From 57488f79f80ca41343bcfc43ea3f29e9757619b2 Mon Sep 17 00:00:00 2001
From: Mahdi Ali-Raihan <asder8215@gmail.com>
Date: Fri, 22 May 2026 15:37:48 -0400
Subject: [PATCH] Add a clippy attribute #[clippy::no_dead_field_warning] to
 prevent certain types from propagating dead field warnings (e.g. PhantomData,
 PhantomPinned)

---
 clippy_lints/src/missing_fields_in_debug.rs |  7 +++++--
 clippy_lints/src/pub_underscore_fields.rs   |  5 +++--
 clippy_utils/src/attrs.rs                   | 15 +++++++++++++++
 clippy_utils/src/sym.rs                     |  1 +
 4 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/clippy_lints/src/missing_fields_in_debug.rs b/clippy_lints/src/missing_fields_in_debug.rs
index 332c19e140b3..27f4f1a1da9b 100644
--- a/clippy_lints/src/missing_fields_in_debug.rs
+++ b/clippy_lints/src/missing_fields_in_debug.rs
@@ -2,13 +2,13 @@ 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::visitors::{Visitable, for_each_expr};
+use clippy_utils::{is_clippy_no_dead_field_warning_attr, sym};
 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_lint::{LateContext, LateLintPass};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty::{Ty, TypeckResults};
 use rustc_session::declare_lint_pass;
 use rustc_span::{Span, Symbol};
@@ -185,6 +185,9 @@ 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 certain types (e.g. PhantomData, PhantomPinned) marked with
+                // this attribute
+                || is_clippy_no_dead_field_warning_attr(cx.sess(), cx.tcx, field.ty.basic_res())
             {
                 None
             } else {
diff --git a/clippy_lints/src/pub_underscore_fields.rs b/clippy_lints/src/pub_underscore_fields.rs
index 64724f7d01d0..4278070ecbfb 100644
--- a/clippy_lints/src/pub_underscore_fields.rs
+++ b/clippy_lints/src/pub_underscore_fields.rs
@@ -1,10 +1,10 @@
 use clippy_config::Conf;
 use clippy_config::types::PubUnderscoreFieldsBehaviour;
-use clippy_utils::attrs::is_doc_hidden;
+use clippy_utils::attrs::{is_clippy_no_dead_field_warning_attr, is_doc_hidden};
 use clippy_utils::diagnostics::span_lint_hir_and_then;
 use clippy_utils::res::{MaybeDef, MaybeResPath};
 use rustc_hir::{FieldDef, Item, ItemKind, LangItem};
-use rustc_lint::{LateContext, LateLintPass};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_session::impl_lint_pass;
 
 declare_clippy_lint! {
@@ -77,6 +77,7 @@ impl<'tcx> LateLintPass<'tcx> for PubUnderscoreFields {
                 && !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_clippy_no_dead_field_warning_attr(cx.sess(), cx.tcx, field.ty.basic_res())
             {
                 span_lint_hir_and_then(
                     cx,
diff --git a/clippy_utils/src/attrs.rs b/clippy_utils/src/attrs.rs
index 6e7434771369..30a6b812f39e 100644
--- a/clippy_utils/src/attrs.rs
+++ b/clippy_utils/src/attrs.rs
@@ -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;
@@ -91,6 +92,20 @@ pub fn is_doc_hidden(attrs: &[impl AttributeExt]) -> bool {
     attrs.iter().any(AttributeExt::is_doc_hidden)
 }
 
+/// Checks whether the original type is marked as `#[clippy::no_dead_field_warning]`
+pub fn is_clippy_no_dead_field_warning_attr(sess: &Session, tcx: TyCtxt<'_>, res: &Res) -> bool {
+    res.opt_def_id().is_some_and(|def_id| {
+        get_builtin_attr(
+            sess,
+            #[allow(deprecated)]
+            tcx.get_all_attrs(def_id),
+            sym::no_dead_field_warning,
+        )
+        .next()
+        .is_some()
+    })
+}
+
 /// 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/clippy_utils/src/sym.rs b/clippy_utils/src/sym.rs
index 6a7637fb1858..53e714563290 100644
--- a/clippy_utils/src/sym.rs
+++ b/clippy_utils/src/sym.rs
@@ -440,6 +440,7 @@ generate! {
     next_if_eq,
     next_multiple_of,
     next_tuple,
+    no_dead_field_warning,
     nth,
     ok,
     ok_or,