Port #[must_use] to new attribute parsing infrastructure

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -33,6 +33,7 @@ pub(crate) mod confusables;
 pub(crate) mod deprecation;
 pub(crate) mod inline;
 pub(crate) mod lint_helpers;
+pub(crate) mod must_use;
 pub(crate) mod repr;
 pub(crate) mod semantics;
 pub(crate) mod stability;

compiler/rustc_attr_parsing/src/attributes/must_use.rs

@@ -0,0 +1,40 @@
+use rustc_attr_data_structures::AttributeKind;
+use rustc_errors::DiagArgValue;
+use rustc_feature::{AttributeTemplate, template};
+use rustc_span::{Symbol, sym};
+
+use crate::attributes::{AttributeOrder, OnDuplicate, SingleAttributeParser};
+use crate::context::{AcceptContext, Stage};
+use crate::parser::ArgParser;
+use crate::session_diagnostics;
+
+pub(crate) struct MustUseParser;
+
+impl<S: Stage> SingleAttributeParser<S> for MustUseParser {
+    const PATH: &[Symbol] = &[sym::must_use];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepLast;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
+    const TEMPLATE: AttributeTemplate = template!(Word, NameValueStr: "reason");
+
+    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) => name_value.value_as_str(),
+                ArgParser::List(_) => {
+                    let suggestions =
+                        <Self as SingleAttributeParser<S>>::TEMPLATE.suggestions(false, "must_use");
+                    cx.emit_err(session_diagnostics::MustUseIllFormedAttributeInput {
+                        num_suggestions: suggestions.len(),
+                        suggestions: DiagArgValue::StrListSepByAnd(
+                            suggestions.into_iter().map(|s| format!("`{s}`").into()).collect(),
+                        ),
+                        span: cx.attr_span,
+                    });
+                    return None;
+                }
+            },
+        })
+    }
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -20,6 +20,7 @@ use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::deprecation::DeprecationParser;
 use crate::attributes::inline::{InlineParser, RustcForceInlineParser};
 use crate::attributes::lint_helpers::{AsPtrParser, PubTransparentParser};
+use crate::attributes::must_use::MustUseParser;
 use crate::attributes::repr::{AlignParser, ReprParser};
 use crate::attributes::semantics::MayDangleParser;
 use crate::attributes::stability::{
@@ -112,6 +113,7 @@ attribute_parsers!(
         Single<DeprecationParser>,
         Single<InlineParser>,
         Single<MayDangleParser>,
+        Single<MustUseParser>,
         Single<OptimizeParser>,
         Single<PubTransparentParser>,
         Single<RustcForceInlineParser>,

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -436,6 +436,15 @@ pub(crate) struct IllFormedAttributeInput {
     pub suggestions: DiagArgValue,
 }
 
+#[derive(Diagnostic)]
+#[diag(attr_parsing_ill_formed_attribute_input)]
+pub(crate) struct MustUseIllFormedAttributeInput {
+    #[primary_span]
+    pub span: Span,
+    pub num_suggestions: usize,
+    pub suggestions: DiagArgValue,
+}
+
 #[derive(Diagnostic)]
 #[diag(attr_parsing_stability_outside_std, code = E0734)]
 pub(crate) struct StabilityOutsideStd {