Rust: cannot infer lifetime for type_id

[Dylan-DPC]

from a crater run:

Error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
[INFO] [stderr]    --> /opt/crater/cargo-home/registry/src/github.com-1ecc6299db9ec823/data-buffer-0.4.3/src/lib.rs:214:38
[INFO] [stderr]     |
[INFO] [stderr] 214 |         if TypeId::of::<T>() != self.type_id() { None } else { Some(self) }
[INFO] [stderr]     |                                      ^^^^^^^
[INFO] [stderr]     |
[INFO] [stderr] note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 213:5...
[INFO] [stderr]    --> /opt/crater/cargo-home/registry/src/github.com-1ecc6299db9ec823/data-buffer-0.4.3/src/lib.rs:213:5
[INFO] [stderr]     |
[INFO] [stderr] 213 | /     pub fn check_mut<T: Any>(&mut self) -> Option<&mut Self> {
[INFO] [stderr] 214 | |         if TypeId::of::<T>() != self.type_id() { None } else { Some(self) }
[INFO] [stderr] 215 | |     }
[INFO] [stderr]     | |_____^
[INFO] [stderr]     = note: ...so that the types are compatible:
[INFO] [stderr]             expected &&mut DataBuffer
[INFO] [stderr]                found &&mut DataBuffer
[INFO] [stderr]     = note: but, the lifetime must be valid for the static lifetime...
[INFO] [stderr] note: ...so that the type `&mut DataBuffer` will meet its required lifetime bounds
[INFO] [stderr]    --> /opt/crater/cargo-home/registry/src/github.com-1ecc6299db9ec823/data-buffer-0.4.3/src/lib.rs:214:38
[INFO] [stderr]     |
[INFO] [stderr] 214 |         if TypeId::of::<T>() != self.type_id() { None } else { Some(self) }

crate affected: data-buffer
Owner: @elrnv
Log:
https://crater-reports.s3.amazonaws.com/beta-1.34-1/beta-2019-02-27/reg/data-buffer-0.4.3/log.txt

[Dylan-DPC]

cc @rust-lang/libs

[elrnv]

Thanks for reporting! This should be fixed in data-buffer 0.5, which I published just an hour ago or so. Since I used type_id in the api, it was a breaking change.

[alexcrichton]

Reduced I believe this looks like:

use std::any::Any;

struct A;

impl A {
    pub fn by_mut(&mut self) {
        self.type_id();
    }

    fn type_id(&self) {
        println!("hi");
    }
}

fn main() {
    A.by_mut();
}

Today this compiles on stable but it fails to compile on beta.

The cause of this is almost certainly https://github.com/rust-lang/rust/pull/57834/files where the type_id method was renamed during stabilization. Historically this sort of breakage, while definitely unfortunate, is acceptable under our current semver and compatibility policy. Barring a large amount of practical breakage in the ecosystem we're unlikely to revert the change.

Sorry again @elrnv for the regression, but good to hear that this is fixed already as well!

[jonas-schievink]

This seems to be resolved, so I'll close this. Feel free to reopen if that's wrong.