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

Author: asder8215

compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs

@@ -14,6 +14,18 @@ impl<S: Stage> NoArgsAttributeParser<S> for RustcAsPtrParser {
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcAsPtr;
 }
 
+pub(crate) struct RustcNoDeadCodeWarningParser;
+impl<S: Stage> NoArgsAttributeParser<S> for RustcNoDeadCodeWarningParser {
+    const PATH: &[Symbol] = &[sym::rustc_no_dead_code_warning];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Struct),
+        Allow(Target::Enum),
+        Allow(Target::TyAlias),
+    ]);
+    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNoDeadCodeWarning;
+}
+
 pub(crate) struct RustcPubTransparentParser;
 impl<S: Stage> NoArgsAttributeParser<S> for RustcPubTransparentParser {
     const PATH: &[Symbol] = &[sym::rustc_pub_transparent];

compiler/rustc_attr_parsing/src/context.rs

@@ -312,6 +312,7 @@ attribute_parsers!(
         Single<WithoutArgs<RustcLintUntrackedQueryInformationParser>>,
         Single<WithoutArgs<RustcMainParser>>,
         Single<WithoutArgs<RustcNeverReturnsNullPtrParser>>,
+        Single<WithoutArgs<RustcNoDeadCodeWarningParser>>,
         Single<WithoutArgs<RustcNoImplicitAutorefsParser>>,
         Single<WithoutArgs<RustcNoImplicitBoundsParser>>,
         Single<WithoutArgs<RustcNoMirInlineParser>>,

compiler/rustc_feature/src/builtin_attrs.rs

@@ -1424,6 +1424,11 @@ 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_no_dead_code_warning, Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::Yes,
+        "`#[rustc_no_dead_code_warning]` attribute is used to mark certain types that do not need \
+        to propagate dead code warnings as field members in other types"
+    ),
 
     // ==========================================================================
     // Internal attributes, Testing:

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -1502,6 +1502,9 @@ pub enum AttributeKind {
         diverging_block_default: Option<DivergingBlockBehavior>,
     },
 
+    /// Represents `#[rustc_no_dead_code_warning]`
+    RustcNoDeadCodeWarning,
+
     /// Represents `#[rustc_no_implicit_autorefs]`
     RustcNoImplicitAutorefs,
 

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -161,6 +161,7 @@ impl AttributeKind {
             RustcMustMatchExhaustively(..) => Yes,
             RustcNeverReturnsNullPtr => Yes,
             RustcNeverTypeOptions { .. } => No,
+            RustcNoDeadCodeWarning => Yes,
             RustcNoImplicitAutorefs => Yes,
             RustcNoImplicitBounds => No,
             RustcNoMirInline => Yes,

compiler/rustc_passes/src/check_attr.rs

@@ -351,6 +351,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::RustcMustMatchExhaustively(..)
                     | AttributeKind::RustcNeverReturnsNullPtr
                     | AttributeKind::RustcNeverTypeOptions {..}
+                    | AttributeKind::RustcNoDeadCodeWarning
                     | AttributeKind::RustcNoImplicitAutorefs
                     | AttributeKind::RustcNoImplicitBounds
                     | AttributeKind::RustcNoMirInline

compiler/rustc_span/src/symbol.rs

@@ -1765,6 +1765,7 @@ symbols! {
         rustc_must_match_exhaustively,
         rustc_never_returns_null_ptr,
         rustc_never_type_options,
+        rustc_no_dead_code_warning,
         rustc_no_implicit_autorefs,
         rustc_no_implicit_bounds,
         rustc_no_mir_inline,

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_no_dead_code_warning]
 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_no_dead_code_warning]
 pub struct PhantomPinned;
 
 #[stable(feature = "pin", since = "1.33.0")]

src/tools/clippy/clippy_lints/src/missing_fields_in_debug.rs

@@ -2,12 +2,12 @@ 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_rustc_no_dead_code_warning_attr, sym};
 use clippy_utils::visitors::{Visitable, for_each_expr};
 use rustc_ast::LitKind;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::{Block, Expr, ExprKind, Impl, Item, ItemKind, LangItem, Node, QPath, TyKind, VariantData};
+use rustc_hir::{Block, Expr, ExprKind, Impl, Item, ItemKind, Node, QPath, TyKind, VariantData};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::{Ty, TypeckResults};
 use rustc_session::declare_lint_pass;
@@ -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)
+                || is_rustc_no_dead_code_warning_attr(cx.tcx, field.ty.basic_res())
+                // We exclude certain types (e.g. PhantomData, PhantomPinned) marked with
             {
                 None
             } else {

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, is_rustc_no_dead_code_warning_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;
 
@@ -76,7 +76,7 @@ impl<'tcx> LateLintPass<'tcx> for PubUnderscoreFields {
                 // 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)
+                && !is_rustc_no_dead_code_warning_attr(cx.tcx, field.ty.basic_res())
             {
                 span_lint_hir_and_then(
                     cx,