clippy built in attribute created to have certain marker types not trigger dead code warnings as field members from other structs

Author: asder8215

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")]
+#[clippy::no_dead_code_warning]
 pub struct PhantomData<T: PointeeSized>;
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -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)]
+#[clippy::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

@@ -2,13 +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::{is_clippy_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_lint::{LateContext, LateLintPass};
+use rustc_hir::{Block, Expr, ExprKind, Impl, Item, ItemKind, Node, QPath, TyKind, VariantData};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty::{Ty, TypeckResults};
 use rustc_session::declare_lint_pass;
 use rustc_span::{Span, Symbol};
@@ -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 certain types (e.g. PhantomData, PhantomPinned) marked with
+                || is_clippy_no_dead_code_warning_attr(cx.sess(), cx.tcx, field.ty.basic_res())
             {
                 None
             } else {

src/tools/clippy/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_doc_hidden, is_clippy_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 rustc_lint::{LateContext, LateLintPass};
+use clippy_utils::res::{MaybeResPath};
+use rustc_hir::{FieldDef, Item, ItemKind};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_session::impl_lint_pass;
 
 declare_clippy_lint! {
@@ -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_clippy_no_dead_code_warning_attr(cx.sess(), cx.tcx, field.ty.basic_res())
             {
                 span_lint_hir_and_then(
                     cx,

src/tools/clippy/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;
@@ -35,6 +36,7 @@ pub fn get_builtin_attr<'a, A: AttributeExt + 'a>(
                 // The following attributes are for the 3rd party crate authors.
                 // See book/src/attribs.md
                 | sym::has_significant_drop
+                | sym::no_dead_code_warning
                 | sym::format_args => None,
                 _ => {
                     sess.dcx().span_err(path_span, "usage of unknown attribute");
@@ -91,6 +93,16 @@ 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_clippy_no_dead_code_warning_attr<'a>(sess: &'a Session, tcx: TyCtxt<'_>, res: &Res) -> bool {
+    res.opt_def_id().map(|def_id| get_builtin_attr(
+        sess,
+        #[allow(deprecated)]
+        tcx.get_all_attrs(def_id),
+        sym::no_dead_code_warning,
+    ).next().is_some()).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()

src/tools/clippy/clippy_utils/src/sym.rs

@@ -439,6 +439,7 @@ generate! {
     next_if_eq,
     next_multiple_of,
     next_tuple,
+    no_dead_code_warning,
     nth,
     ok,
     ok_or,