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use clippy_utils::diagnostics::span_lint_hir_and_then;
use clippy_utils::source::snippet;
use clippy_utils::ty::implements_trait;
use rustc_errors::Applicability;
use rustc_hir::{AsyncGeneratorKind, Body, BodyId, ExprKind, GeneratorKind, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for async blocks that yield values of types
/// that can themselves be awaited.
///
/// ### Why is this bad?
/// An await is likely missing.
///
/// ### Example
/// ```rust
/// async fn foo() {}
///
/// fn bar() {
/// let x = async {
/// foo()
/// };
/// }
/// ```
///
/// Use instead:
/// ```rust
/// async fn foo() {}
///
/// fn bar() {
/// let x = async {
/// foo().await
/// };
/// }
/// ```
#[clippy::version = "1.48.0"]
pub ASYNC_YIELDS_ASYNC,
correctness,
"async blocks that return a type that can be awaited"
}
declare_lint_pass!(AsyncYieldsAsync => [ASYNC_YIELDS_ASYNC]);
impl<'tcx> LateLintPass<'tcx> for AsyncYieldsAsync {
fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
use AsyncGeneratorKind::{Block, Closure};
// For functions, with explicitly defined types, don't warn.
// XXXkhuey maybe we should?
if let Some(GeneratorKind::Async(Block | Closure)) = body.generator_kind {
if let Some(future_trait_def_id) = cx.tcx.lang_items().future_trait() {
let body_id = BodyId {
hir_id: body.value.hir_id,
};
let typeck_results = cx.tcx.typeck_body(body_id);
let expr_ty = typeck_results.expr_ty(body.value);
if implements_trait(cx, expr_ty, future_trait_def_id, &[]) {
let return_expr_span = match &body.value.kind {
// XXXkhuey there has to be a better way.
ExprKind::Block(block, _) => block.expr.map(|e| e.span),
ExprKind::Path(QPath::Resolved(_, path)) => Some(path.span),
_ => None,
};
if let Some(return_expr_span) = return_expr_span {
span_lint_hir_and_then(
cx,
ASYNC_YIELDS_ASYNC,
body.value.hir_id,
return_expr_span,
"an async construct yields a type which is itself awaitable",
|db| {
db.span_label(body.value.span, "outer async construct");
db.span_label(return_expr_span, "awaitable value not awaited");
db.span_suggestion(
return_expr_span,
"consider awaiting this value",
format!("{}.await", snippet(cx, return_expr_span, "..")),
Applicability::MaybeIncorrect,
);
},
);
}
}
}
}
}
}
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