implied bounds from impl header are not used in associated functions/consts

[aliemjay]

The following fails to compile although it shouldn't: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=f7287b6897a385360f7190001b58348d

/// A type with an implied bound `'b: 'a`
struct Ty<'a, 'b>(&'a &'b ());

impl<'a, 'b> Ty<'a, 'b> // <- tait or inherent impl
where
    //'b: 'a, // <- fixed by an explicit bound
{
    fn f() { // <- no `Self` in signature
        Self;
        //~^ ERROR lifetime bound not satisfied
        // Cannot prove WF of `Self` because `'b: 'a` is not known to hold
    }
}

Another repro:

struct Ty<'a, 'b>(&'a &'b ());

impl<'a, 'b> Ty<'a, 'b>{
    fn f() {
        None::<&'a &'b ()>;
        //~^ ERROR lifetime bound not satisfied
    }
}

The first repro regressed in 1.43 while the second one is as old as implied bounds.

@rustbot label A-implied-bounds A-associated-items regression-from-stable-to-stable T-types

Meta

Nightly version: 1.64.0-nightly

(2022-07-01 46b8c23)

Backtrace

<backtrace>

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium

[aliemjay]

The same issue exists for associated consts:

/// A type with an implied bound `'b: 'a`
struct Ty<'a, 'b>(&'a &'b ());

impl<'a, 'b> Ty<'a, 'b> {
    const CONST_1: () = ();
    const CONST_2: () = {
        Self::CONST_1
        //~^ ERROR lifetime may not live long enough
    };
}