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

Author: asder8215

compiler/rustc_feature/src/builtin_attrs.rs

@@ -755,6 +755,9 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     rustc_attr!(rustc_force_inline,"`#[rustc_force_inline]` forces a free function to be inlined"),
     rustc_attr!(rustc_scalable_vector,"`#[rustc_scalable_vector]` defines a scalable vector type"),
+    rustc_attr!( rustc_marker_type, "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:

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -1604,6 +1604,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_main]`.
     RustcMain,
 
+    /// Represents `[#rustc_marker_type]`
+    RustcMarkerType,
+
     /// Represents `#[rustc_mir]`.
     RustcMir(ThinVec<RustcMirKind>),
 

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,
             RustcNeverReturnsNullPtr => Yes,

compiler/rustc_passes/src/check_attr.rs

@@ -334,6 +334,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::RustcLintUntrackedQueryInformation
                     | AttributeKind::RustcMacroTransparency(_)
                     | AttributeKind::RustcMain
+                    | AttributeKind::RustcMarkerType
                     | AttributeKind::RustcMir(_)
                     | AttributeKind::RustcNeverReturnsNullPtr
                     | AttributeKind::RustcNeverTypeOptions {..}

compiler/rustc_span/src/symbol.rs

@@ -1747,6 +1747,7 @@ symbols! {
         rustc_lint_untracked_query_information,
         rustc_macro_transparency,
         rustc_main,
+        rustc_marker_type,
         rustc_mir,
         rustc_must_implement_one_of,
         rustc_never_returns_null_ptr,

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")]

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::{is_marker_type, sym};
 use clippy_utils::visitors::{Visitable, for_each_expr};
 use rustc_ast::LitKind;
 use rustc_data_structures::fx::FxHashSet;
@@ -184,7 +184,8 @@ fn check_struct<'tcx>(
         .iter()
         .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
+                || is_marker_type(cx.tcx.hir_attrs(field.hir_id))
             {
                 None
             } else {

src/tools/clippy/clippy_lints/src/pub_underscore_fields.rs

@@ -70,13 +70,17 @@ impl<'tcx> LateLintPass<'tcx> for PubUnderscoreFields {
             },
         };
 
+        // These specific phantom language items do not need to trigger pub underscore field
+        // warnings
+        let phantom_types = [LangItem::PhantomData, LangItem::PhantomPinned];
+
         for field in variant_data.fields() {
             // Only pertains to fields that start with an underscore, and are public.
             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
+                && !is_marker_type(cx.tcx.hir_attrs(field.hir_id))
             {
                 span_lint_hir_and_then(
                     cx,

src/tools/clippy/clippy_utils/src/attrs.rs

@@ -91,6 +91,10 @@ pub fn is_doc_hidden(attrs: &[impl AttributeExt]) -> bool {
     attrs.iter().any(AttributeExt::is_doc_hidden)
 }
 
+pub fn is_marker_type(attrs: &[impl AttributeExt]) -> bool {
+    attrs.iter().any(AttributeExt::name? == sym::rustc_marker_type)
+}
+
 /// 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()

src/tools/clippy/tests/ui-toml/pub_underscore_fields/pub_underscore_fields.rs

@@ -6,6 +6,7 @@
 #![warn(clippy::pub_underscore_fields)]
 
 use std::marker::PhantomData;
+use std::marker::PhantonPinned;
 
 pub mod inner {
     use std::marker;
@@ -15,7 +16,8 @@ pub mod inner {
         pub _b: u8,
         //~^ pub_underscore_fields
         _c: i32,
-        pub _mark: marker::PhantomData<u8>,
+        pub _mark_pinned: marker::PhantomPinned, 
+        pub _mark_data: marker::PhantomData<u8>,
     }
 
     mod inner2 {
@@ -68,7 +70,8 @@ fn main() {
     pub struct NamedPub {
         r#pub: bool,
         _pub: String,
-        pub(crate) _mark: PhantomData<u8>,
+        pub _mark_pinned: marker::PhantomPinned, 
+        pub _mark_data: marker::PhantomData<u8>,
     }
 
     // shouldn't warn when `#[allow]` is used on field level