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A-edition-2024Area: The 2024 editionArea: The 2024 editionA-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.Area: Lints (warnings about flaws in source code) such as unused_mut.C-bugCategory: This is a bug.Category: This is a bug.I-edition-triagedIssue: This issue has been reviewed and triaged by the Edition team.Issue: This issue has been reviewed and triaged by the Edition team.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.
Description
I ran cargo +nightly fix --edition
on this code:
pub fn spawn_child() {
let _status = Command::new("some_program")
.before_exec(|| {
unsafe {
// Make the child process its own process group leader
if libc::setpgid(0, 0) != 0 {
return Err(std::io::Error::last_os_error());
}
Ok(())
}
})
.status();
}
And it made the following changes:
pub fn spawn_child() {
// TODO: Audit that the closure is async-signal-safe.
let _status = unsafe { Command::new("some_program")
.before_exec(|| {
unsafe {
// Make the child process its own process group leader
if libc::setpgid(0, 0) != 0 {
return Err(std::io::Error::last_os_error());
}
Ok(())
}
}) }
.status();
}
The output is unsatisfying in a few ways:
- There are now two
unsafe
blocks, triggering theunused_unsafe
lint. before_exec
is still deprecated, so perhaps it should just be replaced withpre_exec
?- The formatting is a bit weird; The newly added braces should get additional line breaks.
- The code doesn't compile once I add
edition = "2024"
toCargo.toml
:
error[E0716]: temporary value dropped while borrowed
--> src/lib.rs:7:9
|
7 | Command::new("some_program").before_exec(|| {
| -^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| _________creates a temporary value which is freed while still in use
| |
8 | | unsafe {
9 | | // Make the child process its own process group leader
10 | | if libc::setpgid(0, 0) != 0 {
... |
14 | | }
15 | | })
| | -
| | |
| |__________temporary value is freed at the end of this statement
| borrow later used here
|
= note: consider using a `let` binding to create a longer lived value
I wouldn't have submitted an issue based on the first three, but since cargo fix
is responsible for the new structure of the code, it seems like the failure to compile should have been avoidable.
I am confused about why this doesn't build. Why does pre_exec
/ before_exec
cause there to be a dropped-while-borrowed temporary under the 2024 edition where none existed previously?
To repair the broken build, I guess something like this is required? (The let mut cmd
part.)
pub fn spawn_child() {
let mut cmd = Command::new("some_program");
let _status = unsafe {
cmd.pre_exec(|| {
// Make the child process its own process group leader
if libc::setpgid(0, 0) != 0 {
return Err(std::io::Error::last_os_error());
}
Ok(())
})
}
.status();
}
Meta
rustc --version --verbose
:
rustc 1.85.0-nightly (c94848c04 2024-12-05)
binary: rustc
commit-hash: c94848c046d29f9a80c09aae758e27e418a289f2
commit-date: 2024-12-05
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.5
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A-edition-2024Area: The 2024 editionArea: The 2024 editionA-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.Area: Lints (warnings about flaws in source code) such as unused_mut.C-bugCategory: This is a bug.Category: This is a bug.I-edition-triagedIssue: This issue has been reviewed and triaged by the Edition team.Issue: This issue has been reviewed and triaged by the Edition team.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.