Rollup merge of #142539 - GrigorenkoPV:attributes/may_dangle, r=jdonszelmann

Port `#[may_dangle]` to the new attribute system

Very similar to rust-lang/rust#142498.

This is a part of rust-lang/rust#131229, so
r? `@jdonszelmann`

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -34,6 +34,7 @@ pub(crate) mod deprecation;
 pub(crate) mod inline;
 pub(crate) mod lint_helpers;
 pub(crate) mod repr;
+pub(crate) mod semantics;
 pub(crate) mod stability;
 pub(crate) mod transparency;
 pub(crate) mod util;

compiler/rustc_attr_parsing/src/attributes/semantics.rs

@@ -0,0 +1,19 @@
+use rustc_attr_data_structures::AttributeKind;
+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;
+
+pub(crate) struct MayDangleParser;
+impl<S: Stage> SingleAttributeParser<S> for MayDangleParser {
+    const PATH: &[Symbol] = &[sym::may_dangle];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepFirst;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const TEMPLATE: AttributeTemplate = template!(Word);
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, _args: &ArgParser<'_>) -> Option<AttributeKind> {
+        Some(AttributeKind::MayDangle(cx.attr_span))
+    }
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -21,6 +21,7 @@ use crate::attributes::deprecation::DeprecationParser;
 use crate::attributes::inline::{InlineParser, RustcForceInlineParser};
 use crate::attributes::lint_helpers::AsPtrParser;
 use crate::attributes::repr::{AlignParser, ReprParser};
+use crate::attributes::semantics::MayDangleParser;
 use crate::attributes::stability::{
     BodyStabilityParser, ConstStabilityIndirectParser, ConstStabilityParser, StabilityParser,
 };
@@ -110,6 +111,7 @@ attribute_parsers!(
         Single<ConstStabilityIndirectParser>,
         Single<DeprecationParser>,
         Single<InlineParser>,
+        Single<MayDangleParser>,
         Single<OptimizeParser>,
         Single<RustcForceInlineParser>,
         Single<TransparencyParser>,