This document is intended to document the current state of Rust’s various unstable features, their current status and what’s required next to be completed.
| Team | Feature | Status | What’s next | Last update |
|---|---|---|---|---|
| compiler + lang | repr(packed) allows invalid unaligned loads | Implemented | Blocked on safe_packed_borrows |
2018-07-14 |
| compiler | Implement likely/unlikely intrinsic (tracking issue for RFC 1131) | Implemented | Blocked on decision to deprecate or redesign | 2018-07-14 |
| compiler | RFC amendment #1384 | Implemented | Blocked on promotion to error | 2018-07-14 |
| compiler | Specialization and lifetime dispatch | Unimplemented | Blocked on specialisation | 2018-07-14 |
| compiler | The “ptx-kernel” ABI | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| compiler | The #[wasm_custom_section] attribute |
Implemented | Blocked decision to change to a more general solution | 2018-07-14 |
| compiler | The #[wasm_import_module] attribute |
Implemented | Blocked on documentation and small design consideration | 2018-07-14 |
| compiler | The msp430-interrupt calling convention/ABI |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| compiler | The thiscall calling convention |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| compiler | The x86-interrupt calling convention |
Implemented | Blocked on LLVM bugs | 2018-07-14 |
| compiler | Trait bounds not checked on specializable associated types | Unimplemented | Blocked on implementation | 2018-07-14 |
| compiler | #[may_dangle], a refined dropck escape hatch (RFC 1327) |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| compiler | arbitrary_self_types |
Implemented | Blocked on RFC | 2018-07-14 |
| compiler | incoherent_fundamental_impls compatibility lint |
Implemented | Hard error PR blocked on second crater run | 2018-07-14 |
| compiler | legacy_directory_ownership future-compatibility warnings |
Implemented | Blocked on making the lint deny by default | 2018-07-14 |
| compiler | parenthesized_params_in_types_and_modules future-compatibility warnings |
Implemented | Blocked on making the lint a hard error | 2018-07-14 |
| compiler | safe_packed_borrows compatibility lint |
Implemented | Blocked on making the lint hard error | 2018-07-14 |
| compiler | underscore_literal_suffix future-compatibility warnings |
Implemented | Blocked on making the lint a hard error | 2018-07-14 |
| compiler | where_clauses_object_safety future compatibility lint |
Implemented | Blocked on making the lint deny by default | 2018-07-14 |
| compiler | 🔬 generic associated types (GAT) | Unimplemented | Blocked on implementation | 2018-07-14 |
| dev-tools + rustdoc | rustdoc --display-warnings |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| dev-tools | Sanitizer support | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| dev-tools | Stabilise -Zsave-analysis |
Unimplemented | Blocked on whether a new approach supersedes this | 2018-07-14 |
| dev-tools | #[link(kind)] connecting libraries on Windows |
Implemented | Blocked on name decision and stabilisation | 2018-07-14 |
| dev-tools | --print target-spec-json |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| dev-tools | -Z profile |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| dev-tools | libtest JSON output | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang + libs | “macro naming and modularisation” (RFC #1561) | Implementation in progress | Blocked on unresolved design decisions | 2018-07-14 |
| lang + libs | RFC 1566: Procedural macros | Implementation in progress | Blocked on macros 1.2 stabilisation | 2018-07-14 |
| lang + libs | DST coercions (coerce_unsized, unsize) | Unimplemented | Blocked on creation of custom DST RFC | 2018-07-14 |
| lang + libs | Fn traits (unboxed_closures feature) |
Implemented | Blocked on unresolved design decisions | 2018-07-14 |
| lang + libs | concat_idents |
Implemented | Blocked on macro improvements | 2018-07-14 |
| lang + libs | std::raw |
Unimplemented | Blocked on deprecation implementation | 2018-07-14 |
| lang | ‘Allow Self to appear in the where clause of trait impls’ |
Implemented | Blocked on #35237 | 2018-07-14 |
| lang | 128-bit integer support (RFC 1504) | Implementation in progress | Blocked on enums with 128 discriminant | 2018-07-14 |
| lang | Allocator traits and std::heap | Implementation in progress | Blocked on audit and design decisions | 2018-07-14 |
| lang | Allow all literals in attributes (Tracking Issue for RFC #1559) | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | Allowing overlapping implementations for marker trait. | Implemented | Blocked on documentation | 2018-07-14 |
| lang | Exclusive range patterns | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | Exhaustive integer patterns tracking issue | Implementation in progress | Blocked implementation being merged | 2018-07-14 |
| lang | Naked fns (RFC #1201) | Implemented | Blocked on design feedback and the inline assembly feature. | 2018-07-14 |
| lang | Nonparametric dropck (tracking issue for RFC 1238) | Implemented | Blocked on #[may_dangle] and dropck_parametricity |
2018-07-14 |
| lang | Opt-in built-in bounds traits RFC tracker (optin_builtin_traits) | Implementation in progress | Blocked on conditional negative implements implementation | 2018-07-14 |
| lang | Option::xor | Implemented | Blocked on decision to stable | 2018-07-14 |
| lang | Patterns in functions without body | Implemented | Blocked on making lint deny by default | 2018-07-14 |
| lang | Promoting ! to a type (RFC 1216) |
Implementation in progress | Blocked on decision around coercion | 2018-07-14 |
| lang | RFC #495 (features slice_patterns and advanced_slice_patterns) |
Implemented | Blocked on NLL | 2018-07-14 |
| lang | RFC 1872: exhaustive_patterns |
Implemented | Blocked on the never type | 2018-07-14 |
| lang | RFC 554: pattern_parentheses |
Implemented | Blocked on stabilisation PR | 2018-07-14 |
| lang | The #[used] attribute |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | The lifetime specifier for macro_rules! |
Implemented | Waiting on 1.28.0 stable release | 2018-07-14 |
| lang | Tracking Issue for RFC 213: Default Type Parameter Fallback | Implemented | Blocked on unresolved design decisions | 2018-07-14 |
| lang | Tracking issue: declarative macros 2.0 | Implementation in progress | Blocked on macro 2.0 hygiene RFC | 2018-07-14 |
| lang | Trait aliases | Unimplemented | Blocked on implementation | 2018-07-14 |
| lang | Tweaks to object safety (RFC 2027) | Unimplemented | Blocked on implementation | 2018-07-14 |
| lang | Type ascription (tracking issue for RFC 803) | Implementation in progress | Blocked on decision to deprecate or redesign | 2018-07-14 |
| lang | Unsized tuple coercion | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | Untagged unions (RFC 1444) | Unimplemented | Blocked on unresolved questions. | 2018-07-14 |
| lang | #[link_args] |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | #[repr(packed = "N")] (RFC 1399) |
Unimplemented | Blocked on unresolved questions | 2018-07-14 |
| lang | #[thread_local] |
Implemented | Blocked on Unsoundness with generators | 2018-07-14 |
| lang | :vis macro matcher |
Implemented | Blocked on crate becoming a keyword |
2018-07-14 |
| lang | ? macro repetition |
Implemented | Blocked on decision around edition dependent behaviour | 2018-07-14 |
| lang | ? operator and catch expressions (RFC 243, question_mark) |
Implemented | Blocked on reservation of try operator. |
2018-07-14 |
| lang | asm (inline assembly) |
Implemented | Blocked on unclear stability guarantees | 2018-07-14 |
| lang | box_patterns |
Implemented | Blocked on box_syntax feature |
2018-07-14 |
| lang | cfg_target_vendor |
Implemented | Blocked on decision for stabilisation | 2018-07-14 |
| lang | custom_attribute & rustc_attrs |
Unimplemented | Blocked on decision for deprecation or stabilisation | 2018-07-14 |
| lang | custom_derive |
Deprecated | Blocked on rocket for removal | 2018-07-14 |
| lang | fundamental feature |
Unimplemented | Blocked on further dicussion | 2018-07-14 |
| lang | illegal_floating_point_literal_pattern compatibility lint |
Implemented | Blocked on making the lint deny by default | 2018-07-14 |
| lang | impl Trait (RFC 1522, RFC 1951, RFC 2071) |
Implementation in progress | Blocked elision, error messages, and abstract type |
2018-07-14 |
| lang | invalid_type_param_default compatibility lint |
Implemented | Blocked on making the lint a hard error | 2018-07-14 |
| lang | legacy_constructor_visibility compatibility lint |
Implemented | Blocked on making the lint a hard error | 2018-07-14 |
| lang | link_llvm_intrinsics |
Implemented | Apparently permanently unstable | 2018-07-14 |
| lang | literal fragment specifier (RFC 1576) |
Implemented | Waiting on 1.28.0 stable release | 2018-07-14 |
| lang | log_syntax, trace_macros |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | main feature |
Implemented | Blocked on unclear direction | 2018-07-14 |
| lang | no_core stabilization |
Implemented | Blocked on lang items | 2018-07-14 |
| lang | on_unimplemented feature |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | plugin, plugin_registrar features |
Implemented | Blocked on macros 2.0 | 2018-07-14 |
| lang | private_in_public compatibility lint. |
Implemented | Blocked on PR to make lint deny by default | 2018-07-14 |
| lang | quote feature |
Implemented | Blocked on deprecation by macros 2.0 | 2018-07-14 |
| lang | resolve_trait_on_defaulted_unit compatibility lint |
Implemented | Blocked on making the lint a hard error | 2018-07-14 |
| lang | safe_extern_statics compatibility lint |
Implemented | Blocked on making the lint a hard error | 2018-07-14 |
| lang | use $crate; compatibility warning |
Implemented | Blocked on making the lint deny by default | 2018-07-14 |
| lang | {Range, RangeFrom, RangeTo}::contains |
Implemented | Blocked on unresolved questions | 2018-07-14 |
| lang | const fn tracking issue (RFC 911) | Implemented | Blocked on unresolved design decisions | 2018-07-14 |
| lang | constant prop not causing add’l errors (RFC #1229) | Unimplemented | Currently unclear on what is required next | 2018-07-14 |
| lang | non-ASCII identifiers (feature “non_ascii_idents”) | Implemented | Blocked on allow non-ASCII RFC decision | 2018-07-14 |
| lang | stmt_expr_attributes: Add attributes to expressions, etc. | Implemented | Blocked on stabilisation of attributes on expressions and blocks | 2018-07-14 |
| lang | the linkage feature |
Implemented | Blocked on #18804 | 2018-07-14 |
| lang | the start feature |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| lang | associated_type_defaults |
Unimplemented | Blocked on decision on deprecation or semantic change | 2018-07-14 |
| libes | Specialization (RFC 1210) | Implemented | Blocked on restrictions of lifetime dispatch | 2018-07-14 |
| libs | API convention for blocking-, timeout-, and/or deadline-related functions | Unimplemented | Blocked on FCP | 2018-07-14 |
| libs | Add is_empty function to ExactSizeIterator |
Unimplemented | Blocked on unresolved design decisions | 2018-07-14 |
| libs | Adding more atomic integer types | Implementation in progress | Blocked on atomic 128 bit integers. |
2018-07-14 |
| libs | Allow a HashMap and BTreeMap entry to be replaced. |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| libs | Cell::update | Implemented | Blocked on unresolved questions | 2018-07-14 |
| libs | Custom allocators in standard collections | Implementation in progress | Blocked on #47043 and #50882 | 2018-07-14 |
| libs | FixedSizeArray trait | Implemented | Blocked on const generics | 2018-07-14 |
| libs | FnBox() | Unimplemented | Blocked on issues with the borrow checker | 2018-07-14 |
| libs | IP constructors | Implementation in progress | Blocked on moving the implementation to use associated consts | 2018-07-14 |
| libs | Integer methods for Wrapping | Implementation in progress | Some methods are still missing implementations. | 2018-07-14 |
| libs | Ipv{4,6}Addr convenience methods | Implementation in progress | Blocked on #51832 | 2018-07-14 |
| libs | Path/PathBuf normalization methods | Unimplemented | Blocked on implementation | 2018-07-14 |
| libs | Pluggable panic implementations (RFC 1513) | Unimplemented | Blocked on unresolved design decisions | 2018-07-14 |
| libs | RFC 2045: improving #[target_feature] |
Implemented | Blocked on documentation and stabilisation | 2018-07-14 |
| libs | Reversing the bit pattern in an integer | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| libs | SIMD support | Implementation in progress | Blocked on implementation | 2018-07-14 |
| libs | Tracking Issue: Duration::{as_nanos, as_micros, as_millis} | Implemented | Blocked on decision to stable | 2018-07-14 |
| libs | TrustedLen (trusted_len) |
Implemented | Blocked on specialisation | 2018-07-14 |
| libs | TryFrom/TryInto traits | Implemented | Blocked on the !/never type |
2018-07-14 |
| libs | UnicodeVersion and UNICODE_VERSION | Implemented | Blocked on concerns on whether updating const values is a breaking change | 2018-07-14 |
| libs | Vec::remove_item | Implemented | Blocked on unresolved concerns | 2018-07-14 |
| libs | Vec::resize_default | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| libs | #[bench] and benchmarking support |
Implemented | Blocked on black_box RFC |
2018-07-14 |
| libs | Box::into_raw_non_null |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| libs | Read::initializer |
Implemented | Blocked on design decisions | 2018-07-14 |
| libs | Result<Option> and Option<Result> Conversion |
Implemented | Blocked on unresolved questions | 2018-07-14 |
| libs | ToOwned::clone_into |
Implemented | Blocked on concerns | 2018-07-14 |
| libs | Vec::drain_filter and LinkedList::drain_filter |
Implemented | Blocked on design decisions | 2018-07-14 |
| libs | exact_chunks,exact_chunks_mut |
Implemented | Blocked on unresolved questions | 2018-07-14 |
| libs | ops::Try |
Implemented? | Unclear on what is required next | 2018-07-14 |
| libs | ptr::offset_to |
Deprecated | Blocked on removal | 2018-07-14 |
| libs | slice_concat_ext |
Implemented | Blocked on documentation and decision to stabilise | 2018-07-14 |
| libs | std::io::{set_panic, set_print} |
Implemented | Blocked on decision to stabilise | 2018-07-14 |
| libs | step_trait stabilization |
Implementation in progress | Blocked on replacement methods and TrustedLen |
2018-07-14 |
| libs | sync::Once poisoning |
Implemented | Blocked on inactivity | 2018-07-14 |
| libs | channel selection | Implemented | Blocked on decision to stabilise the select! macro |
2018-07-14 |
| libs | crates that are compiler dependencies | Unimplemented | Blocked on unclear direction | 2018-07-14 |
| libs | extra linked list methods | Implemented | Blocked on decision to stabilise | 2018-07-14 |
| libs | location of facade crates | Implementation in progress | Blocked on RFC 2480 | 2018-07-14 |
| libs | str escaping | Implemented | Blocked on stabilisation PR | 2018-07-14 |
| libs | string patterns | Unimplemented | Blocked on RFC 2295 | 2018-07-14 |
| libs | type_id | Implemented | Blocked on FCP confusion | 2018-07-14 |
| libs | write_all_at/read_exact_at convenience methods | Implemented | Blocked on decision to stabilise | 2018-07-14 |