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use rustc_errors::DiagArgValue;
use super::prelude::*;
use crate::session_diagnostics::IllFormedAttributeInputLint;
pub(crate) struct MustUseParser;
impl<S: Stage> SingleAttributeParser<S> for MustUseParser {
const PATH: &[Symbol] = &[sym::must_use];
const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
Allow(Target::Fn),
Allow(Target::Enum),
Allow(Target::Struct),
Allow(Target::Union),
Allow(Target::Method(MethodKind::Trait { body: false })),
Allow(Target::Method(MethodKind::Trait { body: true })),
Allow(Target::Method(MethodKind::Inherent)),
Allow(Target::ForeignFn),
// `impl Trait` in return position can trip
// `unused_must_use` if `Trait` is marked as
// `#[must_use]`
Allow(Target::Trait),
Error(Target::WherePredicate),
]);
const TEMPLATE: AttributeTemplate = template!(
Word, NameValueStr: "reason",
"https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute"
);
fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
Some(AttributeKind::MustUse {
span: cx.attr_span,
reason: match args {
ArgParser::NoArgs => None,
ArgParser::NameValue(name_value) => {
let Some(value_str) = name_value.value_as_str() else {
cx.expected_string_literal(
name_value.value_span,
Some(&name_value.value_as_lit()),
);
return None;
};
Some(value_str)
}
ArgParser::List(_) => {
let suggestions = <Self as SingleAttributeParser<S>>::TEMPLATE
.suggestions(cx.attr_style, "must_use");
cx.emit_err(IllFormedAttributeInputLint {
num_suggestions: suggestions.len(),
suggestions: DiagArgValue::StrListSepByAnd(
suggestions.into_iter().map(|s| format!("`{s}`").into()).collect(),
),
span: cx.attr_span,
});
return None;
}
},
})
}
}
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