Tracking issue for member constraints in region inference

[nikomatsakis]

Member constraints

#61775 introduced "member constraints" as part of stabilizing async functions. These extend region inference to accommodate impl Trait return types that contain multiple unrelated lifetimes (e.g., impl Trait<'a, 'b> where neither 'a: 'b nor 'b: 'a). We decided to introduce a feature gate for other cases until we have time to gain more experience.

Learn more

The working of these constraints is described in the rustc-guide -- as of this writing, however, the PR has not yet landed.

Current status

• Implemented (generalize impl trait to permit multiple lifetime bounds #61775)
• Described in rustc-guide (Region inference member constraints rustc-dev-guide#344)
• Stabilized

Related issues

• Impl trait (Tracking issue for impl Trait (RFC 1522, RFC 1951, RFC 2071) #34511)
• Uncertain interaction with impl trait in bindings (impl_trait_in_bindings and pick-constraint region bounds #61773)

[runiq]

Triage: The first two boxes can be checked and the rustc-guide PR has landed, so this:

as of this writing, however, the PR has not yet landed.

is inaccurate now, which is a good thing. :)

[nikomatsakis]

I am beginning work towards stabilizing this.

@rustbot claim