Document Error::{new,other} as to be avoided in pre_exec #148971
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Nov 15, 2025
| /// other threads perhaps still running when the `fork` was run). | ||
| /// | ||
| /// Note that the list of allocating functions includes [`Error::new`] and | ||
| /// [`Error::other`]. To signal a non-trivial error, prefer [`panic!`]. |
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Is panic safe to call? Won't it allocate the payload?
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This is answered by the existing documentation slightly below. TL;DR is that the message is printed, but without traceback; the panic hook is not invoked; and unwinding doesn't occur. So the payload doesn't need to be allocated.
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This is a mistake I've found in many projects on GitHub and made myself. It's obvious that
Error::new/Error::otherallocate when you look at their signatures, and it's obvious that thepre_execclosure shouldn't allocate, but when you're asked to write a closure that returns a specific type, you don't expect its main constructor to be problematic.I've included the list of 71 affected projects in a spoiler, though I don't expect anyone to look through it closely. It includes popular projects like alacritty, pika-backup, rio, rpm-ostree, and headcrab, as well as many smaller ones. For the most part, the snippets I've found are careful to only call functions from
libc,nix, orrustix, so it's not a case of general incompetence, but something that just slipped through the cracks.This docs section is already cluttered, so I've kept it terse.
If this is merged, I'd like to mass-post issues to the affected projects linking to this PR as a centralized source of information and place for discussion. Are there any objections about that?
@rustbot label +A-docs +A-process +O-unix +T-libs-api
List of affected projects
Format: links (witness of multi-threading)
tokio::main)thread::spawn)tokio::main)library)thread::spawn)tokio::runtime::Builder::new_multi_thread)tokio::main)actix_rt::main)thread::Builder::new)none)thread::spawn)tokio::main)thread::spawn)tokio::main)library)none)tokio::main)tokio::main)library)none)tokio::main)library)thread::spawn)tokio::runtime::Runtime::new())thread::spawn)tokio::main)thread::spawn)tokio::main)library)tokio::main)thread::spawn)thread::spawn)tokio::main)thread::spawn)thread::spawn)thread::spawn)tokio::main)tokio::main)none)none)thread::spawn)thread::spawn)tokio::main)async_std::task::spawn)tokio::main)tokio::main)library)none)thread::spawn)library)thread::spawn)thread::spawn)gtk)thread::spawn)library)library)thread::spawn)thread::spawn)library)library)thread::spawn)tokio::main)tokio::main)tokio::main)none)tokio::main)library)tokio::main)none)tokio::main)library)