# Backlog Bonanza 2021-12-08 [GitHub query](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AC-tracking-issue+label%3AT-lang) ## omg what are we doing * Take things that have been unstable for a while and "disposition them". * Goal: Everything that is nightly only has one or more of the following labels, indicating the blocker(s) to stabilizing it: * S-tracking-ready-to-stabilize: Needs a stabilization PR (good to go :train:) * S-tracking-needs-to-bake: Needs time to bake (set a date? other criteria?) * S-tracking-impl-incomplete: Not code complete or blocking bugs * S-tracking-unimplemented: Implementation not begun * S-tracking-design-concerns: Blocking design concerns * This might be "doesn't quite seem to deliver value we hoped for" or "something doesn't feel right" * S-tracking-perma-unstable * Internal implementation detail of rustc, stdlib * S-tracking-needs-investigation Attendance: Josh, Felix, Mark --- # Implement likely/unlikely intrinsic (tracking issue for RFC 1131) #26179 Tracking issue: https://github.com/rust-lang/rust/issues/26179 * we previously discussed this as "seemed fine", if libs wants this as a function * libs kicked this over to lang, preferring an attribute * unclear whether these work today * perma-unstable / as LLVM intrinsics # Tracking issue for the linkage feature #29603 Tracking issue: https://github.com/rust-lang/rust/issues/29603 * `#[weak]` probably wants some other word in there to be more google-able * The full surface area tracked by linkage (everything supported by LLVM) is something we'd not fully stabilize * And attributes may be somewhat composable * `#[linkage(weak, odr)]` * perma-unstable for now, open to stabilizing parts with concrete proposals (file a T-lang MCP) # Tracking issue for Fn traits (unboxed_closures feature) #29625 Tracking issue: https://github.com/rust-lang/rust/issues/29625 * https://doc.rust-lang.org/beta/unstable-book/language-features/unboxed-closures.html * https://doc.rust-lang.org/beta/unstable-book/library-features/fn-traits.html `#[unstable(feature = "fn_traits", issue = "29625")]` * Likely want a solution in this space * But, this solution may not be the solution we want * May want "proper" variadic generics over tuples ```rust= error[E0658]: the precise format of `Fn`-family traits' type parameters is subject to change --> src/lib.rs:1:18 | 1 | fn foo() -> impl std::ops::Fn<(i32)> {} | ^^^^^^^^^^^^^^^^^^^ help: use parenthetical notation instead: `Fn(i32) -> ()` ``` # Tracking issue for the start feature #29633 Tracking issue: https://github.com/rust-lang/rust/issues/29633 * no_std + `#[start]` may be feasible * surface area commitment: what works without the std entry point? * probably achievable today with some hacks today (linker script, etc) * design work/thinking that needs to happen before stabilization * e.g., whether the signature is cross-platform compatible, or what is needed around that # Tracking issue for fundamental feature #29635 Tracking issue: https://github.com/rust-lang/rust/issues/29635 * Discussion about what `#[fundamental]` means * on structs, and on traits * What do people actually want to use this for? * Design concerns: * non-std libraries with fundamental types cannot impl new traits, due to possible breakage * Potentially perma-unstable, but needs summary of what this feature means and the use cases for it are (in std and outside) # Tracking issue for no_core stabilization #29639 Tracking issue: https://github.com/rust-lang/rust/issues/29639 * Possible use cases: * 30 byte large binaries * macro-only crates, as core deps * we may be able to improve core itself such that LTO, etc. are good enough that no_core is no longer necessary * IOW, "core brings in stuff for no good reason" is a 'bug', and this may not be the right solution # Tracking issue for box_patterns feature #29641 Tracking issue: https://github.com/rust-lang/rust/issues/29641 * perma-unstable in favor of deref patterns * forward progress in other syntaxes/features, not in this particular feature # Tracking issue for RFC 2532, "Associated type defaults" #29661 Tracking issue: https://github.com/rust-lang/rust/issues/29661 * needs summary -- is the checklist right? * Mark to post comment