RFC 1214 warning in librustc_mir/repr.rs

[apasel422]

Building nightly yields

../rust/src/librustc_mir/repr.rs:404:5: 404:38 warning: the parameter type `V` may not live long enough [E0309]
../rust/src/librustc_mir/repr.rs:404     pub elem: ProjectionElem<'tcx, V>,
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../rust/src/librustc_mir/repr.rs:401:24: 401:33 note: in this expansion of #[derive_PartialEq] (defined in ../rust/src/librustc_mir/repr.rs)
../rust/src/librustc_mir/repr.rs:404:5: 404:38 help: run `rustc --explain E0309` to see a detailed explanation
../rust/src/librustc_mir/repr.rs:404:5: 404:38 help: consider adding an explicit lifetime bound `V: 'tcx`...
../rust/src/librustc_mir/repr.rs:404:5: 404:38 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details.
../rust/src/librustc_mir/repr.rs:404     pub elem: ProjectionElem<'tcx, V>,
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../rust/src/librustc_mir/repr.rs:401:24: 401:33 note: in this expansion of #[derive_PartialEq] (defined in ../rust/src/librustc_mir/repr.rs)
../rust/src/librustc_mir/repr.rs:404:5: 404:38 note: ...so that the reference type `&repr::ProjectionElem<'_, V>` does not outlive the data it points at
../rust/src/librustc_mir/repr.rs:404     pub elem: ProjectionElem<'tcx, V>,
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../rust/src/librustc_mir/repr.rs:401:24: 401:33 note: in this expansion of #[derive_PartialEq] (defined in ../rust/src/librustc_mir/repr.rs)
../rust/src/librustc_mir/repr.rs:404:5: 404:38 warning: the parameter type `V` may not live long enough [E0309]
../rust/src/librustc_mir/repr.rs:404     pub elem: ProjectionElem<'tcx, V>,
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../rust/src/librustc_mir/repr.rs:401:24: 401:33 note: in this expansion of #[derive_PartialEq] (defined in ../rust/src/librustc_mir/repr.rs)
../rust/src/librustc_mir/repr.rs:404:5: 404:38 help: run `rustc --explain E0309` to see a detailed explanation
../rust/src/librustc_mir/repr.rs:404:5: 404:38 help: consider adding an explicit lifetime bound `V: 'tcx`...
../rust/src/librustc_mir/repr.rs:404:5: 404:38 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details.
../rust/src/librustc_mir/repr.rs:404     pub elem: ProjectionElem<'tcx, V>,
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../rust/src/librustc_mir/repr.rs:401:24: 401:33 note: in this expansion of #[derive_PartialEq] (defined in ../rust/src/librustc_mir/repr.rs)
../rust/src/librustc_mir/repr.rs:404:5: 404:38 note: ...so that the reference type `&repr::ProjectionElem<'_, V>` does not outlive the data it points at
../rust/src/librustc_mir/repr.rs:404     pub elem: ProjectionElem<'tcx, V>,
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../rust/src/librustc_mir/repr.rs:401:24: 401:33 note: in this expansion of #[derive_PartialEq] (defined in ../rust/src/librustc_mir/repr.rs)

[apasel422]

A reduction of the code in question is available here: https://play.rust-lang.org/?gist=9893feaa919468e9f534&version=nightly

CC @nikomatsakis @arielb1.

[arielb1]

Further reduced:

pub struct Xyz<'a, V> {
    v: (V, &'a u32),
}

fn eq<'a, 's, 't, V>(this: &'s Xyz<'a, V>, other: &'t Xyz<'a, V>) -> bool
        where V: PartialEq {
    this.v == other.v
}

fn main() {}

[arielb1]

It looks like the borrow of this.v is not constrained and is therefore inferred to 'a.