WaffleLapkin
commented
2 years ago Note that this issue is not actually related to #93082, since you can reach the same segfault on stable. Here is a MRE:
use std::io::Write;
fn main() {
let n = 1380;
let open = "impl Trait<Assoc = ".repeat(n);
let close = ">".repeat(n);
let code = format!("
trait Trait {{ type Assoc; }}
impl Trait for () {{ type Assoc = (); }}
fn _f() -> {open}(){close} {{}}
fn main() {{}}
");
std::fs::File::options()
.truncate(true)
.write(true)
.create(true)
.open("./nested_rpit.rs")
.unwrap()
.write(code.as_bytes())
.unwrap();
}(this generates a file nested_rpit.rs that segfaults the compiler)
fredlahde
steffahn
This issue is tightly bound to this PR (93082), which aims to add the ability to return
impl Fn() -> impl Traitfrom a function.I played around with it, and got the idea to test out if there is a limit to how deep we can nest those functions (since the PR also enables
impl Fn() -> impl Fn() -> impl Trait). It quickly noticed a segfault fromrustcand was able to determine the exact depth that causes the crash.Code
For generating test files quickly, I wrote a small code generator:
Once compiled, one can call it like this:
./gen <depth>. Thedepthargument controls the count of-> impl Fn()that is emitted. The following listing is an example withdepthset to 5:If one then tries to compile this with the rustc from the PR at commit 3ed486b37477dde94c87539, the test program compiles successfully.
However, when I set
depthto 560, I get a segfault.Meta
rustc --version --verbose:Error output
I got a backtrace from
gdb:I am not entirely sure, if this is important enough for having it's own issue, since it's so tightly bound to the PR. Feel free to close / move accordingly.