Are we async yet?

For async syntax, not yet, but progress is being made!

Although the more ergonomic syntax is not ready yet, asynchronous I/O is already possible in Rust with ecosystem around futures, mio, and tokio.

async syntax and blockers

• async/await syntax not stabilized yet / RFC 2394 / #50547
  Related issues under A-async-await

  • #57640 - Resolve await syntax
  • #57084 - ICE(async_await,futures_api,await_macro,generators): cannot relate bound region: ReLateBound(DebruijnIndex(1), BrAnon(2)) <= '_#1r
  • #57017 - async/await: awaiting inside a match block captures borrow too eagerly
  • #56974 - Cannot define async fn with no_std
  • #56767 - await macro is not in libcore.
  • #56651 - Obscure compiler panic with async/await
  • #56238 - async fn should support multiple lifetimes
  • #55809 - Mixing async functions and &mut leads to overflow evaluating requirement
  • #55324 - async fn doesn't capture lifetimes of type parameters other lifetimes are present
  • #54974 - async fn: 'static lifetime not inferred for Arc trait object
  • #54716 - Unused arguments to async fn are dropped too early
  • #54326 - Mismatched types diagnostic for async fn return type trusts random returns over function signature
  • #53989 - compile async await function error
  • #53714 - async fn inside inherent impl produces generic parse error on 2015 edition
  • #53447 - ICE with --pretty=expanded and async/await
  • #53259 - Missing detection of Send for async fn
  • #51933 - async fn inside fn fails to parse
  • #51751 - async/await error message could be better
  • #50547 - Tracking issue for async/await (RFC 2394)
  • #50458 - Implement DerefAsync and DerefMutAsync as Deref and DerefMut in async context
  • #57036 - async/await: Sending Waker seems to invalidate it
  • #54289 - ICE with async_await + extern crate + invalid import
• std::task and std::future not stabilized yet / RFC 2592
• Pin APIs stabilized in 1.33 [in beta] / RFC 2349 / #49150
• Pin as a method receiver stabilized in 1.33 [in beta] / RFC 2362 / #55786
• 2018 edition stabilized in 1.31 [in stable]
• async as a keyword in 2018 edition stabilized in 1.28 [in stable]
• impl Trait in return position stabilized in 1.26 [in stable] / RFC 1522 / #34511
  Related issues under A-impl-trait

  • #58011 - cargo doc fails to compile existential associated types
  • #57979 - Regression from stable to nightly: nested impl trait is not allowed
  • #57961 - Defining scope of existential type defined by associated type
  • #57807 - Compiler fails to unify existential associated type
  • #57700 - ICE when returning generic abitrary self type in defining function for existential associated type
  • #57201 - Broken MIR impl_trait_in_bindings ICE
  • #57200 - NLL impl_trait_in_bindings ICE
  • #57188 - Existential type captures lifetime that doesn't appear in bounds even though it does appear
  • #56711 - Recursive call passes cargo check but fails with cargo build
  • #56046 - Tracking issue for Captures trait
  • #55997 - Cycle detected when processing existential type
  • #55535 - "does not live long enough" when returning Option<impl trait>
  • #55099 - Incorrect inference of lifetime bound for existential type
  • #55027 - "trait is not implemented" error when returning "impl Trait" hides a more useful error
  • #54771 - Poor Trailing Semicolon Error in -> impl Trait Function
  • #54729 - Wrong type inference for closure with impl Trait inside another type
  • #54600 - impl_trait_in_bindings fails with Option<impl Trait>
  • #54560 - Confusing error message for impl Trait consts/statics that use generics
  • #54385 - impl Trait should be able to capture long-lived associated types even if the trait contains a lifetime
  • #54234 - Incorrect warning: type alias is never used
  • #53984 - impl Trait with associated type equality constraint fails to resolve when constraint contains associated type of non-parameter type
  • #53613 - Lifetimes get replaced with 'static in Self within (return position) impl Trait.
  • #53598 - ICE: Existential type (w/ and w/o NLL)
  • #53457 - non-defining existential type use in defining scope with empty lifetime name
  • #53398 - existential types cannot be defined in terms of themselves at all
  • #53096 - ICE 2018 edition with const fn and existential type
  • #53092 - FullfillmentError ICE with const fn and existential type
  • #53090 - existential type can accept generic bounds that do not specify a trait
  • #52901 - Bad error message with wrong impl trait-parameter on trait implementation
  • #52843 - ICE on unsound usage of existential types
  • #52632 - Existential type can have inconsistent concrete type
  • #52304 - Compiler panic on type inference for impl Generator yielding a reference
  • #51616 - Wrong lifetime is inferred in the argument of closure when given more specific type.
  • #51525 - existential impl trait overlooks "hidden" lifetimes from projections
  • #51069 - impl Trait return value causes an over-restricted lifetime requirement
  • #50823 - impl Trait causes "borrowed value does not live long enough"
  • #50817 - Wrong suggestion for fixing argument-position impl Trait
  • #50652 - Regression in return type error quality with impl trait
  • #49431 - Confusing error message when returning impl Trait with multiple lifetimes
  • #49288 - impl Trait Associated Types Do Not Leak Auto Traits
  • #49287 - Argument-position impl Trait requires a named lifetime
  • #48467 - impl trait error message around 'static is probably confusing
  • #48290 - Confusing Error Message with Impl Trait in E0308
  • #47764 - ICE with impl FnOnce... in argument position. Unexpected panic.
  • #47348 - impl Trait feature is not make code easy
  • #46644 - Compiler incorrectly reports function return type declaration as source of inner type mismatch with conservative_impl_trait
  • #45994 - [impl Trait] Should we allow impl Trait after -> in fn types or parentheses sugar?
  • #44530 - Return type that doesn't satisfy impl Trait messages should point out the reason
  • #42940 - impl-trait return type is bounded by all input type parameters, even when unnecessary
  • #42451 - With impl trait, some variables are not recognised as 'static when used with AsRef.
  • #41407 - type mismatch resolving <Thing as FromStr>::Err == <Thing as FromStr>::Err, with impl trait
  • #37790 - Borrowing issue with impl Trait leads to unergonomic verbosity
  • #37454 - Option + impl Trait = uncompilable code (?)
  • #36375 - impl Trait fails to resolve when returning !
  • #35870 - Using impl trait across crates results in linker error
  • #57933 - The scope of associated existential types
  • #57678 - Existential types: Unused closure environment is part of concrete type
  • #55903 - ICE: "unexpected predicate" when using multiple lifetime parameters in existential type
  • #55608 - ICE on stable / nightly: ReEmpty
  • #54593 - NLL type-checking ICEs on closure recursing on impl Trait-returning enclosing function.
  • #54045 - Regression in #[allow(deprecated)] for impl Trait return type
  • #53791 - existential impl Trait gets seriously confused about lifetimes, "impl T + 'static" does not satisfy static lifetime
  • #53690 - async fn cannot be recursive
  • #53546 - Existential type complains about private type in public interface if concrete type is not pub
  • #53443 - ICE when existential type is exported from one crate and used in another
  • #53087 - ICE with const transmute and existential type
  • #52985 - Existential type ICE
  • #52701 - infinite recursion ICE
  • #52376 - Rustdoc not showing return type but showing return type lifetimes
  • #51282 - impl Trait return value infers 'static lifetime
  • #50950 - Able to use the turbofish syntax with impl trait for methods
  • #50881 - ICE using function pointer to function returning impl Iterator<Item = &&'a str>
  • #50865 - Compiler crashed with cannot create local mono-item
  • #50626 - impl Trait binary operations
  • #50358 - rustdoc panic while documenting impl trait in argument position
  • #49926 - impossible case reached on lifetime inference for impl Trait in return position
  • #49685 - [ICE] librustc_traits/normalize_erasing_regions.rs:46: could not fully normalize ...
  • #49376 - rustc has a stack overflow when using impl Trait of a trait with a generic parameter with a default type of Self
  • #48140 - ICE with conservative_impl_trait
  • #47715 - Compiler crash when using impl Trait to bound associated type parameter
  • #47422 - missing specialization: <encoder::EncodeContext as SpecializedEncoder<rustc::hir::def_id::LocalDefId>>::specialized_encode not overriden
  • #46976 - Rustdoc ICE with argument position impl Trait
  • #46959 - Universal impl trait shows camel case name warning
  • #46685 - ICE combining universal plus existential impl Trait
  • #46541 - 🚀 existential impl Trait allows lifetimes that would not be allowed by abstract type
  • #46504 - Compiler error: returning impl Generator
  • #46476 - ICE when using impl Iterator<Item = &'a Path> + 'a
  • #46470 - [ICE] with conservative_impl_trait and universal_impl_trait
  • #46469 - [ICE] with universal_impl_trait
  • #46468 - [ICE] with underscore_lifetimes
  • #46464 - Nested "impl trait" with lifetimes causing internal compiler error
  • #46456 - librustc_trans_utils/collector.rs:743: Cannot create local trans-item for DefId(11/0:54 ~ stpl[d907]::html[0]::h1[0])
  • #45800 - Link error with incremental and impl trait
  • #45690 - ICE with conservative_impl_trait
  • #44956 - Rustc nightly 2017-09-19 crashes because of impl Iterator with reference Item
  • #44923 - Purely-diverging functions cannot return impl Trait.
  • #44721 - impl Trait in argument position
  • #44686 - Tracking issue for impl trait in const/static/let
  • #44685 - Tracking issue for existential types (RFC 2071)
  • #44437 - None.unwrap() in FnCtxt::instantiate_anon_types
  • #44198 - Impl Trait ICE: escaping regions in predicate
  • #44181 - ICE with generators and impl Trait: "Cannot create local trans-item"
  • #43774 - error: internal compiler error: unexpected panic
  • #43719 - "only named lifetimes allowed in impl Trait" could have a better error message
  • #43718 - ICE: escaping regions in predicate Obligation(...)
  • #43263 - Recursive impl-trait type causes compiler stack overflow
  • #43135 - Using impl Trait with closure local functions across crates results in ICE
  • #43073 - ICE with impl_trait
  • #43021 - compiler panic impl Trait
  • #42399 - ICE in conservative_impl_trait over VecDeque<String> Iterator
  • #42183 - Tracking issue for RFC 1951: Finalize syntax and parameter scoping for impl Trait, while expanding it to arguments
  • #41297 - impl Future used across crate boundaries produces an error
  • #41182 - [ICE] [conservative_impl_trait] escaping regions in predicate
  • #39639 - 'rustc' has overflowed its stack error
  • #38064 - Infinite size checker doesn't see through impl Trait, leading to rustc overflow
  • #37096 - ICE: "Unexpected tail in unsized_info_ty" when using impl Trait

Future extensions

• async iterators or stream unresolved
• better syntax for await expression unresolved

async ecosystem

• tokio - experimental async/await support is provided with the async-await-preview feature flag. / #804