Warn for #[must_use] in tuples
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7840a0b753
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@ -47,42 +47,14 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
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return;
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}
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let t = cx.tables.expr_ty(&expr);
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let type_permits_lack_of_use = if t.is_unit()
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let ty = cx.tables.expr_ty(&expr);
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let type_permits_lack_of_use = if ty.is_unit()
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|| cx.tcx.is_ty_uninhabited_from(
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cx.tcx.hir().get_module_parent_by_hir_id(expr.hir_id), t)
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cx.tcx.hir().get_module_parent_by_hir_id(expr.hir_id), ty)
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{
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true
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} else {
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match t.sty {
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ty::Adt(def, _) => check_must_use(cx, def.did, s.span, "", ""),
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ty::Opaque(def, _) => {
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let mut must_use = false;
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for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
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if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
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let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
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if check_must_use(cx, trait_ref.def_id, s.span, "implementer of ", "") {
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must_use = true;
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break;
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}
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}
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}
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must_use
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}
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ty::Dynamic(binder, _) => {
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let mut must_use = false;
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for predicate in binder.skip_binder().iter() {
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if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
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if check_must_use(cx, trait_ref.def_id, s.span, "", " trait object") {
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must_use = true;
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break;
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}
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}
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}
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must_use
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}
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_ => false,
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}
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check_must_use_ty(cx, ty, s.span)
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};
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let mut fn_warned = false;
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@ -108,7 +80,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
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_ => None
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};
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if let Some(def_id) = maybe_def_id {
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fn_warned = check_must_use(cx, def_id, s.span, "return value of ", "");
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fn_warned = check_must_use_def(cx, def_id, s.span, "return value of ", "");
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} else if type_permits_lack_of_use {
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// We don't warn about unused unit or uninhabited types.
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// (See https://github.com/rust-lang/rust/issues/43806 for details.)
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@ -162,10 +134,55 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
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cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
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}
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fn check_must_use(
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// Returns whether an error has been emitted (and thus another does not need to be later).
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fn check_must_use_ty(
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cx: &LateContext<'_, '_>,
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ty: ty::Ty<'_>,
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span: Span,
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) -> bool {
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match ty.sty {
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ty::Adt(def, _) => check_must_use_def(cx, def.did, span, "", ""),
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ty::Opaque(def, _) => {
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let mut has_emitted = false;
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for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
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if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
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let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
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let def_id = trait_ref.def_id;
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if check_must_use_def(cx, def_id, span, "implementer of ", "") {
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has_emitted = true;
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break;
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}
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}
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}
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has_emitted
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}
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ty::Dynamic(binder, _) => {
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let mut has_emitted = false;
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for predicate in binder.skip_binder().iter() {
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if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
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let def_id = trait_ref.def_id;
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if check_must_use_def(cx, def_id, span, "", " trait object") {
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has_emitted = true;
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break;
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}
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}
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}
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has_emitted
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}
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ty::Tuple(ref tys) => {
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tys.iter().map(|k| k.expect_ty()).any(|ty| {
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check_must_use_ty(cx, ty, span)
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})
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}
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_ => false,
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}
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}
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// Returns whether an error has been emitted (and thus another does not need to be later).
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fn check_must_use_def(
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cx: &LateContext<'_, '_>,
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def_id: DefId,
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sp: Span,
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span: Span,
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descr_pre_path: &str,
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descr_post_path: &str,
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) -> bool {
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@ -173,7 +190,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
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if attr.check_name(sym::must_use) {
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let msg = format!("unused {}`{}`{} that must be used",
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descr_pre_path, cx.tcx.def_path_str(def_id), descr_post_path);
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let mut err = cx.struct_span_lint(UNUSED_MUST_USE, sp, &msg);
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let mut err = cx.struct_span_lint(UNUSED_MUST_USE, span, &msg);
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// check for #[must_use = "..."]
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if let Some(note) = attr.value_str() {
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err.note(¬e.as_str());
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