Double-indirection with Cow causes inconsistent behavior of the borrow checker #43058
Description
UPDATE: This needs a test! Mentoring instructions can be found here.
While working on some code using std::borrow::Cow I encountered some strange behavior. Here is a simplified version of the code I was using:
use std::borrow::Cow;
#[derive(Clone, Debug)]
struct S<'a> {
name: Cow<'a, str>
}
#[derive(Clone, Debug)]
struct T<'a> {
s: Cow<'a, [S<'a>]>
}
fn main() {
let s1 = [S { name: Cow::Borrowed("Test1") }, S { name: Cow::Borrowed("Test2") }];
let b1 = T { s: Cow::Borrowed(&s1) };
let s2 = [S { name: Cow::Borrowed("Test3") }, S { name: Cow::Borrowed("Test4") }];
let b2 = T { s: Cow::Borrowed(&s2) };
let mut v = Vec::new();
v.push(b1);
v.push(b2);
println!("{:?}", v);
}
This fails with
error[E0597]:
s2does not live long enough
Removing b1,s1 or b2,s2 from the code fixes the error. However, since the very same pattern isused for both variable pairs it seems to be inconsistent behavior of the borrow checker.
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Versions checked:
rustc 1.18.0 (03fc9d6 2017-06-06)
binary: rustc
commit-hash: 03fc9d6
commit-date: 2017-06-06
host: x86_64-pc-windows-gnu
release: 1.18.0
LLVM version: 3.9
rustc 1.19.0-beta.2 (a175ee5 2017-06-15)
rustc 1.20.0-nightly (734c836 2017-07-03)
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Area: Non-lexical lifetimes (NLL)Area: The borrow checkerArea: Type systemCategory: This is a bug.Call for participation: This issue has a mentor. Use #t-compiler/help on Zulip for discussion.Call for participation: An issue has been fixed and does not reproduce, but no test has been added.Low priorityBugs fixed, but only when NLL is enabled.