This is a tracking issue for trait aliases (rust-lang/rfcs#1733).

TODO:

• Implement: tracking issue
• Bringing a trait alias into scope doesn't allow calling methods from its component traits #56485 — Bringing a trait alias into scope doesn't allow calling methods from its component traits (done in resolve: collect trait aliases along with traits #59166)
• ICE with trait aliases and use items #56488 — ICE with trait aliases and use items
• Nightly Type Alias Compiler panic unexpected definition: TraitAlias #57023 — Nightly Type Alias Compiler panic unexpected definition: TraitAlias
• INCOHERENT_AUTO_TRAIT_OBJECTS future-compatibility warning #57059 — INCOHERENT_AUTO_TRAIT_OBJECTS future-compatibility warning (superseded by add coherence future-compat warnings for marker-only trait objects #56481)
• Document
• Stabilize

Unresolved questions:

• Are bounds on other input types than the receiver enforced or implied?
• Should we keep the current behaviour of "shallow-banning" ?Sized bounds in trait objects, ban them "deeply" (through trait alias expansion), or permit them everywhere with no effect?
• Insufficient flexibility
• Inconvenient syntax
• Misleading naming
• Which of constraint/bound/type aliases are desirable