rustc_marker_type built in attribute created to have certain marker types not trigger dead code warnings from clippy

asder8215 · asder8215 · commit 9f0d57d1ec22 · 2026-04-10T16:01:07.000-04:00
diff --git a/compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs b/compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs
@@ -14,6 +14,15 @@ impl<S: Stage> NoArgsAttributeParser<S> for RustcAsPtrParser {
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcAsPtr;
 }
 
+pub(crate) struct RustcMarkerTypeParser;
+impl<S: Stage> NoArgsAttributeParser<S> for RustcMarkerTypeParser {
+    const PATH: &[Symbol] = &[sym::rustc_marker_type];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
+    const CREATE: fn(Span) -> AttributeKind =
+        |span| AttributeKind::RustcMarkerType(sym::rustc_marker_type, span);
+}
+
 pub(crate) struct RustcPubTransparentParser;
 impl<S: Stage> NoArgsAttributeParser<S> for RustcPubTransparentParser {
     const PATH: &[Symbol] = &[sym::rustc_pub_transparent];
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
@@ -308,6 +308,7 @@ attribute_parsers!(
         Single<WithoutArgs<RustcLintQueryInstabilityParser>>,
         Single<WithoutArgs<RustcLintUntrackedQueryInformationParser>>,
         Single<WithoutArgs<RustcMainParser>>,
+        Single<WithoutArgs<RustcMarkerTypeParser>>,
         Single<WithoutArgs<RustcNeverReturnsNullPtrParser>>,
         Single<WithoutArgs<RustcNoImplicitAutorefsParser>>,
         Single<WithoutArgs<RustcNoImplicitBoundsParser>>,
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -1418,6 +1418,11 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_must_match_exhaustively, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::Yes,
         "enums with `#[rustc_must_match_exhaustively]` must be matched on with a match block that mentions all variants explicitly"
     ),
+    rustc_attr!(
+        rustc_marker_type, Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::Yes,
+        "the `#[rustc_marker_type]` attribute is used by the standard library to mark certain marker types \
+        that do not need dead code warnings"
+    ),
 
     // ==========================================================================
     // Internal attributes, Testing:
diff --git a/compiler/rustc_hir/src/attrs/data_structures.rs b/compiler/rustc_hir/src/attrs/data_structures.rs
@@ -1465,6 +1465,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_main]`.
     RustcMain,
 
+    /// Represents `#[rustc_marker_type]`
+    RustcMarkerType(Symbol, Span),
+
     /// Represents `#[rustc_mir]`.
     RustcMir(ThinVec<RustcMirKind>),
 
diff --git a/compiler/rustc_hir/src/attrs/encode_cross_crate.rs b/compiler/rustc_hir/src/attrs/encode_cross_crate.rs
@@ -155,6 +155,7 @@ impl AttributeKind {
             RustcLintUntrackedQueryInformation => Yes,
             RustcMacroTransparency(..) => Yes,
             RustcMain => No,
+            RustcMarkerType(..) => Yes,
             RustcMir(..) => Yes,
             RustcMustImplementOneOf { .. } => No,
             RustcMustMatchExhaustively(..) => Yes,
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
@@ -339,6 +339,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::RustcLintUntrackedQueryInformation
                     | AttributeKind::RustcMacroTransparency(_)
                     | AttributeKind::RustcMain
+                    | AttributeKind::RustcMarkerType(..)
                     | AttributeKind::RustcMir(_)
                     | AttributeKind::RustcMustMatchExhaustively(..)
                     | AttributeKind::RustcNeverReturnsNullPtr
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
@@ -1753,6 +1753,7 @@ symbols! {
         rustc_lint_untracked_query_information,
         rustc_macro_transparency,
         rustc_main,
+        rustc_marker_type,
         rustc_mir,
         rustc_must_implement_one_of,
         rustc_must_match_exhaustively,
diff --git a/library/core/src/marker.rs b/library/core/src/marker.rs
@@ -808,6 +808,7 @@ impl<T: PointeeSized> !Sync for *mut T {}
 /// [drop check]: Drop#drop-check
 #[lang = "phantom_data"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_marker_type]
 pub struct PhantomData<T: PointeeSized>;
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1021,6 +1022,7 @@ pub auto trait Unpin {}
 // will likely eventually be deprecated, and all new code should be using `UnsafePinned` instead.
 #[stable(feature = "pin", since = "1.33.0")]
 #[derive(Debug, Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[rustc_marker_type]
 pub struct PhantomPinned;
 
 #[stable(feature = "pin", since = "1.33.0")]
diff --git a/src/tools/clippy/clippy_lints/src/missing_fields_in_debug.rs b/src/tools/clippy/clippy_lints/src/missing_fields_in_debug.rs
@@ -2,7 +2,7 @@ use std::ops::ControlFlow;
 
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::res::{MaybeDef, MaybeResPath};
-use clippy_utils::sym;
+use clippy_utils::{has_rustc_marker_type_attr, sym};
 use clippy_utils::visitors::{Visitable, for_each_expr};
 use rustc_ast::LitKind;
 use rustc_data_structures::fx::FxHashSet;
@@ -185,6 +185,8 @@ fn check_struct<'tcx>(
         .filter_map(|field| {
             if field_accesses.contains(&field.ident.name)
                 || field.ty.basic_res().is_lang_item(cx, LangItem::PhantomData)
+                // We exclude marker types (e.g. PhantomData, PhantomPinned) from emitting warnings
+                || has_rustc_marker_type_attr(cx.tcx, field.ty.basic_res())
             {
                 None
             } else {
diff --git a/src/tools/clippy/clippy_lints/src/pub_underscore_fields.rs b/src/tools/clippy/clippy_lints/src/pub_underscore_fields.rs
@@ -1,9 +1,9 @@
 use clippy_config::Conf;
 use clippy_config::types::PubUnderscoreFieldsBehaviour;
-use clippy_utils::attrs::is_doc_hidden;
+use clippy_utils::attrs::{is_doc_hidden, has_rustc_marker_type_attr};
 use clippy_utils::diagnostics::span_lint_hir_and_then;
-use clippy_utils::res::{MaybeDef, MaybeResPath};
-use rustc_hir::{FieldDef, Item, ItemKind, LangItem};
+use clippy_utils::res::MaybeResPath;
+use rustc_hir::{FieldDef, Item, ItemKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::impl_lint_pass;
 
@@ -75,8 +75,8 @@ impl<'tcx> LateLintPass<'tcx> for PubUnderscoreFields {
             if field.ident.as_str().starts_with('_') && is_visible(field)
                 // We ignore fields that have `#[doc(hidden)]`.
                 && !is_doc_hidden(cx.tcx.hir_attrs(field.hir_id))
-                // We ignore fields that are `PhantomData`.
-                && !field.ty.basic_res().is_lang_item(cx, LangItem::PhantomData)
+                // We exclude marker types (e.g. PhantomData, PhantomPinned) from emitting warnings.
+                && !has_rustc_marker_type_attr(cx.tcx, field.ty.basic_res())
             {
                 span_lint_hir_and_then(
                     cx,
diff --git a/src/tools/clippy/clippy_utils/src/attrs.rs b/src/tools/clippy/clippy_utils/src/attrs.rs
@@ -4,7 +4,8 @@ use crate::source::SpanRangeExt;
 use crate::{sym, tokenize_with_text};
 use rustc_ast::attr::AttributeExt;
 use rustc_errors::Applicability;
-use rustc_hir::find_attr;
+use rustc_hir::def::Res;
+use rustc_hir::{find_attr};
 use rustc_lexer::TokenKind;
 use rustc_lint::LateContext;
 use rustc_middle::ty::{AdtDef, TyCtxt};
@@ -91,6 +92,15 @@ pub fn is_doc_hidden(attrs: &[impl AttributeExt]) -> bool {
     attrs.iter().any(AttributeExt::is_doc_hidden)
 }
 
+/// Checks whether a given result of a name resolution are marked as `#[rustc_marker_type]`
+pub fn has_rustc_marker_type_attr(tcx: TyCtxt<'_>, res: &Res) -> bool {
+    if let Res::Def(_, def_id) = res {
+        find_attr!(tcx, *def_id, RustcMarkerType(..))
+    } else {
+        false
+    }
+}
+
 /// Checks whether the given ADT, or any of its fields/variants, are marked as `#[non_exhaustive]`
 pub fn has_non_exhaustive_attr(tcx: TyCtxt<'_>, adt: AdtDef<'_>) -> bool {
     adt.is_variant_list_non_exhaustive()
diff --git a/src/tools/clippy/tests/ui-toml/pub_underscore_fields/pub_underscore_fields.all_pub_fields.stderr b/src/tools/clippy/tests/ui-toml/pub_underscore_fields/pub_underscore_fields.all_pub_fields.stderr
@@ -1,5 +1,5 @@
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:15:9
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:13:9
    |
 LL |         pub _b: u8,
    |         ^^^^^^
@@ -9,47 +9,47 @@ LL |         pub _b: u8,
    = help: to override `-D warnings` add `#[allow(clippy::pub_underscore_fields)]`
 
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:24:13
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:23:13
    |
 LL |             pub(in crate::inner) _f: Option<()>,
    |             ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider removing the underscore, or making the field private
 
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:29:13
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:28:13
    |
 LL |             pub _g: String,
    |             ^^^^^^
    |
    = help: consider removing the underscore, or making the field private
 
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:37:9
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:36:9
    |
 LL |         pub _a: usize,
    |         ^^^^^^
    |
    = help: consider removing the underscore, or making the field private
 
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:45:9
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:44:9
    |
 LL |         pub _c: i64,
    |         ^^^^^^
    |
    = help: consider removing the underscore, or making the field private
 
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:49:9
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:48:9
    |
 LL |         pub _e: Option<u8>,
    |         ^^^^^^
    |
    = help: consider removing the underscore, or making the field private
 
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:63:9
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:62:9
    |
 LL |         pub(crate) _b: Option<String>,
    |         ^^^^^^^^^^^^^
diff --git a/src/tools/clippy/tests/ui-toml/pub_underscore_fields/pub_underscore_fields.exported.stderr b/src/tools/clippy/tests/ui-toml/pub_underscore_fields/pub_underscore_fields.exported.stderr
@@ -1,5 +1,5 @@
 error: field marked as public but also inferred as unused because it's prefixed with `_`
-  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:15:9
+  --> tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs:13:9
    |
 LL |         pub _b: u8,
    |         ^^^^^^
diff --git a/src/tools/clippy/tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs b/src/tools/clippy/tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs
@@ -5,17 +5,16 @@
 #![allow(unused)]
 #![warn(clippy::pub_underscore_fields)]
 
-use std::marker::PhantomData;
 
 pub mod inner {
-    use std::marker;
 
     pub struct PubSuper {
         pub(super) a: usize,
         pub _b: u8,
         //~^ pub_underscore_fields
         _c: i32,
-        pub _mark: marker::PhantomData<u8>,
+        pub _mark_pinned: std::marker::PhantomPinned, 
+        pub _mark_data: std::marker::PhantomData<u8>,
     }
 
     mod inner2 {
@@ -68,7 +67,8 @@ fn main() {
     pub struct NamedPub {
         r#pub: bool,
         _pub: String,
-        pub(crate) _mark: PhantomData<u8>,
+        pub _mark_pinned: std::marker::PhantomPinned, 
+        pub _mark_data: std::marker::PhantomData<u8>,
     }
 
     // shouldn't warn when `#[allow]` is used on field level
diff --git a/src/tools/clippy/tests/ui/missing_fields_in_debug.rs b/src/tools/clippy/tests/ui/missing_fields_in_debug.rs
@@ -2,7 +2,7 @@
 #![warn(clippy::missing_fields_in_debug)]
 
 use std::fmt;
-use std::marker::PhantomData;
+use std::marker::{PhantomData, PhantomPinned};
 use std::ops::Deref;
 use std::thread::LocalKey;
 
@@ -179,16 +179,17 @@ mod comment1175473620 {
 }
 
 // https://github.com/rust-lang/rust-clippy/pull/10616#discussion_r1175488757
-// PhantomData is an exception and does not need to be included
-struct WithPD {
+// PhantomData and PhantomPinned are exceptions and do not need to be included
+struct WithPDPP {
     a: u8,
     b: u8,
-    c: PhantomData<String>,
+    c: PhantomPinned,
+    d: PhantomData<String>,
 }
 
-impl fmt::Debug for WithPD {
+impl fmt::Debug for WithPDPP {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("WithPD")
+        f.debug_struct("WithPDPP")
             .field("a", &self.a)
             .field("b", &self.b)
             .finish()
