diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index 036820c6d7fa1..d540b3f7e40a3 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -1,7 +1,7 @@
use rustc::hir::def::{Res, DefKind};
use rustc::hir::def_id::DefId;
use rustc::lint;
-use rustc::ty;
+use rustc::ty::{self, Ty};
use rustc::ty::adjustment;
use rustc_data_structures::fx::FxHashMap;
use lint::{LateContext, EarlyContext, LintContext, LintArray};
@@ -47,43 +47,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
return;
}
- let t = cx.tables.expr_ty(&expr);
- let type_permits_lack_of_use = if t.is_unit()
- || cx.tcx.is_ty_uninhabited_from(
- cx.tcx.hir().get_module_parent_by_hir_id(expr.hir_id), t)
- {
- true
- } else {
- match t.sty {
- ty::Adt(def, _) => check_must_use(cx, def.did, s.span, "", ""),
- ty::Opaque(def, _) => {
- let mut must_use = false;
- for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
- if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
- let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
- if check_must_use(cx, trait_ref.def_id, s.span, "implementer of ", "") {
- must_use = true;
- break;
- }
- }
- }
- must_use
- }
- ty::Dynamic(binder, _) => {
- let mut must_use = false;
- for predicate in binder.skip_binder().iter() {
- if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
- if check_must_use(cx, trait_ref.def_id, s.span, "", " trait object") {
- must_use = true;
- break;
- }
- }
- }
- must_use
- }
- _ => false,
- }
- };
+ let ty = cx.tables.expr_ty(&expr);
+ let type_permits_lack_of_use = check_must_use_ty(cx, ty, &expr, s.span, "");
let mut fn_warned = false;
let mut op_warned = false;
@@ -108,7 +73,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
_ => None
};
if let Some(def_id) = maybe_def_id {
- fn_warned = check_must_use(cx, def_id, s.span, "return value of ", "");
+ fn_warned = check_must_use_def(cx, def_id, s.span, "return value of ", "");
} 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.)
@@ -162,10 +127,75 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
}
- fn check_must_use(
+ // Returns whether an error has been emitted (and thus another does not need to be later).
+ fn check_must_use_ty<'tcx>(
+ cx: &LateContext<'_, 'tcx>,
+ ty: Ty<'tcx>,
+ expr: &hir::Expr,
+ span: Span,
+ descr_post_path: &str,
+ ) -> bool {
+ if ty.is_unit() || cx.tcx.is_ty_uninhabited_from(
+ cx.tcx.hir().get_module_parent_by_hir_id(expr.hir_id), ty)
+ {
+ return true;
+ }
+
+ match ty.sty {
+ ty::Adt(def, _) => check_must_use_def(cx, def.did, span, "", descr_post_path),
+ ty::Opaque(def, _) => {
+ let mut has_emitted = false;
+ for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
+ if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
+ let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
+ let def_id = trait_ref.def_id;
+ if check_must_use_def(cx, def_id, span, "implementer of ", "") {
+ has_emitted = true;
+ break;
+ }
+ }
+ }
+ has_emitted
+ }
+ ty::Dynamic(binder, _) => {
+ let mut has_emitted = false;
+ for predicate in binder.skip_binder().iter() {
+ if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
+ let def_id = trait_ref.def_id;
+ if check_must_use_def(cx, def_id, span, "", " trait object") {
+ has_emitted = true;
+ break;
+ }
+ }
+ }
+ has_emitted
+ }
+ ty::Tuple(ref tys) => {
+ let mut has_emitted = false;
+ let spans = if let hir::ExprKind::Tup(comps) = &expr.node {
+ debug_assert_eq!(comps.len(), tys.len());
+ comps.iter().map(|e| e.span).collect()
+ } else {
+ vec![]
+ };
+ for (i, ty) in tys.iter().map(|k| k.expect_ty()).enumerate() {
+ let descr_post_path = &format!(" in tuple element {}", i);
+ let span = *spans.get(i).unwrap_or(&span);
+ if check_must_use_ty(cx, ty, expr, span, descr_post_path) {
+ has_emitted = true;
+ }
+ }
+ has_emitted
+ }
+ _ => false,
+ }
+ }
+
+ // Returns whether an error has been emitted (and thus another does not need to be later).
+ fn check_must_use_def(
cx: &LateContext<'_, '_>,
def_id: DefId,
- sp: Span,
+ span: Span,
descr_pre_path: &str,
descr_post_path: &str,
) -> bool {
@@ -173,7 +203,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
if attr.check_name(sym::must_use) {
let msg = format!("unused {}`{}`{} that must be used",
descr_pre_path, cx.tcx.def_path_str(def_id), descr_post_path);
- let mut err = cx.struct_span_lint(UNUSED_MUST_USE, sp, &msg);
+ let mut err = cx.struct_span_lint(UNUSED_MUST_USE, span, &msg);
// check for #[must_use = "..."]
if let Some(note) = attr.value_str() {
err.note(¬e.as_str());
diff --git a/src/test/ui/lint/must_use-tuple.rs b/src/test/ui/lint/must_use-tuple.rs
new file mode 100644
index 0000000000000..f6b579a7f35cf
--- /dev/null
+++ b/src/test/ui/lint/must_use-tuple.rs
@@ -0,0 +1,17 @@
+#![deny(unused_must_use)]
+
+fn foo() -> (Result<(), ()>, ()) {
+ (Ok::<(), ()>(()), ())
+}
+
+fn main() {
+ (Ok::<(), ()>(()),); //~ ERROR unused `std::result::Result`
+
+ (Ok::<(), ()>(()), 0, Ok::<(), ()>(()), 5);
+ //~^ ERROR unused `std::result::Result`
+ //~^^ ERROR unused `std::result::Result`
+
+ foo(); //~ ERROR unused `std::result::Result`
+
+ ((Err::<(), ()>(()), ()), ()); //~ ERROR unused `std::result::Result`
+}
diff --git a/src/test/ui/lint/must_use-tuple.stderr b/src/test/ui/lint/must_use-tuple.stderr
new file mode 100644
index 0000000000000..45d2a439e52b0
--- /dev/null
+++ b/src/test/ui/lint/must_use-tuple.stderr
@@ -0,0 +1,47 @@
+error: unused `std::result::Result` in tuple element 0 that must be used
+ --> $DIR/must_use-tuple.rs:8:6
+ |
+LL | (Ok::<(), ()>(()),);
+ | ^^^^^^^^^^^^^^^^
+ |
+note: lint level defined here
+ --> $DIR/must_use-tuple.rs:1:9
+ |
+LL | #![deny(unused_must_use)]
+ | ^^^^^^^^^^^^^^^
+ = note: this `Result` may be an `Err` variant, which should be handled
+
+error: unused `std::result::Result` in tuple element 0 that must be used
+ --> $DIR/must_use-tuple.rs:10:6
+ |
+LL | (Ok::<(), ()>(()), 0, Ok::<(), ()>(()), 5);
+ | ^^^^^^^^^^^^^^^^
+ |
+ = note: this `Result` may be an `Err` variant, which should be handled
+
+error: unused `std::result::Result` in tuple element 2 that must be used
+ --> $DIR/must_use-tuple.rs:10:27
+ |
+LL | (Ok::<(), ()>(()), 0, Ok::<(), ()>(()), 5);
+ | ^^^^^^^^^^^^^^^^
+ |
+ = note: this `Result` may be an `Err` variant, which should be handled
+
+error: unused `std::result::Result` in tuple element 0 that must be used
+ --> $DIR/must_use-tuple.rs:14:5
+ |
+LL | foo();
+ | ^^^^^^
+ |
+ = note: this `Result` may be an `Err` variant, which should be handled
+
+error: unused `std::result::Result` in tuple element 0 that must be used
+ --> $DIR/must_use-tuple.rs:16:6
+ |
+LL | ((Err::<(), ()>(()), ()), ());
+ | ^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: this `Result` may be an `Err` variant, which should be handled
+
+error: aborting due to 5 previous errors
+