Port #[rustc_dummy]

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -240,6 +240,9 @@ pub enum AttributeKind {
     /// Represents [`#[doc]`](https://doc.rust-lang.org/stable/rustdoc/write-documentation/the-doc-attribute.html).
     DocComment { style: AttrStyle, kind: CommentKind, span: Span, comment: Symbol },
 
+    /// Represents `#[rustc_dummy]`.
+    Dummy,
+
     /// Represents [`#[export_name]`](https://doc.rust-lang.org/reference/abi.html#the-export_name-attribute).
     ExportName {
         /// The name to export this item with.

compiler/rustc_attr_data_structures/src/encode_cross_crate.rs

@@ -25,6 +25,7 @@ impl AttributeKind {
             ConstStabilityIndirect => No,
             Deprecation { .. } => Yes,
             DocComment { .. } => Yes,
+            Dummy => No,
             ExportName { .. } => Yes,
             Ignore { .. } => No,
             Inline(..) => No,

compiler/rustc_attr_parsing/src/attributes/dummy.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 DummyParser;
+impl<S: Stage> SingleAttributeParser<S> for DummyParser {
+    const PATH: &[Symbol] = &[sym::rustc_dummy];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepFirst;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Ignore;
+    const TEMPLATE: AttributeTemplate = template!(Word); // Anything, really
+
+    fn convert(_: &mut AcceptContext<'_, '_, S>, _: &ArgParser<'_>) -> Option<AttributeKind> {
+        Some(AttributeKind::Dummy)
+    }
+}

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -30,6 +30,7 @@ pub(crate) mod cfg;
 pub(crate) mod codegen_attrs;
 pub(crate) mod confusables;
 pub(crate) mod deprecation;
+pub(crate) mod dummy;
 pub(crate) mod inline;
 pub(crate) mod link_attrs;
 pub(crate) mod lint_helpers;

compiler/rustc_attr_parsing/src/context.rs

@@ -21,6 +21,7 @@ use crate::attributes::codegen_attrs::{
 };
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::deprecation::DeprecationParser;
+use crate::attributes::dummy::DummyParser;
 use crate::attributes::inline::{InlineParser, RustcForceInlineParser};
 use crate::attributes::link_attrs::{LinkNameParser, LinkSectionParser};
 use crate::attributes::lint_helpers::{AsPtrParser, PassByValueParser, PubTransparentParser};
@@ -127,6 +128,7 @@ attribute_parsers!(
 
         // tidy-alphabetical-start
         Single<DeprecationParser>,
+        Single<DummyParser>,
         Single<ExportNameParser>,
         Single<IgnoreParser>,
         Single<InlineParser>,

compiler/rustc_passes/src/check_attr.rs

@@ -207,7 +207,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 Attribute::Parsed(
                     AttributeKind::BodyStability { .. }
                     | AttributeKind::ConstStabilityIndirect
-                    | AttributeKind::MacroTransparency(_),
+                    | AttributeKind::MacroTransparency(_)
+                    | AttributeKind::Dummy,
                 ) => { /* do nothing  */ }
                 Attribute::Parsed(AttributeKind::AsPtr(attr_span)) => {
                     self.check_applied_to_fn_or_method(hir_id, *attr_span, span, target)