1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::return_ty;
3 use rustc_hir::intravisit::FnKind;
4 use rustc_hir::{Body, FnDecl, HirId};
5 use rustc_infer::infer::TyCtxtInferExt;
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_middle::ty::{self, AliasTy, Clause, EarlyBinder, PredicateKind};
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 use rustc_span::{sym, Span};
10 use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt;
11 use rustc_trait_selection::traits::{self, FulfillmentError};
13 declare_clippy_lint! {
15 /// This lint requires Future implementations returned from
16 /// functions and methods to implement the `Send` marker trait. It is mostly
17 /// used by library authors (public and internal) that target an audience where
18 /// multithreaded executors are likely to be used for running these Futures.
20 /// ### Why is this bad?
21 /// A Future implementation captures some state that it
22 /// needs to eventually produce its final value. When targeting a multithreaded
23 /// executor (which is the norm on non-embedded devices) this means that this
24 /// state may need to be transported to other threads, in other words the
25 /// whole Future needs to implement the `Send` marker trait. If it does not,
26 /// then the resulting Future cannot be submitted to a thread pool in the
27 /// end user’s code.
29 /// Especially for generic functions it can be confusing to leave the
30 /// discovery of this problem to the end user: the reported error location
31 /// will be far from its cause and can in many cases not even be fixed without
32 /// modifying the library where the offending Future implementation is
37 /// async fn not_send(bytes: std::rc::Rc<[u8]>) {}
41 /// async fn is_send(bytes: std::sync::Arc<[u8]>) {}
43 #[clippy::version = "1.44.0"]
46 "public Futures must be Send"
49 declare_lint_pass!(FutureNotSend => [FUTURE_NOT_SEND]);
51 impl<'tcx> LateLintPass<'tcx> for FutureNotSend {
54 cx: &LateContext<'tcx>,
56 decl: &'tcx FnDecl<'tcx>,
61 if let FnKind::Closure = kind {
64 let ret_ty = return_ty(cx, hir_id);
65 if let ty::Alias(ty::Opaque, AliasTy { def_id, substs }) = *ret_ty.kind() {
66 let preds = cx.tcx.explicit_item_bounds(def_id);
67 let mut is_future = false;
68 for &(p, _span) in preds {
69 let p = EarlyBinder(p).subst(cx.tcx, substs);
70 if let Some(trait_pred) = p.to_opt_poly_trait_pred() {
71 if Some(trait_pred.skip_binder().trait_ref.def_id) == cx.tcx.lang_items().future_trait() {
78 let send_trait = cx.tcx.get_diagnostic_item(sym::Send).unwrap();
79 let span = decl.output.span();
80 let infcx = cx.tcx.infer_ctxt().build();
81 let cause = traits::ObligationCause::misc(span, hir_id);
82 let send_errors = traits::fully_solve_bound(&infcx, cause, cx.param_env, ret_ty, send_trait);
83 if !send_errors.is_empty() {
88 "future cannot be sent between threads safely",
90 for FulfillmentError { obligation, .. } in send_errors {
93 .maybe_note_obligation_cause_for_async_await(db, &obligation);
94 if let PredicateKind::Clause(Clause::Trait(trait_pred)) =
95 obligation.predicate.kind().skip_binder()
98 "`{}` doesn't implement `{}`",
100 trait_pred.trait_ref.print_only_trait_path(),