diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs index 7eab7d21002..6383ca69fe5 100644 --- a/src/librustc_lint/unused.rs +++ b/src/librustc_lint/unused.rs @@ -60,19 +60,15 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults { } let t = cx.tables.expr_ty(&expr); - // FIXME(varkor): replace with `t.is_unit() || t.conservative_is_uninhabited()`. - let type_permits_no_use = match t.sty { - ty::Tuple(ref tys) if tys.is_empty() => true, - ty::Never => true, - ty::Adt(def, _) => { - if def.variants.is_empty() { - true - } else { - check_must_use(cx, def.did, s.span, "") - } + let type_permits_lack_of_use = if t.is_unit() + || cx.tcx.is_ty_uninhabited_from(cx.tcx.hir.get_module_parent(expr.id), t) { + true + } else { + match t.sty { + ty::Adt(def, _) => check_must_use(cx, def.did, s.span, ""), + _ => false, } - _ => false, - }; + } let mut fn_warned = false; let mut op_warned = false; @@ -99,7 +95,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults { if let Some(def) = maybe_def { let def_id = def.def_id(); fn_warned = check_must_use(cx, def_id, s.span, "return value of "); - } else if type_permits_no_use { + } else if type_permits_lack_of_use { // We don't warn about unused unit or uninhabited types. // (See https://github.com/rust-lang/rust/issues/43806 for details.) return; @@ -148,7 +144,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults { op_warned = true; } - if !(type_permits_no_use || fn_warned || op_warned) { + if !(type_permits_lack_of_use || fn_warned || op_warned) { cx.span_lint(UNUSED_RESULTS, s.span, "unused result"); }