Closed
Description
I discovered this bug while tinkering with the frunk crate.
#[derive(PartialEq, Debug)]
struct Cons<H, T: Hlist> {
head: H,
tail: T
}
#[derive(PartialEq, Debug)]
struct Nil;
trait Hlist {}
impl<H, T: Hlist> Hlist for Cons<H, T> {}
impl Hlist for Nil {}
fn main() {
// This part works fine
let x = Cons {head: Some(&0), tail: Nil};
let y = Cons {head: Some(&0), tail: Nil};
assert_eq!(x, y);
// This apparently-equivalent code fails to compile (passes cargo-check but not cargo-build)
assert_eq!(
Cons {head: Some(&0), tail: Nil},
Cons {head: Some(&0), tail: Nil}
);
}This code compiles and runs on stable.
➜ rustup default stable
info: using existing install for 'stable-x86_64-unknown-linux-gnu'
info: default toolchain set to 'stable-x86_64-unknown-linux-gnu'
stable-x86_64-unknown-linux-gnu unchanged - rustc 1.30.0 (da5f414c2 2018-10-24)
➜ cargo build
Finished dev [unoptimized + debuginfo] target(s) in 0.12s
But fails on nightly
➜ rustup default nightly
info: using existing install for 'nightly-x86_64-unknown-linux-gnu'
info: default toolchain set to 'nightly-x86_64-unknown-linux-gnu'
nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.31.0-nightly (cae6efc37 2018-10-27)
➜ cargo build
Compiling typeck v0.1.0
error[E0080]: it is undefined behavior to use this value
--> src/main.rs:15:1
|
15 | / fn main() {
16 | |
17 | | // This part works fine
18 | | let x = Cons {head: Some(&0), tail: Nil};
... |
26 | | );
27 | | }
| |_^ type validation failed: encountered a pointer, but expected something that cannot possibly be outside the (wrapping) range 1..=0
|
= note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
error: aborting due to previous error
For more information about this error, try `rustc --explain E0080`.
error: Could not compile `typeck`.
To learn more, run the command again with --verbose.