diff --git a/clippy_lints/src/functions/must_use.rs b/clippy_lints/src/functions/must_use.rs index 1e9e826631c..d0ad2628264 100644 --- a/clippy_lints/src/functions/must_use.rs +++ b/clippy_lints/src/functions/must_use.rs @@ -1,7 +1,9 @@ +use hir::FnSig; use rustc_ast::ast::Attribute; use rustc_errors::Applicability; use rustc_hir::def_id::DefIdSet; use rustc_hir::{self as hir, def::Res, QPath}; +use rustc_infer::infer::TyCtxtInferExt; use rustc_lint::{LateContext, LintContext}; use rustc_middle::{ lint::in_external_macro, @@ -27,7 +29,7 @@ pub(super) fn check_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_> let is_public = cx.effective_visibilities.is_exported(item.owner_id.def_id); let fn_header_span = item.span.with_hi(sig.decl.output.span().hi()); if let Some(attr) = attr { - check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr); + check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr, sig); } else if is_public && !is_proc_macro(attrs) && !attrs.iter().any(|a| a.has_name(sym::no_mangle)) { check_must_use_candidate( cx, @@ -49,7 +51,7 @@ pub(super) fn check_impl_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::Imp let attrs = cx.tcx.hir().attrs(item.hir_id()); let attr = cx.tcx.get_attr(item.owner_id, sym::must_use); if let Some(attr) = attr { - check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr); + check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr, sig); } else if is_public && !is_proc_macro(attrs) && trait_ref_of_method(cx, item.owner_id.def_id).is_none() { check_must_use_candidate( cx, @@ -72,7 +74,7 @@ pub(super) fn check_trait_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::Tr let attrs = cx.tcx.hir().attrs(item.hir_id()); let attr = cx.tcx.get_attr(item.owner_id, sym::must_use); if let Some(attr) = attr { - check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr); + check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr, sig); } else if let hir::TraitFn::Provided(eid) = *eid { let body = cx.tcx.hir().body(eid); if attr.is_none() && is_public && !is_proc_macro(attrs) { @@ -97,6 +99,7 @@ fn check_needless_must_use( item_span: Span, fn_header_span: Span, attr: &Attribute, + sig: &FnSig<'_>, ) { if in_external_macro(cx.sess(), item_span) { return; @@ -112,6 +115,15 @@ fn check_needless_must_use( }, ); } else if attr.value_str().is_none() && is_must_use_ty(cx, return_ty(cx, item_id)) { + // Ignore async functions unless Future::Output type is a must_use type + if sig.header.is_async() { + let infcx = cx.tcx.infer_ctxt().build(); + if let Some(future_ty) = infcx.get_impl_future_output_ty(return_ty(cx, item_id)) + && !is_must_use_ty(cx, future_ty) { + return; + } + } + span_lint_and_help( cx, DOUBLE_MUST_USE, diff --git a/tests/ui/double_must_use.rs b/tests/ui/double_must_use.rs index 05e087b08bc..26a387b3cf0 100644 --- a/tests/ui/double_must_use.rs +++ b/tests/ui/double_must_use.rs @@ -21,6 +21,17 @@ pub fn must_use_with_note() -> Result<(), ()> { unimplemented!(); } +// vvvv Should not lint (#10486) +#[must_use] +async fn async_must_use() -> usize { + unimplemented!(); +} + +#[must_use] +async fn async_must_use_result() -> Result<(), ()> { + Ok(()) +} + fn main() { must_use_result(); must_use_tuple(); diff --git a/tests/ui/double_must_use.stderr b/tests/ui/double_must_use.stderr index 3d34557a881..49ab2ea3e12 100644 --- a/tests/ui/double_must_use.stderr +++ b/tests/ui/double_must_use.stderr @@ -23,5 +23,13 @@ LL | pub fn must_use_array() -> [Result<(), ()>; 1] { | = help: either add some descriptive text or remove the attribute -error: aborting due to 3 previous errors +error: this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]` + --> $DIR/double_must_use.rs:31:1 + | +LL | async fn async_must_use_result() -> Result<(), ()> { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = help: either add some descriptive text or remove the attribute + +error: aborting due to 4 previous errors