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rustc_marker_type built in attribute created to have certain marker types not trigger dead code warnings from clippy #154978

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rustc_marker_type built in attribute created to have certain marker types not trigger dead code warnings from clippy #154978

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12 changes: 12 additions & 0 deletions compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs
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Expand Up @@ -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),
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@asder8215 asder8215 Apr 14, 2026 •
edited by rustbot
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View changes since the review

Added that the attribute can be applied to enums and type aliases. I wasn't sure how to go about testing it in the rustc's tests/ui; it's not giving me warning when I do something similar in clippy_lints like:

struct S {
    unused_field: i32,
}

impl fmt::Debug for S5 {
    //~ WARN unused field
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("S")
            .finish()
    }
}

Is this something I would have to test for only on the clippy side of things?

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];
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1 change: 1 addition & 0 deletions compiler/rustc_attr_parsing/src/context.rs
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Expand Up @@ -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>>,
Expand Down
5 changes: 5 additions & 0 deletions compiler/rustc_feature/src/builtin_attrs.rs
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Expand Up @@ -955,6 +955,11 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
rustc_must_match_exhaustively,
"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,
"`#[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:
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3 changes: 3 additions & 0 deletions compiler/rustc_hir/src/attrs/data_structures.rs
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Expand Up @@ -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,

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1 change: 1 addition & 0 deletions compiler/rustc_hir/src/attrs/encode_cross_crate.rs
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Expand Up @@ -161,6 +161,7 @@ impl AttributeKind {
RustcMustMatchExhaustively(..) => Yes,
RustcNeverReturnsNullPtr => Yes,
RustcNeverTypeOptions { .. } => No,
RustcNoDeadCodeWarning => Yes,
RustcNoImplicitAutorefs => Yes,
RustcNoImplicitBounds => No,
RustcNoMirInline => Yes,
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1 change: 1 addition & 0 deletions compiler/rustc_passes/src/check_attr.rs
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Expand Up @@ -348,6 +348,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
| AttributeKind::RustcMustMatchExhaustively(..)
| AttributeKind::RustcNeverReturnsNullPtr
| AttributeKind::RustcNeverTypeOptions {..}
| AttributeKind::RustcNoDeadCodeWarning
| AttributeKind::RustcNoImplicitAutorefs
| AttributeKind::RustcNoImplicitBounds
| AttributeKind::RustcNoMirInline
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1 change: 1 addition & 0 deletions compiler/rustc_span/src/symbol.rs
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Expand Up @@ -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,
Expand Down
2 changes: 2 additions & 0 deletions library/core/src/marker.rs
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Expand Up @@ -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")]
Expand Down Expand Up @@ -1023,6 +1024,7 @@ 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")]
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7 changes: 4 additions & 3 deletions src/tools/clippy/clippy_lints/src/missing_fields_in_debug.rs
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Expand Up @@ -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;
Expand Down Expand Up @@ -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 {
Expand Down
8 changes: 4 additions & 4 deletions src/tools/clippy/clippy_lints/src/pub_underscore_fields.rs
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@@ -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;

Expand Down Expand Up @@ -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,
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6 changes: 6 additions & 0 deletions src/tools/clippy/clippy_utils/src/attrs.rs
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Expand Up @@ -4,6 +4,7 @@ use crate::source::SpanRangeExt;
use crate::{sym, tokenize_with_text};
use rustc_ast::attr::AttributeExt;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::find_attr;
use rustc_lexer::TokenKind;
use rustc_lint::LateContext;
Expand Down Expand Up @@ -91,6 +92,11 @@ pub fn is_doc_hidden(attrs: &[impl AttributeExt]) -> bool {
attrs.iter().any(AttributeExt::is_doc_hidden)
}

/// Checks whether the original type is marked as `#[rustc_no_dead_code_warning]`
pub fn is_rustc_no_dead_code_warning_attr(tcx: TyCtxt<'_>, res: &Res) -> bool {
res.opt_def_id().map(|def_id| find_attr!(tcx, def_id, RustcNoDeadCodeWarning)).unwrap_or(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()
Expand Down
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