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`

6 files changed, 33 insertions, 3 deletions

diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
index 9ebf4c1793d..066e3e9eceb 100644
--- a/compiler/rustc_attr_data_structures/src/attributes.rs
+++ b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -233,8 +233,13 @@ pub enum AttributeKind {
 
     /// Represents `#[rustc_macro_transparency]`.
     MacroTransparency(Transparency),
+
+    /// Represents [`#[may_dangle]`](https://std-dev-guide.rust-lang.org/tricky/may-dangle.html).
+    MayDangle(Span),
+
     /// Represents `#[optimize(size|speed)]`
     Optimize(OptimizeAttr, Span),
+
     /// Represents [`#[repr]`](https://doc.rust-lang.org/stable/reference/type-layout.html#representations).
     Repr(ThinVec<(ReprAttr, Span)>),
 
diff --git a/compiler/rustc_attr_parsing/src/attributes/mod.rs b/compiler/rustc_attr_parsing/src/attributes/mod.rs
index 78a696afa27..1bb5edba326 100644
--- a/compiler/rustc_attr_parsing/src/attributes/mod.rs
+++ b/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;
diff --git a/compiler/rustc_attr_parsing/src/attributes/semantics.rs b/compiler/rustc_attr_parsing/src/attributes/semantics.rs
new file mode 100644
index 00000000000..071574a5612
--- /dev/null
+++ b/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))
+    }
+}
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index 8311fccacd8..1bcf500459d 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/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>,
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 556f50a85af..1a526d5bce0 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -1302,6 +1302,7 @@ impl AttributeExt for Attribute {
             // FIXME: should not be needed anymore when all attrs are parsed
             Attribute::Parsed(AttributeKind::Deprecation { span, .. }) => *span,
             Attribute::Parsed(AttributeKind::DocComment { span, .. }) => *span,
+            Attribute::Parsed(AttributeKind::MayDangle(span)) => *span,
             a => panic!("can't get the span of an arbitrary parsed attribute: {a:?}"),
         }
     }
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 5fb9514e5ca..d0630383477 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -163,6 +163,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 Attribute::Parsed(AttributeKind::AsPtr(attr_span)) => {
                     self.check_applied_to_fn_or_method(hir_id, *attr_span, span, target)
                 }
+                &Attribute::Parsed(AttributeKind::MayDangle(attr_span)) => {
+                    self.check_may_dangle(hir_id, attr_span)
+                }
                 Attribute::Unparsed(_) => {
                     match attr.path().as_slice() {
                         [sym::diagnostic, sym::do_not_recommend, ..] => {
@@ -236,7 +239,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         [sym::collapse_debuginfo, ..] => self.check_collapse_debuginfo(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, target),
-                        [sym::may_dangle, ..] => self.check_may_dangle(hir_id, attr),
                         [sym::rustc_pass_by_value, ..] => self.check_pass_by_value(attr, span, target),
                         [sym::rustc_allow_incoherent_impl, ..] => {
                             self.check_allow_incoherent_impl(attr, span, target)
@@ -1619,7 +1621,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     }
 
     /// Checks if `#[may_dangle]` is applied to a lifetime or type generic parameter in `Drop` impl.
-    fn check_may_dangle(&self, hir_id: HirId, attr: &Attribute) {
+    fn check_may_dangle(&self, hir_id: HirId, attr_span: Span) {
         if let hir::Node::GenericParam(param) = self.tcx.hir_node(hir_id)
             && matches!(
                 param.kind,
@@ -1636,7 +1638,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             return;
         }
 
-        self.dcx().emit_err(errors::InvalidMayDangle { attr_span: attr.span() });
+        self.dcx().emit_err(errors::InvalidMayDangle { attr_span });
     }
 
     /// Checks if `#[cold]` is applied to a non-function.