1 use crate::utils::{implements_trait, snippet, span_lint_and_then};
2 use rustc_errors::Applicability;
3 use rustc_hir::{AsyncGeneratorKind, Body, BodyId, ExprKind, GeneratorKind, QPath};
4 use rustc_lint::{LateContext, LateLintPass};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 /// Checks for async blocks that yield values of types that can themselves
12 /// **Why is this bad?**
13 /// An await is likely missing.
15 /// **Known problems:** None.
38 pub ASYNC_YIELDS_ASYNC,
40 "async blocks that return a type that can be awaited"
43 declare_lint_pass!(AsyncYieldsAsync => [ASYNC_YIELDS_ASYNC]);
45 impl<'tcx> LateLintPass<'tcx> for AsyncYieldsAsync {
46 fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
47 use AsyncGeneratorKind::{Block, Closure};
48 // For functions, with explicitly defined types, don't warn.
49 // XXXkhuey maybe we should?
50 if let Some(GeneratorKind::Async(Block | Closure)) = body.generator_kind {
51 if let Some(future_trait_def_id) = cx.tcx.lang_items().future_trait() {
52 let body_id = BodyId {
53 hir_id: body.value.hir_id,
55 let def_id = cx.tcx.hir().body_owner_def_id(body_id);
56 let typeck_results = cx.tcx.typeck(def_id);
57 let expr_ty = typeck_results.expr_ty(&body.value);
59 if implements_trait(cx, expr_ty, future_trait_def_id, &[]) {
60 let return_expr_span = match &body.value.kind {
61 // XXXkhuey there has to be a better way.
62 ExprKind::Block(block, _) => block.expr.map(|e| e.span),
63 ExprKind::Path(QPath::Resolved(_, path)) => Some(path.span),
66 if let Some(return_expr_span) = return_expr_span {
71 "an async construct yields a type which is itself awaitable",
73 db.span_label(body.value.span, "outer async construct");
74 db.span_label(return_expr_span, "awaitable value not awaited");
77 "consider awaiting this value",
78 format!("{}.await", snippet(cx, return_expr_span, "..")),
79 Applicability::MaybeIncorrect,