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Add unstable #[may_ignore] attribute to cancel #[must_use] #79572

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3 changes: 3 additions & 0 deletions compiler/rustc_feature/src/active.rs
Original file line number Diff line number Diff line change
@@ -620,6 +620,9 @@ declare_features! (
/// Allows capturing disjoint fields in a closure/generator (RFC 2229).
(active, capture_disjoint_fields, "1.49.0", Some(53488), None),

/// Allow `#[may_ignore]` attribute.
(active, may_ignore, "1.50.0", Some(99999999), None),
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// TODO: This still needs a real tracking issue.


// -------------------------------------------------------------------------
// feature-group-end: actual feature gates
// -------------------------------------------------------------------------
1 change: 1 addition & 0 deletions compiler/rustc_feature/src/builtin_attrs.rs
Original file line number Diff line number Diff line change
@@ -207,6 +207,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
ungated!(forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
ungated!(deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
ungated!(must_use, AssumedUsed, template!(Word, NameValueStr: "reason")),
gated!(may_ignore, AssumedUsed, template!(Word), experimental!(may_ignore)),
// FIXME(#14407)
ungated!(
deprecated, Normal,
20 changes: 15 additions & 5 deletions compiler/rustc_lint/src/unused.rs
Original file line number Diff line number Diff line change
@@ -101,11 +101,6 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
return;
}

let ty = cx.typeck_results().expr_ty(&expr);
let type_permits_lack_of_use = check_must_use_ty(cx, ty, &expr, s.span, "", "", 1);

let mut fn_warned = false;
let mut op_warned = false;
let maybe_def_id = match expr.kind {
hir::ExprKind::Call(ref callee, _) => {
match callee.kind {
@@ -123,6 +118,21 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
hir::ExprKind::MethodCall(..) => cx.typeck_results().type_dependent_def_id(expr.hir_id),
_ => None,
};

if let Some(def_id) = maybe_def_id {
for attr in cx.tcx.get_attrs(def_id).iter() {
if cx.sess().check_name(attr, sym::may_ignore) {
// Don't warn if the function was marked as #[may_ignore].
return;
}
}
}

let ty = cx.typeck_results().expr_ty(&expr);
let type_permits_lack_of_use = check_must_use_ty(cx, ty, &expr, s.span, "", "", 1);

let mut fn_warned = false;
let mut op_warned = false;
if let Some(def_id) = maybe_def_id {
fn_warned = check_must_use_def(cx, def_id, s.span, "return value of ", "");
} else if type_permits_lack_of_use {
1 change: 1 addition & 0 deletions compiler/rustc_span/src/symbol.rs
Original file line number Diff line number Diff line change
@@ -681,6 +681,7 @@ symbols! {
maxnumf32,
maxnumf64,
may_dangle,
may_ignore,
maybe_uninit,
maybe_uninit_uninit,
maybe_uninit_zeroed,
4 changes: 4 additions & 0 deletions src/test/ui/feature-gate-may_ignore.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
#[may_ignore]
//~^ ERROR the `#[may_ignore]` attribute is an experimental feature [E0658]
fn main() {
}
12 changes: 12 additions & 0 deletions src/test/ui/feature-gate-may_ignore.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
error[E0658]: the `#[may_ignore]` attribute is an experimental feature
--> $DIR/feature-gate-may_ignore.rs:1:1
|
LL | #[may_ignore]
| ^^^^^^^^^^^^^
|
= note: see issue #99999999 <https://github.com/rust-lang/rust/issues/99999999> for more information
= help: add `#![feature(may_ignore)]` to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.
18 changes: 18 additions & 0 deletions src/test/ui/may_ignore.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
// check-pass

#![feature(may_ignore)]
#![warn(unused_must_use)]

fn warn() -> Result<i32, i32> {
Err(1)
}

#[may_ignore]
fn no_warn() -> Result<i32, i32> {
Err(2)
}

fn main() {
warn(); //~ WARN [unused_must_use]
no_warn();
}
15 changes: 15 additions & 0 deletions src/test/ui/may_ignore.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
warning: unused `std::result::Result` that must be used
--> $DIR/may_ignore.rs:16:5
|
LL | warn();
| ^^^^^^^
|
note: the lint level is defined here
--> $DIR/may_ignore.rs:4:9
|
LL | #![warn(unused_must_use)]
| ^^^^^^^^^^^^^^^
= note: this `Result` may be an `Err` variant, which should be handled

warning: 1 warning emitted