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warn on must_use use on async fn's

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This commit is contained in:
Gus Wynn 2021-10-06 13:19:39 -07:00
parent 495322d776
commit 958de5a938
3 changed files with 101 additions and 0 deletions
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32
compiler/rustc_passes/src/check_attr.rs
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@ -112,6 +112,7 @@ impl CheckAttrVisitor<'tcx> {
self.check_default_method_body_is_const(attr, span, target)
}
sym::must_not_suspend => self.check_must_not_suspend(&attr, span, target),
sym::must_use => self.check_must_use(hir_id, &attr, span, target),
sym::rustc_const_unstable
| sym::rustc_const_stable
| sym::unstable
@ -1046,6 +1047,37 @@ impl CheckAttrVisitor<'tcx> {
is_valid
}
/// Warns against some misuses of `#[must_use]`
fn check_must_use(
&self,
hir_id: HirId,
attr: &Attribute,
span: &Span,
_target: Target,
) -> bool {
let node = self.tcx.hir().get(hir_id);
if let Some(fn_node) = node.fn_kind() {
if let rustc_hir::IsAsync::Async = fn_node.asyncness() {
self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
lint.build(
"`must_use` attribute on `async` functions \
applies to the anonymous `Future` returned by the \
function, not the value within.",
)
.span_label(
*span,
"this attribute does nothing, the `Future`s \
returned by async functions are already `must_use`",
)
.emit();
});
}
}
// For now, its always valid
true
}
/// Checks if `#[must_not_suspend]` is applied to a function. Returns `true` if valid.
fn check_must_not_suspend(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
match target {