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use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::return_ty;
use rustc_hir::intravisit::FnKind;
use rustc_hir::{Body, FnDecl};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, AliasTy, Clause, EarlyBinder, PredicateKind};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::def_id::LocalDefId;
use rustc_span::{sym, Span};
use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt;
use rustc_trait_selection::traits::{self, FulfillmentError};
declare_clippy_lint! {
/// ### What it does
/// This lint requires Future implementations returned from
/// functions and methods to implement the `Send` marker trait. It is mostly
/// used by library authors (public and internal) that target an audience where
/// multithreaded executors are likely to be used for running these Futures.
///
/// ### Why is this bad?
/// A Future implementation captures some state that it
/// needs to eventually produce its final value. When targeting a multithreaded
/// executor (which is the norm on non-embedded devices) this means that this
/// state may need to be transported to other threads, in other words the
/// whole Future needs to implement the `Send` marker trait. If it does not,
/// then the resulting Future cannot be submitted to a thread pool in the
/// end user’s code.
///
/// Especially for generic functions it can be confusing to leave the
/// discovery of this problem to the end user: the reported error location
/// will be far from its cause and can in many cases not even be fixed without
/// modifying the library where the offending Future implementation is
/// produced.
///
/// ### Example
/// ```rust
/// async fn not_send(bytes: std::rc::Rc<[u8]>) {}
/// ```
/// Use instead:
/// ```rust
/// async fn is_send(bytes: std::sync::Arc<[u8]>) {}
/// ```
#[clippy::version = "1.44.0"]
pub FUTURE_NOT_SEND,
nursery,
"public Futures must be Send"
}
declare_lint_pass!(FutureNotSend => [FUTURE_NOT_SEND]);
impl<'tcx> LateLintPass<'tcx> for FutureNotSend {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
kind: FnKind<'tcx>,
decl: &'tcx FnDecl<'tcx>,
_: &'tcx Body<'tcx>,
_: Span,
fn_def_id: LocalDefId,
) {
if let FnKind::Closure = kind {
return;
}
let ret_ty = return_ty(cx, cx.tcx.hir().local_def_id_to_hir_id(fn_def_id).expect_owner());
if let ty::Alias(ty::Opaque, AliasTy { def_id, substs, .. }) = *ret_ty.kind() {
let preds = cx.tcx.explicit_item_bounds(def_id);
let mut is_future = false;
for &(p, _span) in preds {
let p = EarlyBinder(p).subst(cx.tcx, substs);
if let Some(trait_pred) = p.to_opt_poly_trait_pred() {
if Some(trait_pred.skip_binder().trait_ref.def_id) == cx.tcx.lang_items().future_trait() {
is_future = true;
break;
}
}
}
if is_future {
let send_trait = cx.tcx.get_diagnostic_item(sym::Send).unwrap();
let span = decl.output.span();
let infcx = cx.tcx.infer_ctxt().build();
let cause = traits::ObligationCause::misc(span, fn_def_id);
let send_errors = traits::fully_solve_bound(&infcx, cause, cx.param_env, ret_ty, send_trait);
if !send_errors.is_empty() {
span_lint_and_then(
cx,
FUTURE_NOT_SEND,
span,
"future cannot be sent between threads safely",
|db| {
for FulfillmentError { obligation, .. } in send_errors {
infcx
.err_ctxt()
.maybe_note_obligation_cause_for_async_await(db, &obligation);
if let PredicateKind::Clause(Clause::Trait(trait_pred)) =
obligation.predicate.kind().skip_binder()
{
db.note(&format!(
"`{}` doesn't implement `{}`",
trait_pred.self_ty(),
trait_pred.trait_ref.print_only_trait_path(),
));
}
}
},
);
}
}
}
}
}
|
