Danilo Krummrich 1b56056294 rust: types: introduce ForLt base trait for CovariantForLt ...

Add a new ForLt trait as a base for CovariantForLt:

  - ForLt (non-unsafe): represents a type generic over a lifetime, with
    no covariance guarantee.

  - CovariantForLt (unsafe): becomes a subtrait of ForLt that
    additionally proves the type is covariant over its lifetime
    parameter, providing a safe cast_ref() method.

This split allows non-covariant types (e.g. types behind a Mutex) to
implement ForLt and participate in DevresLt / registration data patterns
that use HRTB closures for sound access, without requiring a covariance
proof that would fail to compile.

Both macros share the UnsafeForLtImpl helper type, distinguished by
a const generic N: ForLt! emits N = 0 (no covariance proof),
CovariantForLt! emits N = 1 (with compile-time covariance proof).

Reviewed-by: Gary Guo <[email protected]>
Acked-by: Miguel Ojeda <[email protected]>
Link: https://patch.msgid.link/[email protected]
[ Merge ForLt pub use, inline resolve_hrt/ty_static, add intra-doc
  links. - Danilo ]
Signed-off-by: Danilo Krummrich <[email protected]>

2026-07-11 19:42:03 +02:00

..

for_lt.rs

rust: types: introduce ForLt base trait for CovariantForLt

2026-07-11 19:42:03 +02:00