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Implement #[async_send] attribute for async fns #107056

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Implement #[async_send] attribute for async fns #107056

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4a56673
Implement #[async_send] attribute for async fns
eholk Jan 19, 2023
06851de
Add test for #[async_send] functionality
eholk Jan 19, 2023
cabd064
Add a test the ensure the #[async_send] attribute is feature gated
eholk Jan 19, 2023
6ca9bf2
Look in the right attributes for async_send
eholk Jan 19, 2023
01816de
Fix RustDoc
eholk Jan 19, 2023
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28 changes: 27 additions & 1 deletion compiler/rustc_ast_lowering/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1801,6 +1801,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);

let fn_def_id = self.local_def_id(fn_node_id);
let fn_local_id = self.lower_node_id(fn_node_id).local_id;

let opaque_ty_def_id =
self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait, opaque_ty_span);
Expand Down Expand Up @@ -1967,6 +1968,31 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
));
debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);

let is_async_send = this.tcx.features().async_fn_in_trait
&& (true
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is this needed?

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The true definitely isn't! (Sorry, that was left over from by debugging attempts).

The async_fn_in_trait check is probably not needed either since you can't even type this attribute without it. I'll try and remove it.

|| this.attrs.get(&fn_local_id).map_or(false, |attrs| {
attrs.into_iter().any(|attr| attr.has_name(sym::async_send))
}));

// Add Send bound if `#[async_send]` attribute is present
let bounds = if is_async_send {
let send_bound = hir::GenericBound::LangItemTrait(
hir::LangItem::Send,
this.lower_span(span),
this.next_id(),
this.arena.alloc(hir::GenericArgs {
args: &[],
bindings: &[],
parenthesized: false,
span_ext: DUMMY_SP,
}),
);

arena_vec![this; future_bound, send_bound]
} else {
arena_vec![this; future_bound]
};

let opaque_ty_item = hir::OpaqueTy {
generics: this.arena.alloc(hir::Generics {
params: generic_params,
Expand All @@ -1975,7 +2001,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
where_clause_span: this.lower_span(span),
span: this.lower_span(span),
}),
bounds: arena_vec![this; future_bound],
bounds,
origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
in_trait,
};
Expand Down
4 changes: 4 additions & 0 deletions compiler/rustc_feature/src/builtin_attrs.rs
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Expand Up @@ -490,6 +490,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
// RFC 2397
gated!(do_not_recommend, Normal, template!(Word), WarnFollowing, experimental!(do_not_recommend)),

gated!(async_send, Normal, template!(Word), ErrorFollowing, async_fn_in_trait,
"`async_send` is a temporary placeholder for marking async methods as returning a future \
that is also Send and may be removed or renamed in the future."),

// ==========================================================================
// Internal attributes: Stability, deprecation, and unsafe:
// ==========================================================================
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_hir/src/lang_items.rs
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Expand Up @@ -216,6 +216,7 @@ language_item_table! {
FnOnceOutput, sym::fn_once_output, fn_once_output, Target::AssocTy, GenericRequirement::None;

Future, sym::future_trait, future_trait, Target::Trait, GenericRequirement::Exact(0);
Send, sym::send, send_trait, Target::Trait, GenericRequirement::Exact(0);
GeneratorState, sym::generator_state, gen_state, Target::Enum, GenericRequirement::None;
Generator, sym::generator, gen_trait, Target::Trait, GenericRequirement::Minimum(1);
Unpin, sym::unpin, unpin_trait, Target::Trait, GenericRequirement::None;
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_span/src/symbol.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -393,6 +393,7 @@ symbols! {
async_await,
async_closure,
async_fn_in_trait,
async_send,
atomic,
atomic_mod,
atomics,
Expand Down Expand Up @@ -1297,6 +1298,7 @@ symbols! {
self_in_typedefs,
self_struct_ctor,
semitransparent,
send,
shadow_call_stack,
shl,
shl_assign,
Expand Down
1 change: 1 addition & 0 deletions library/core/src/marker.rs
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Expand Up @@ -31,6 +31,7 @@ use crate::hash::Hasher;
/// [ub]: ../../reference/behavior-considered-undefined.html
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "Send")]
#[cfg_attr(not(bootstrap), lang = "send")]
#[rustc_on_unimplemented(
message = "`{Self}` cannot be sent between threads safely",
label = "`{Self}` cannot be sent between threads safely"
Expand Down