From 04fa9b1b3f947fa66bb3e92702e134c72af9486f Mon Sep 17 00:00:00 2001 From: David Wood Date: Wed, 25 Sep 2019 13:58:41 +0100 Subject: [PATCH] async/await: improve obligation errors This commit improves obligation errors for async/await: ``` note: future does not implement `std::marker::Send` because this value is used across an await --> $DIR/issue-64130-non-send-future-diags.rs:15:5 | LL | let g = x.lock().unwrap(); | - has type `std::sync::MutexGuard<'_, u32>` LL | baz().await; | ^^^^^^^^^^^ await occurs here, with `g` maybe used later LL | } | - `g` is later dropped here ``` Signed-off-by: David Wood --- src/librustc/traits/error_reporting.rs | 177 ++++++++++++++++-- src/librustc/ty/context.rs | 35 ++++ src/librustc/ty/mod.rs | 2 +- .../check/generator_interior.rs | 15 +- src/librustc_typeck/check/writeback.rs | 7 + src/libstd/future.rs | 1 + .../ui/async-await/async-fn-nonsend.stderr | 24 +-- .../issue-64130-non-send-future-diags.rs | 25 +++ .../issue-64130-non-send-future-diags.stderr | 23 +++ 9 files changed, 281 insertions(+), 28 deletions(-) create mode 100644 src/test/ui/async-await/issue-64130-non-send-future-diags.rs create mode 100644 src/test/ui/async-await/issue-64130-non-send-future-diags.stderr diff --git a/src/librustc/traits/error_reporting.rs b/src/librustc/traits/error_reporting.rs index c2d531793372a..05b561a1ed55a 100644 --- a/src/librustc/traits/error_reporting.rs +++ b/src/librustc/traits/error_reporting.rs @@ -24,7 +24,7 @@ use crate::hir::def_id::DefId; use crate::infer::{self, InferCtxt}; use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; use crate::session::DiagnosticMessageId; -use crate::ty::{self, AdtKind, ToPredicate, ToPolyTraitRef, Ty, TyCtxt, TypeFoldable}; +use crate::ty::{self, AdtKind, DefIdTree, ToPredicate, ToPolyTraitRef, Ty, TyCtxt, TypeFoldable}; use crate::ty::GenericParamDefKind; use crate::ty::error::ExpectedFound; use crate::ty::fast_reject; @@ -37,7 +37,7 @@ use errors::{Applicability, DiagnosticBuilder, pluralise}; use std::fmt; use syntax::ast; use syntax::symbol::{sym, kw}; -use syntax_pos::{DUMMY_SP, Span, ExpnKind}; +use syntax_pos::{DUMMY_SP, Span, ExpnKind, MultiSpan}; impl<'a, 'tcx> InferCtxt<'a, 'tcx> { pub fn report_fulfillment_errors( @@ -550,7 +550,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> { self.suggest_new_overflow_limit(&mut err); } - self.note_obligation_cause(&mut err, obligation); + self.note_obligation_cause_code(&mut err, &obligation.predicate, &obligation.cause.code, + &mut vec![]); err.emit(); self.tcx.sess.abort_if_errors(); @@ -940,7 +941,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> { bug!("overflow should be handled before the `report_selection_error` path"); } }; + self.note_obligation_cause(&mut err, obligation); + err.emit(); } @@ -1604,15 +1607,165 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> { }) } - fn note_obligation_cause(&self, - err: &mut DiagnosticBuilder<'_>, - obligation: &Obligation<'tcx, T>) - where T: fmt::Display - { - self.note_obligation_cause_code(err, - &obligation.predicate, - &obligation.cause.code, - &mut vec![]); + fn note_obligation_cause( + &self, + err: &mut DiagnosticBuilder<'_>, + obligation: &PredicateObligation<'tcx>, + ) { + // First, attempt to add note to this error with an async-await-specific + // message, and fall back to regular note otherwise. + if !self.note_obligation_cause_for_async_await(err, obligation) { + self.note_obligation_cause_code(err, &obligation.predicate, &obligation.cause.code, + &mut vec![]); + } + } + + /// Adds an async-await specific note to the diagnostic: + /// + /// ```ignore (diagnostic) + /// note: future does not implement `std::marker::Send` because this value is used across an + /// await + /// --> $DIR/issue-64130-non-send-future-diags.rs:15:5 + /// | + /// LL | let g = x.lock().unwrap(); + /// | - has type `std::sync::MutexGuard<'_, u32>` + /// LL | baz().await; + /// | ^^^^^^^^^^^ await occurs here, with `g` maybe used later + /// LL | } + /// | - `g` is later dropped here + /// ``` + /// + /// Returns `true` if an async-await specific note was added to the diagnostic. + fn note_obligation_cause_for_async_await( + &self, + err: &mut DiagnosticBuilder<'_>, + obligation: &PredicateObligation<'tcx>, + ) -> bool { + debug!("note_obligation_cause_for_async_await: obligation.predicate={:?} \ + obligation.cause.span={:?}", obligation.predicate, obligation.cause.span); + let source_map = self.tcx.sess.source_map(); + + // Look into the obligation predicate to determine the type in the generator which meant + // that the predicate was not satisifed. + let (trait_ref, target_ty) = match obligation.predicate { + ty::Predicate::Trait(trait_predicate) => + (trait_predicate.skip_binder().trait_ref, trait_predicate.skip_binder().self_ty()), + _ => return false, + }; + debug!("note_obligation_cause_for_async_await: target_ty={:?}", target_ty); + + // Attempt to detect an async-await error by looking at the obligation causes, looking + // for only generators, generator witnesses, opaque types or `std::future::GenFuture` to + // be present. + // + // When a future does not implement a trait because of a captured type in one of the + // generators somewhere in the call stack, then the result is a chain of obligations. + // Given a `async fn` A that calls a `async fn` B which captures a non-send type and that + // future is passed as an argument to a function C which requires a `Send` type, then the + // chain looks something like this: + // + // - `BuiltinDerivedObligation` with a generator witness (B) + // - `BuiltinDerivedObligation` with a generator (B) + // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (B) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (B) + // - `BuiltinDerivedObligation` with a generator witness (A) + // - `BuiltinDerivedObligation` with a generator (A) + // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (A) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (A) + // - `BindingObligation` with `impl_send (Send requirement) + // + // The first obligations in the chain can be used to get the details of the type that is + // captured but the entire chain must be inspected to detect this case. + let mut generator = None; + let mut next_code = Some(&obligation.cause.code); + while let Some(code) = next_code { + debug!("note_obligation_cause_for_async_await: code={:?}", code); + match code { + ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) | + ObligationCauseCode::ImplDerivedObligation(derived_obligation) => { + debug!("note_obligation_cause_for_async_await: self_ty.kind={:?}", + derived_obligation.parent_trait_ref.self_ty().kind); + match derived_obligation.parent_trait_ref.self_ty().kind { + ty::Adt(ty::AdtDef { did, .. }, ..) if + self.tcx.is_diagnostic_item(sym::gen_future, *did) => {}, + ty::Generator(did, ..) => generator = generator.or(Some(did)), + ty::GeneratorWitness(_) | ty::Opaque(..) => {}, + _ => return false, + } + + next_code = Some(derived_obligation.parent_code.as_ref()); + }, + ObligationCauseCode::ItemObligation(_) | ObligationCauseCode::BindingObligation(..) + if generator.is_some() => break, + _ => return false, + } + } + + let generator_did = generator.expect("can only reach this if there was a generator"); + + // Only continue to add a note if the generator is from an `async` function. + let parent_node = self.tcx.parent(generator_did) + .and_then(|parent_did| self.tcx.hir().get_if_local(parent_did)); + debug!("note_obligation_cause_for_async_await: parent_node={:?}", parent_node); + if let Some(hir::Node::Item(hir::Item { + kind: hir::ItemKind::Fn(_, header, _, _), + .. + })) = parent_node { + debug!("note_obligation_cause_for_async_await: header={:?}", header); + if header.asyncness != hir::IsAsync::Async { + return false; + } + } + + let span = self.tcx.def_span(generator_did); + let tables = self.tcx.typeck_tables_of(generator_did); + debug!("note_obligation_cause_for_async_await: generator_did={:?} span={:?} ", + generator_did, span); + + // Look for a type inside the generator interior that matches the target type to get + // a span. + let target_span = tables.generator_interior_types.iter() + .find(|ty::GeneratorInteriorTypeCause { ty, .. }| ty::TyS::same_type(*ty, target_ty)) + .map(|ty::GeneratorInteriorTypeCause { span, scope_span, .. }| + (span, source_map.span_to_snippet(*span), scope_span)); + if let Some((target_span, Ok(snippet), scope_span)) = target_span { + // Look at the last interior type to get a span for the `.await`. + let await_span = tables.generator_interior_types.iter().map(|i| i.span).last().unwrap(); + let mut span = MultiSpan::from_span(await_span); + span.push_span_label( + await_span, format!("await occurs here, with `{}` maybe used later", snippet)); + + span.push_span_label(*target_span, format!("has type `{}`", target_ty)); + + // If available, use the scope span to annotate the drop location. + if let Some(scope_span) = scope_span { + span.push_span_label( + source_map.end_point(*scope_span), + format!("`{}` is later dropped here", snippet), + ); + } + + err.span_note(span, &format!( + "future does not implement `{}` as this value is used across an await", + trait_ref, + )); + + // Add a note for the item obligation that remains - normally a note pointing to the + // bound that introduced the obligation (e.g. `T: Send`). + debug!("note_obligation_cause_for_async_await: next_code={:?}", next_code); + self.note_obligation_cause_code( + err, + &obligation.predicate, + next_code.unwrap(), + &mut Vec::new(), + ); + + true + } else { + false + } } fn note_obligation_cause_code(&self, diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs index 6c5d9a6dfdf22..7626ecd424347 100644 --- a/src/librustc/ty/context.rs +++ b/src/librustc/ty/context.rs @@ -288,6 +288,34 @@ pub struct ResolvedOpaqueTy<'tcx> { pub substs: SubstsRef<'tcx>, } +/// Whenever a value may be live across a generator yield, the type of that value winds up in the +/// `GeneratorInteriorTypeCause` struct. This struct adds additional information about such +/// captured types that can be useful for diagnostics. In particular, it stores the span that +/// caused a given type to be recorded, along with the scope that enclosed the value (which can +/// be used to find the await that the value is live across). +/// +/// For example: +/// +/// ```ignore (pseudo-Rust) +/// async move { +/// let x: T = ...; +/// foo.await +/// ... +/// } +/// ``` +/// +/// Here, we would store the type `T`, the span of the value `x`, and the "scope-span" for +/// the scope that contains `x`. +#[derive(RustcEncodable, RustcDecodable, Clone, Debug, Eq, Hash, HashStable, PartialEq)] +pub struct GeneratorInteriorTypeCause<'tcx> { + /// Type of the captured binding. + pub ty: Ty<'tcx>, + /// Span of the binding that was captured. + pub span: Span, + /// Span of the scope of the captured binding. + pub scope_span: Option, +} + #[derive(RustcEncodable, RustcDecodable, Debug)] pub struct TypeckTables<'tcx> { /// The HirId::owner all ItemLocalIds in this table are relative to. @@ -397,6 +425,10 @@ pub struct TypeckTables<'tcx> { /// leading to the member of the struct or tuple that is used instead of the /// entire variable. pub upvar_list: ty::UpvarListMap, + + /// Stores the type, span and optional scope span of all types + /// that are live across the yield of this generator (if a generator). + pub generator_interior_types: Vec>, } impl<'tcx> TypeckTables<'tcx> { @@ -422,6 +454,7 @@ impl<'tcx> TypeckTables<'tcx> { free_region_map: Default::default(), concrete_opaque_types: Default::default(), upvar_list: Default::default(), + generator_interior_types: Default::default(), } } @@ -729,6 +762,7 @@ impl<'a, 'tcx> HashStable> for TypeckTables<'tcx> { ref free_region_map, ref concrete_opaque_types, ref upvar_list, + ref generator_interior_types, } = *self; @@ -773,6 +807,7 @@ impl<'a, 'tcx> HashStable> for TypeckTables<'tcx> { free_region_map.hash_stable(hcx, hasher); concrete_opaque_types.hash_stable(hcx, hasher); upvar_list.hash_stable(hcx, hasher); + generator_interior_types.hash_stable(hcx, hasher); }) } } diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs index 731aca854a422..683c977499c6a 100644 --- a/src/librustc/ty/mod.rs +++ b/src/librustc/ty/mod.rs @@ -75,7 +75,7 @@ pub use self::binding::BindingMode; pub use self::binding::BindingMode::*; pub use self::context::{TyCtxt, FreeRegionInfo, AllArenas, tls, keep_local}; -pub use self::context::{Lift, TypeckTables, CtxtInterners, GlobalCtxt}; +pub use self::context::{Lift, GeneratorInteriorTypeCause, TypeckTables, CtxtInterners, GlobalCtxt}; pub use self::context::{ UserTypeAnnotationIndex, UserType, CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, ResolvedOpaqueTy, diff --git a/src/librustc_typeck/check/generator_interior.rs b/src/librustc_typeck/check/generator_interior.rs index d2d3854d2758c..4608eb51df74e 100644 --- a/src/librustc_typeck/check/generator_interior.rs +++ b/src/librustc_typeck/check/generator_interior.rs @@ -14,7 +14,7 @@ use crate::util::nodemap::FxHashMap; struct InteriorVisitor<'a, 'tcx> { fcx: &'a FnCtxt<'a, 'tcx>, - types: FxHashMap, usize>, + types: FxHashMap, usize>, region_scope_tree: &'tcx region::ScopeTree, expr_count: usize, kind: hir::GeneratorKind, @@ -83,7 +83,12 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> { } else { // Map the type to the number of types added before it let entries = self.types.len(); - self.types.entry(&ty).or_insert(entries); + let scope_span = scope.map(|s| s.span(self.fcx.tcx, self.region_scope_tree)); + self.types.entry(ty::GeneratorInteriorTypeCause { + span: source_span, + ty: &ty, + scope_span + }).or_insert(entries); } } else { debug!("no type in expr = {:?}, count = {:?}, span = {:?}", @@ -118,8 +123,12 @@ pub fn resolve_interior<'a, 'tcx>( // Sort types by insertion order types.sort_by_key(|t| t.1); + // Store the generator types and spans into the tables for this generator. + let interior_types = types.iter().cloned().map(|t| t.0).collect::>(); + visitor.fcx.inh.tables.borrow_mut().generator_interior_types = interior_types; + // Extract type components - let type_list = fcx.tcx.mk_type_list(types.into_iter().map(|t| t.0)); + let type_list = fcx.tcx.mk_type_list(types.into_iter().map(|t| (t.0).ty)); // The types in the generator interior contain lifetimes local to the generator itself, // which should not be exposed outside of the generator. Therefore, we replace these diff --git a/src/librustc_typeck/check/writeback.rs b/src/librustc_typeck/check/writeback.rs index de78c1cdfaba3..99d62d198a9fd 100644 --- a/src/librustc_typeck/check/writeback.rs +++ b/src/librustc_typeck/check/writeback.rs @@ -58,6 +58,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { wbcx.visit_free_region_map(); wbcx.visit_user_provided_tys(); wbcx.visit_user_provided_sigs(); + wbcx.visit_generator_interior_types(); let used_trait_imports = mem::replace( &mut self.tables.borrow_mut().used_trait_imports, @@ -430,6 +431,12 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> { } } + fn visit_generator_interior_types(&mut self) { + let fcx_tables = self.fcx.tables.borrow(); + debug_assert_eq!(fcx_tables.local_id_root, self.tables.local_id_root); + self.tables.generator_interior_types = fcx_tables.generator_interior_types.clone(); + } + fn visit_opaque_types(&mut self, span: Span) { for (&def_id, opaque_defn) in self.fcx.opaque_types.borrow().iter() { let hir_id = self.tcx().hir().as_local_hir_id(def_id).unwrap(); diff --git a/src/libstd/future.rs b/src/libstd/future.rs index 0406549ff0791..c65f71fb1a4e2 100644 --- a/src/libstd/future.rs +++ b/src/libstd/future.rs @@ -26,6 +26,7 @@ pub fn from_generator>(x: T) -> impl Future>(T); // We rely on the fact that async/await futures are immovable in order to create diff --git a/src/test/ui/async-await/async-fn-nonsend.stderr b/src/test/ui/async-await/async-fn-nonsend.stderr index 001e0b1cad305..696bd5c39d283 100644 --- a/src/test/ui/async-await/async-fn-nonsend.stderr +++ b/src/test/ui/async-await/async-fn-nonsend.stderr @@ -9,9 +9,9 @@ LL | assert_send(local_dropped_before_await()); | = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<()>` = note: required because it appears within the type `impl std::fmt::Debug` - = note: required because it appears within the type `{impl std::fmt::Debug, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}` - = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:21:39: 26:2 {impl std::fmt::Debug, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]` - = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:21:39: 26:2 {impl std::fmt::Debug, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]>` + = note: required because it appears within the type `{impl std::fmt::Debug, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}` + = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:21:39: 26:2 {impl std::fmt::Debug, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]` + = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:21:39: 26:2 {impl std::fmt::Debug, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]>` = note: required because it appears within the type `impl std::future::Future` = note: required because it appears within the type `impl std::future::Future` @@ -26,9 +26,9 @@ LL | assert_send(non_send_temporary_in_match()); | = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<()>` = note: required because it appears within the type `impl std::fmt::Debug` - = note: required because it appears within the type `{fn(impl std::fmt::Debug) -> std::option::Option {std::option::Option::::Some}, fn() -> impl std::fmt::Debug {non_send}, impl std::fmt::Debug, std::option::Option, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}` - = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:28:40: 37:2 {fn(impl std::fmt::Debug) -> std::option::Option {std::option::Option::::Some}, fn() -> impl std::fmt::Debug {non_send}, impl std::fmt::Debug, std::option::Option, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]` - = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:28:40: 37:2 {fn(impl std::fmt::Debug) -> std::option::Option {std::option::Option::::Some}, fn() -> impl std::fmt::Debug {non_send}, impl std::fmt::Debug, std::option::Option, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]>` + = note: required because it appears within the type `{fn(impl std::fmt::Debug) -> std::option::Option {std::option::Option::::Some}, fn() -> impl std::fmt::Debug {non_send}, impl std::fmt::Debug, std::option::Option, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}` + = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:28:40: 37:2 {fn(impl std::fmt::Debug) -> std::option::Option {std::option::Option::::Some}, fn() -> impl std::fmt::Debug {non_send}, impl std::fmt::Debug, std::option::Option, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]` + = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:28:40: 37:2 {fn(impl std::fmt::Debug) -> std::option::Option {std::option::Option::::Some}, fn() -> impl std::fmt::Debug {non_send}, impl std::fmt::Debug, std::option::Option, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]>` = note: required because it appears within the type `impl std::future::Future` = note: required because it appears within the type `impl std::future::Future` @@ -45,9 +45,9 @@ LL | assert_send(non_sync_with_method_call()); = note: required because of the requirements on the impl of `std::marker::Send` for `&mut dyn std::fmt::Write` = note: required because it appears within the type `std::fmt::Formatter<'_>` = note: required because of the requirements on the impl of `std::marker::Send` for `&mut std::fmt::Formatter<'_>` - = note: required because it appears within the type `for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}` - = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]` - = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]>` + = note: required because it appears within the type `for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}` + = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]` + = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]>` = note: required because it appears within the type `impl std::future::Future` = note: required because it appears within the type `impl std::future::Future` @@ -68,9 +68,9 @@ LL | assert_send(non_sync_with_method_call()); = note: required because of the requirements on the impl of `std::marker::Send` for `std::slice::Iter<'_, std::fmt::ArgumentV1<'_>>` = note: required because it appears within the type `std::fmt::Formatter<'_>` = note: required because of the requirements on the impl of `std::marker::Send` for `&mut std::fmt::Formatter<'_>` - = note: required because it appears within the type `for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}` - = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]` - = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, ()}]>` + = note: required because it appears within the type `for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}` + = note: required because it appears within the type `[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]` + = note: required because it appears within the type `std::future::GenFuture<[static generator@$DIR/async-fn-nonsend.rs:39:38: 45:2 for<'r, 's> {&'r mut std::fmt::Formatter<'s>, bool, bool, fn() -> impl std::future::Future {fut}, impl std::future::Future, impl std::future::Future, ()}]>` = note: required because it appears within the type `impl std::future::Future` = note: required because it appears within the type `impl std::future::Future` diff --git a/src/test/ui/async-await/issue-64130-non-send-future-diags.rs b/src/test/ui/async-await/issue-64130-non-send-future-diags.rs new file mode 100644 index 0000000000000..1936d1a2ed56e --- /dev/null +++ b/src/test/ui/async-await/issue-64130-non-send-future-diags.rs @@ -0,0 +1,25 @@ +// edition:2018 + +use std::sync::Mutex; + +fn is_send(t: T) { + +} + +async fn foo() { + bar(&Mutex::new(22)).await; +} + +async fn bar(x: &Mutex) { + let g = x.lock().unwrap(); + baz().await; +} + +async fn baz() { + +} + +fn main() { + is_send(foo()); + //~^ ERROR `std::sync::MutexGuard<'_, u32>` cannot be sent between threads safely [E0277] +} diff --git a/src/test/ui/async-await/issue-64130-non-send-future-diags.stderr b/src/test/ui/async-await/issue-64130-non-send-future-diags.stderr new file mode 100644 index 0000000000000..9e9fc52e30b7f --- /dev/null +++ b/src/test/ui/async-await/issue-64130-non-send-future-diags.stderr @@ -0,0 +1,23 @@ +error[E0277]: `std::sync::MutexGuard<'_, u32>` cannot be sent between threads safely + --> $DIR/issue-64130-non-send-future-diags.rs:23:5 + | +LL | fn is_send(t: T) { + | ------- ---- required by this bound in `is_send` +... +LL | is_send(foo()); + | ^^^^^^^ `std::sync::MutexGuard<'_, u32>` cannot be sent between threads safely + | + = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::sync::MutexGuard<'_, u32>` +note: future does not implement `std::marker::Send` as this value is used across an await + --> $DIR/issue-64130-non-send-future-diags.rs:15:5 + | +LL | let g = x.lock().unwrap(); + | - has type `std::sync::MutexGuard<'_, u32>` +LL | baz().await; + | ^^^^^^^^^^^ await occurs here, with `g` maybe used later +LL | } + | - `g` is later dropped here + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0277`.