Hybras, Coca, Robert and 6 more
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Category: This is a bug.Issue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/SoundnessCritical priorityRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.Performance or correctness regression from one stable version to another.
Activity
JakobDegen commentedon Jun 28, 2022
This regressed in 1.61, unfortunately my wifi is not currently up for running a proper bisect.
@rustbot label +regression-from-stable-to-stable
oli-obk commentedon Jun 28, 2022
likely cause is one of the uses of
take_opaque_typewithout actually registering the hidden typesDylan-DPC commentedon Jun 30, 2022
marking it as critical based on the prioritisation group discussion
apiraino commentedon Jun 30, 2022
Correct link for WG-prioritization Zulip discussion
rust: update to version 1.62.1.
lang/rust: update to version 1.62.1.
lang/rust: update to version 1.62.1.
lang/rust: update to version 1.62.1.
lang/rust: update to version 1.62.1.